A computational method to improve the water splitting performance of magnesium oxide nanostructure surfaces

Abstract

The present invention provides a calculation method for improving the water decomposition performance of the surface of a magnesium oxide nanostructure, including: constructing a pure magnesium oxide solid surface model and a composite material surface model; performing density functional theory calculations to determine the interface structure of the stable point; constructing a solid water molecule adsorption / decomposition configuration; constructing a composite material water molecule adsorption / decomposition configuration, and performing respective relaxations to calculate the adsorption energy and decomposition adsorption energy; calculating the charge layout, charge transfer, plane average potential and reaction potential energy curve during the adsorption and cracking process, and calculating the kinetic feasibility; determining the reaction path and reaction activation energy barrier. The present invention successfully constructs the water molecule cracking structure on the surface of the magnesium oxide nanostructure, and through quantum chemical calculation software simulation, determines the calculation reaction path and reaction activation energy barrier for improving the water decomposition performance of the magnesium oxide nanostructure surface, and it can be found that the constructed model has good adsorption and cracking capabilities for water molecules.

Description

Technical Field

[0001] The invention relates to the technical field of computational chemistry, and more particularly to a computational method for improving the water decomposition performance of the surface of a magnesium oxide nanostructure. Background Art

[0002] As a typical rock-salt ionic crystal, magnesium oxide can provide a model and reference for studying the structure-activity relationship of complex oxides. The adsorption and chemical reaction on the solid-liquid interface formed by metal oxides immersed in water are of great significance for groundwater pollutant transport, electrode processes, corrosion processes and catalytic reactions.

[0003] Giordanos et al. simulated the adsorption and partial decomposition behavior of a (3×2) layer of water on the magnesium oxide (100) surface based on the ab initio method of gradient-corrected local density approximation. This is the first theoretical discovery that water molecules can decompose on the perfect magnesium oxide (100) surface (which has been confirmed experimentally).

[0004] Metal oxides such as magnesium oxide are important components of rocks, soils and airborne dust in nature. The adsorption and decomposition behavior of water molecules on the surface of magnesium oxide still requires a lot of in-depth research. In the existing calculation method, the decomposition path of magnesium oxide surface is considered to be a one-step decomposition, with a large activation energy barrier, and the water decomposition performance of magnesium oxide surface is low. Summary of the invention

[0005] In view of this, the present invention provides a calculation method for improving the water decomposition performance of the surface of a magnesium oxide nanostructure, comprising: constructing a pure magnesium oxide solid surface model and a composite material surface model; performing density functional theory calculation on the composite material surface model to determine the stable point interface structure in the composite material surface model; constructing a solid water molecule adsorption / decomposition configuration based on the pure magnesium oxide solid surface model; constructing a composite material water molecule adsorption / decomposition configuration corresponding to the solid water molecule adsorption / decomposition configuration based on the stable point interface structure of the composite material surface model, and performing structural relaxation on the composite material water molecule adsorption / decomposition configuration to calculate the adsorption energy and decomposition adsorption energy of water molecules on the surface of a MgO / Ag composite material; calculating the charge layout, charge transfer, plane average potential and reaction potential energy curve in the adsorption and cracking process according to the composite material water molecule adsorption / decomposition configuration, and calculating the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of a MgO / Ag composite material according to the reaction potential energy curve; and determining the calculation reaction path and reaction activation energy barrier for improving the water decomposition performance of the surface of a magnesium oxide nanostructure according to molecular dynamics calculation.

[0006] Preferably, constructing the pure magnesium oxide solid surface model and the composite material surface model comprises: constructing the pure magnesium oxide solid surface model and the composite material surface model using Visual Molecular Dynamics software.

[0007] Preferably, the construction of the composite surface model includes: constructing four layers of silver atoms along the magnesium oxide surface to represent the silver substrate; fixing the two silver layers at the bottom and using them to simulate the volume characteristics of the silver layer; wherein the supercell of the composite surface model is constructed. When , the same lattice parameters a = b = 11.666 Å and c = 26.000 Å are used to construct the unit cell along the [0 -1 1] and [0 1 1] unit cell basis vectors;

[0008] Preferably, the Ag-Ag bond length of the simulated solid of the composite material surface model is 2.916 Å.

[0009] Preferably, performing density functional theory calculation on the composite material surface model to determine the stable point interface structure in the composite material surface model comprises:

[0010] For the composite material surface model, the structural energy and electronic properties are calculated using van der Waals density functional theory and a plane wave method implemented in a Vienna ab initio simulation software package to determine the stable point interface structure;

[0011] Preferably, the determining of the stable point interface structure further comprises: converting the double real space integral for dispersion correction into reciprocal space; and determining the dispersion force and energy by combining the generalized gradient approximation with the projected enhanced wave method.

[0012] Preferably, after determining the stable point interface structure in the surface model of the composite material, the method further includes: first performing a static calculation using a Vienna ab initio simulation software package to obtain a wave function output file and a CHG file; and performing a density of state calculation on the wave function output file and the CHG file to obtain a density of state calculation result; and analyzing the density of state calculation result using P4VASP software.

[0013] Preferably, constructing the solid water molecule adsorption / decomposition configuration based on the pure magnesium oxide solid surface model includes: calculating the adsorption energy and decomposition adsorption energy of water molecules on pure magnesium oxide based on the pure magnesium oxide solid surface model, obtaining adsorption and decomposition reaction sites, and constructing the solid water molecule adsorption / decomposition configuration; calculating the decomposition reaction activation energy barrier and reaction path using the VTST program based on the solid water molecule adsorption / decomposition configuration, and judging the reaction activity of the magnesium oxide solid surface.

[0014] Preferably, the stable point interface structure based on the composite material surface model constructs a composite material water molecule adsorption / decomposition configuration corresponding to the solid water molecule adsorption / decomposition configuration, and performs structural relaxation on the composite material water molecule adsorption / decomposition configuration to calculate the adsorption energy and decomposition adsorption energy of water molecules on the surface of the MgO / Ag composite material, including:

[0015] The solid water molecule adsorption / decomposition configuration is transferred to the surface of the MgO / Ag composite material to construct the composite material water molecule adsorption / decomposition configuration; a typical model is obtained, and the structure of the typical model is relaxed using the Vienna Ab Initio Simulation Package program to obtain the lowest energy model of the composite material water molecule adsorption / decomposition configuration; wherein the typical model includes the solid water molecule adsorption / decomposition configuration; based on the structure and energy of the composite material water molecule adsorption / decomposition configuration, the adsorption energy and the decomposition adsorption energy of water molecules on the surface of the MgO / Ag composite material are calculated to obtain the most favorable adsorption and decomposition structure; the geometric structure of the adsorbate molecules of the most favorable adsorption and decomposition structure is analyzed using VESTA software; based on the composite material water molecule adsorption / decomposition configuration, the Cartesian coordinates are obtained using the pos2xyz.pl program, and the surface wrinkle value is calculated.

[0016] Preferably, the adsorption energy is the difference between the total energy of the isolated molecule and the MgO / Ag composite surface and the energy of the chemically adsorbed molecule / surface system; preferably, the adsorption energy E ad The calculation method is:

[0017] ;in, is the energy of the isolated molecule; is the energy of the MgO / Ag composite surface; is the energy of the chemically adsorbed molecule / surface system.

[0018] Preferably, the charge layout, charge transfer, plane average potential and reaction potential energy curve in the adsorption and cracking process are calculated according to the adsorption / decomposition configuration of water molecules in the composite material, and the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of the MgO / Ag composite material is calculated according to the reaction potential energy curve, including:

[0019] Using Visual Molecular Dynamics quantum chemistry software and VTST program to analyze the differential charge density and the charge layout under the adsorption / decomposition configuration of water molecules in the composite material, and deriving the charge transfer of the charges adsorbed in the cracking process according to the differential charge density and the charge layout;

[0020] Characterizing the charge state of the MgO / Ag nanostructure in the adsorption / decomposition state of the composite material water molecule adsorption / decomposition configuration by the vtotav program, and deriving the plane average potential in the adsorption and decomposition process according to the charge state of the MgO / Ag nanostructure;

[0021] The decomposition path and transition state of water molecules on MgO / Ag were simulated by VTST program calculation, the reaction potential energy curve was determined, and the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of MgO / Ag composite material was obtained based on the reaction potential energy curve.

[0022] The invention provides a calculation method for improving the water decomposition performance of the surface of a magnesium oxide nanostructure, comprising: constructing a pure magnesium oxide solid surface model and a composite material surface model; performing density functional theory calculation on the composite material surface model to determine the stable point interface structure in the composite material surface model; constructing a solid water molecule adsorption / decomposition configuration based on the pure magnesium oxide solid surface model; constructing a composite material water molecule adsorption / decomposition configuration corresponding to the solid water molecule adsorption / decomposition configuration based on the stable point interface structure of the composite material surface model, performing structural relaxation on the composite material water molecule adsorption / decomposition configuration, and calculating the adsorption energy and decomposition adsorption energy of water molecules on the surface of a MgO / Ag composite material; calculating the charge layout, charge transfer, plane average potential and reaction potential energy curve in the adsorption and cracking process according to the composite material water molecule adsorption / decomposition configuration, and calculating the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of the MgO / Ag composite material according to the reaction potential energy curve; and determining the calculation reaction path and reaction activation energy barrier for improving the water decomposition performance of the magnesium oxide nanostructure surface according to molecular dynamics calculation. The present invention uses numerical calculation software Vienna Ab Initio Simulation Package and the like to perform theoretical calculations on the catalytic properties of the constructed model, thereby providing a new calculation method for improving the water decomposition performance on the surface of magnesium oxide nanostructures, and also providing a new method for the cracking mechanism of water molecules on the surface of oxide insulating materials, thereby improving the theoretical model in the existing method and laying a theoretical foundation for related experimental exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1a A schematic flow chart of a first embodiment of a calculation method for improving the water decomposition performance of a magnesium oxide nanostructure surface according to the present invention;

[0024] Figure 1b This is a schematic diagram of the overall process framework of the first embodiment of the calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures of the present invention;

[0025] Figure 2A schematic flow chart of a second embodiment of a calculation method for improving the surface water decomposition performance of magnesium oxide nanostructures according to the present invention;

[0026] Figure 3a A schematic flow chart of a third embodiment of a calculation method for improving the surface water decomposition performance of magnesium oxide nanostructures according to the present invention;

[0027] Figure 3b This is a schematic flow chart of the refinement of step S210 in the third embodiment of the calculation method for improving the water decomposition performance of the surface of the magnesium oxide nanostructure of the present invention;

[0028] Figure 3c A schematic flow chart of the steps after step S600 in the third embodiment of the calculation method for improving the water decomposition performance of the surface of the magnesium oxide nanostructure of the present invention;

[0029] Figure 4a This is a schematic flow chart of the refinement of step S300 in the fourth embodiment of the calculation method for improving the water decomposition performance of the surface of the magnesium oxide nanostructure of the present invention;

[0030] Figure 4b The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures in the fourth embodiment of the present invention is a diagram of the adsorption and dissociation structures of water on bulk magnesium oxide (001) (wherein 4b-a is the adsorption structure of water on bulk magnesium oxide (001), and 4b-b and 4b-c are the dissociation structures of water on bulk magnesium oxide (001));

[0031] Figure 4c This is a schematic flow chart of the refinement of step S400 in the fourth embodiment of the calculation method for improving the water decomposition performance of the surface of the magnesium oxide nanostructure of the present invention;

[0032] Figure 4d A schematic diagram of the equilibrium geometric configuration of water adsorption and dissociation on a magnesium oxide film in the fourth embodiment of the calculation method for improving the water decomposition performance of the magnesium oxide nanostructure surface of the present invention;

[0033] Figure 4e This is a schematic flow chart of the refinement of step S500 in the fourth embodiment of the calculation method for improving the water decomposition performance of the surface of the magnesium oxide nanostructure of the present invention;

[0034] Figure 4f The calculation method for improving the water decomposition performance of the surface of the magnesium oxide nanostructure of the present invention is a differential charge density diagram of water adsorbed on the magnesium oxide film in the fourth embodiment (wherein the differential charge density isosurface value is 0.002e bohr -3 );

[0035] Figure 4gThe calculation method for improving the water decomposition performance of the surface of the magnesium oxide nanostructure of the present invention is the plane average potential diagram of water adsorption (A state) and dissociation (D4 state) along the y and z directions (perpendicular to the magnesium oxide layer) on the magnesium oxide-silver composite material in the fourth embodiment;

[0036] Figure 4h The unstable dissociative adsorption structure diagram of water on the silver-loaded magnesium oxide film in the fourth embodiment of the calculation method for improving the water decomposition performance of the magnesium oxide nanostructure surface of the present invention;

[0037] Figure 4i In the fourth embodiment of the calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures of the present invention, the CI-NEB method is used to obtain the water decomposition path image of the composite material and the structural schematic diagrams of the initial state (IS), transition state (TS), intermediate state (IM) and final state (FS).

[0038] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Unless otherwise defined hereinafter, the meaning of all technical terms and scientific terms used in the specific embodiments of the present invention are intended to be the same as those generally understood by those skilled in the art. Although it is believed that the following terms are well understood by those skilled in the art, the following definitions are still set forth to better explain the present invention.

[0041] As used in the present invention, the terms "comprise", "comprising", "having", "containing" or "involving" are inclusive or open-ended, and do not exclude other unrecited elements or method steps. The term "consisting of" is considered to be a preferred embodiment of the term "comprising". If a group is defined below as comprising at least a certain number of embodiments, this should also be understood to disclose a group that preferably consists of only these embodiments.

[0042] When referring to a singular noun an indefinite or definite article e.g. "a" or "an", "the" is used, this includes a plural of that noun.

[0043] The term "approximately" in the present invention indicates an accuracy range that can be understood by those skilled in the art and still ensures the technical effect of the characteristic in question. The term generally indicates ±10%, preferably ±5%, of the indicated value.

[0044] In addition, the terms first, second, third, (a), (b), (c), and the like in the specification and claims are used to distinguish similar elements and are not necessarily required to describe a sequential or chronological order. It should be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments described in the present invention can be implemented in other sequences than those described or illustrated in the present invention.

[0045] The following is provided merely to aid understanding of the present invention. These definitions should not be construed to have a scope less than that understood by those skilled in the art.

[0046] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but does not constitute any limitation to the present invention. Any limited modifications made by anyone within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0047] Embodiment 1:

[0048] Reference Figure 1a ,as well as Figure 1b The first embodiment of the present invention provides a calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures, comprising:

[0049] Step S100, constructing a pure magnesium oxide solid surface model and a composite material surface model.

[0050] In this embodiment, quantum chemical simulation software is used to build surface supercell models of different magnesium oxide crystal faces and silver surfaces, including pure magnesium oxide solid surface models and composite material surface models. The vacuum layer thickness is greater than 17 Å. MgO / Ag single crystal surface models of different size thickness configurations are obtained.

[0051] Step S200, performing density functional theory calculation on the surface model of the composite material to determine the stable point interface structure in the surface model of the composite material;

[0052] It should be noted that density functional theory (DFT) is a method for studying the electronic structure of multi-electron systems. Density functional theory has a wide range of applications in physics and chemistry, especially for studying the properties of molecules and condensed matter. It is one of the most commonly used methods in the fields of condensed matter physics, computational materials science, and computational chemistry. The most common application of density functional theory is achieved through the Kohn-Sham method. In the framework of Kohn-Sham DFT, the most difficult multi-body problem (caused by the interaction of electrons in an external electrostatic potential) is simplified to a problem of non-interacting electrons moving in an effective potential field.

[0053] The density functional theory calculations mentioned above were performed using van der Waals density functional theory (optB88-vdw).

[0054] As mentioned above, the surface model of the composite material is calculated based on the density functional theory using the quantum chemical method, thereby obtaining the most stable structural model, that is, the stable point structure with the lowest energy, which is the stable point interface structure in the surface model of the composite material.

[0055] Step S300, constructing a solid water molecule adsorption / decomposition configuration based on the pure magnesium oxide solid surface model.

[0056] Step S400, based on the stable point interface structure of the composite material surface model, constructing a composite material water molecule adsorption / decomposition configuration corresponding to the solid water molecule adsorption / decomposition configuration, and performing structural relaxation on the composite material water molecule adsorption / decomposition configuration to calculate the adsorption energy and decomposition adsorption energy of water molecules on the surface of the MgO / Ag composite material;

[0057] As mentioned above, the water molecule adsorption / decomposition configuration of the composite material corresponding to the solid water molecule adsorption / decomposition configuration is a configuration similar to the solid water molecule adsorption / decomposition configuration.

[0058] In the above, the quantum chemical method is used to perform structural relaxation on the adsorption / decomposition configuration of water molecules in the composite material based on density functional theory.

[0059] Among them, the water molecule adsorption / decomposition configuration of the composite material includes the water molecule adsorption configuration of the composite material and the water molecule decomposition configuration of the composite material.

[0060] It should be noted that structure relaxation refers to the phenomenon that the atomic arrangement inside metallic glass (amorphous metal) changes slowly over time or under annealing conditions, gradually changing into a more stable atomic arrangement structure.

[0061] As described above, based on the solid water molecule adsorption / decomposition configuration, a composite material water molecule adsorption / decomposition configuration similar thereto is constructed, and the composite material water molecule adsorption / decomposition configuration corresponds to the solid water molecule adsorption / decomposition configuration.

[0062] Step S500, calculating the charge layout, charge transfer, plane average potential and reaction potential energy curve in the adsorption and cracking process according to the adsorption / decomposition configuration of water molecules in the composite material, and calculating the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of the MgO / Ag composite material according to the reaction potential energy curve;

[0063] As mentioned above, charge distribution refers to the charge density distribution of the charged body. Charge transfer refers to the charge transfer situation, which is the situation and state of charge transfer occurring during the adsorption and decomposition reaction process.

[0064] As mentioned above, the potential energy curve, also known as the potential energy diagram, provides a visual means of studying the movement of objects in a potential field. The advantage of the potential energy diagram over the thermochemical equation is that the potential energy diagram can represent the transition state energy, which is the basis for the study of dynamics. There are two types of potential energy diagrams. One is a potential energy diagram that takes a single molecule as the research object and represents the energy difference caused by different conformations. The other is a reaction potential energy diagram that takes the reaction system as the research object and represents the energy difference of each system during the reaction.

[0065] The reaction potential energy diagram includes the following parts: coordinate axis, reactant system and product system, transition state, intermediate, potential energy curve. The two aspects that need attention are the potential energy difference between reactants and products (reaction enthalpy change) and the potential energy difference between reactants and intermediates.

[0066] It should be noted that the reaction enthalpy change: the reaction enthalpy change is the key to determining the reaction equilibrium constant. The low yield of an organic reaction is usually the result of a small reaction enthalpy change (another possibility is that the reaction is too slow, but in this case a catalyst is usually chosen).

[0067] Potential energy difference between intermediates: It can reflect the total energy change of the system during the reaction, and is also a data indicator to measure whether the mechanism is reasonable.

[0068] Step S600, determining the calculated reaction path and reaction activation energy barrier for improving the water decomposition performance of the surface of the magnesium oxide nanostructure according to molecular dynamics calculation.

[0069] As mentioned above, molecular dynamics is a comprehensive technology that combines physics, mathematics and chemistry. Molecular dynamics is a set of molecular simulation methods that mainly rely on Newtonian mechanics to simulate the movement of molecular systems, extract samples from systems composed of different states of molecular systems, and calculate the configuration integral of the system. Based on the results of the configuration integral, the thermodynamic quantities and other macroscopic properties of the system are further calculated.

[0070] This embodiment provides a new calculation method for improving the water decomposition performance on the surface of magnesium oxide nanostructures, and also provides a new method for the cracking mechanism of water molecules on the surface of oxide insulating materials, improves the theoretical model in the existing method, and lays a theoretical foundation for related experimental exploration.

[0071] Embodiment 2:

[0072] refer to Figure 2 Based on Example 1, Example 2 of the present invention provides a calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures, wherein the step S100, constructing a pure magnesium oxide solid surface model and a composite material surface model, comprises:

[0073] Step S110, using Visual Molecular Dynamics software to construct the pure magnesium oxide solid surface model and the composite material surface model.

[0074] As mentioned above, Visual Molecular Dynamics software is a chemical drawing and molecular motion analysis tool. It can provide researchers with visual motion simulations of biochemical molecules.

[0075] The above method may further include, before step S110:

[0076] Search the inorganic crystal database to find the lattice constants and fractional coordinates of magnesium oxide and metallic silver.

[0077] Afterwards, step S110 is performed according to the lattice constant and fractional coordinates of metallic silver, and the pure magnesium oxide solid surface model and the composite material surface model are constructed using Visual Molecular Dynamics software.

[0078] Furthermore, in step S110, the construction of the composite material surface model includes:

[0079] Four layers of silver atoms were constructed along the magnesium oxide surface to represent the silver substrate.

[0080] After the two bottom silver layers are fixed, they are used to simulate the structural features of solid silver.

[0081] As mentioned above, after obtaining the lattice constants and fractional coordinates of magnesium oxide and metallic silver, the Visual Molecular Dynamics software was used to construct the solid surface model of pure magnesium oxide and the surface model of the composite material. Specifically, four layers of silver atoms were constructed along the magnesium oxide (001) surface to represent the silver substrate. After fixing the two silver layers at the bottom, they were used to simulate the structural characteristics of solid silver.

[0082] Among them, the supercell of the composite material surface model is constructed The same lattice parameters a=b=11.666 Å and c =26.000 Å were used to construct the unit cell along the [0 -1 1] and [0 1 1] unit cell basis vectors.

[0083] Furthermore, the Ag-Ag bond length of the simulated solid of the composite material surface model is 2.916 Å.

[0084] In this embodiment, Visual Molecular Dynamics software is used to construct the pure magnesium oxide solid surface model and the composite material surface model, wherein the magnesium oxide solid surface model and the composite material model are the basis for the water molecule reaction in the present invention, providing a basis for obtaining further experimental data.

[0085] Embodiment 3:

[0086] Reference Figure 3a Based on Example 2, the third embodiment of the present invention provides a calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures. In which, the step S200 performs density functional theory calculation on the surface model of the composite material to determine the stable point interface structure in the surface model of the composite material, including:

[0087] Step S210, for the composite surface model, the plane wave method implemented in the van der Waals density functional theory and the Vienna ab initio simulation software package is used to calculate the structural energy and electronic properties, and determine the interface structure of the stable point. This method retains the computational efficiency of the pseudo-potential method and approaches the computational accuracy of the full-potential method, making the Vienna ab initio calculation software have a strong computational efficiency and accelerating the convergence speed of electronic self-consistency and molecular dynamics calculations.

[0088] For further reference, Figure 3b , in the step S210, determining the stable point interface structure further comprises: step S211, converting the double real space integral for dispersion correction into reciprocal space;

[0089] Step S212, using the generalized gradient approximation combined with the projected enhanced wave method to determine the dispersion force and energy.

[0090] As mentioned above, the double real space integral for dispersion correction is converted to reciprocal space to reduce the computational workload. The generalized gradient approximation (GGA) is combined with the projected augmented wave (PAW) method to determine the dispersion force and energy.

[0091] For further reference, Figure 3c After determining the stable point interface structure in the composite material surface model in step S200, the method further includes:

[0092] Step S700, using the Vienna ab initio simulation software package to perform static calculations first, and obtain a wave function output file and a CHG file;

[0093] Step S800, performing state density calculation on the wave function output file and the CHG file to obtain a state density calculation result;

[0094] Step S900, using P4VASP software to analyze the state density calculation results, it can be concluded that the oxygen atoms on the surface of the MgO / Ag composite material are at a higher energy level, reflecting that the metal-loaded oxide film should have a higher catalytic reaction activity.

[0095] As mentioned above, after determining the stable point interface structure in the composite material surface model, the catalytic activity prediction of the MgO / Ag model is performed. The electronic structure of the surface atoms of the MgO / Ag stable point interface structure has an important influence on its reaction activity.

[0096] Among them, the Vienna ab initio simulation software package was used to perform static calculations first, and wave function output files and CHG files were obtained. Among them, the distance between the 2p energy level of oxygen atoms on the MgO / Ag surface and the Fermi level was calculated to measure the catalyst activity. In order to accurately calculate the exchange-correlation potential, the correlation part of the optB88 vdW functional was optimized to take into account the dispersion interaction.

[0097] This nonlocal functional belongs to the van der Waals density functional, first proposed by Dean and his colleagues. The exchange-correlation potential of the van der Waals density functional is calculated by the following expression:

[0098] ;

[0099] where GGA exchange energy, LDA correlation energy and nonlocal correlation energy are expressed as , and .

[0100] In addition, in order to further overcome the shortcomings of the PBE type functional, the B88 exchange enhancement factor was used to correct the GGA exchange energy density. The following formula is used:

[0101] ; where c, β, μ are optimization constants, and s represents the simplified density gradient. For the plane wave basis set, the kinetic energy cutoff is 500 eV. The 2×2×1 and 4×4×1 k-point grids at the gamma center are used to sample the Brillouin zone for structural relaxation and static properties, respectively.

[0102] In this embodiment, after determining the stable point interface structure in the surface model of the composite material, the catalytic activity of the MgO / Ag model is predicted, and the catalyst activity is measured by calculating the distance between the 2p energy level of oxygen atoms on the MgO / Ag surface and the Fermi level based on the optB88 vdW functional theory. Based on the prediction of the 2p energy level of O atoms, it can be concluded that the metal-loaded oxide film MgO / Ag has higher catalytic activity than solid magnesium oxide.

[0103] Embodiment 4:

[0104] Reference Figure 4a Based on Example 1, the fourth embodiment of the present invention provides a calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures. In which, the step S300, based on the pure magnesium oxide solid surface model, constructs a solid water molecule adsorption / decomposition configuration, including:

[0105] Step S310, based on the pure magnesium oxide solid surface model, calculating the adsorption energy and desorption energy of water molecules on pure magnesium oxide, obtaining adsorption and decomposition reaction sites, and constructing the solid water molecule adsorption / decomposition configuration;

[0106] At the optB88-vdw theoretical level of van der Waals density functional theory, the adsorption energy of water after adsorption by pristine magnesium is -0.641 eV. Since there are two possible structures after dissociation, the two dissociation adsorption energies are 0.451 eV respectively (reference Figure 4b b) and 0.478 eV (reference Figure 4b (c) The two dissociation adsorption energies are similar and both are positive, which indicates that the dissociation of water on pure magnesium oxide is unfavorable in terms of energy. For water molecules on the surface of pure magnesium oxide (001), the wrinkle values ​​of the first oxide layer to the fourth oxide layer in the dissociated state are 0.564, 0.170, 0.043 and 0.016 Å, respectively, which greatly distorts the structure of the oxide material.

[0107] Step S320, based on the adsorption / decomposition configuration of the solid water molecules, the activation energy barrier and reaction path of the decomposition reaction are calculated using the VTST program to determine the reaction activity of the magnesium oxide solid surface.

[0108] The calculated distances between the Ow-H bonds in the molecular adsorption state are 1.015 and 0.974 Å, respectively, indicating that the OH bonds near the magnesium oxide surface are slightly activated. The CI-NEB technology was used to predict the reaction path, and the results showed that the decomposition of water on the magnesium oxide solid surface requires a large activation barrier of 1.113 eV, so the dissociation process on the magnesium oxide solid surface has no advantage, proving that its kinetics are not feasible.

[0109] For further reference, Figure 4cThe step S400, based on the stable point interface structure of the composite material surface model, constructs a composite material water molecule adsorption / decomposition configuration corresponding to the solid water molecule adsorption / decomposition configuration, and performs structural relaxation on the composite material water molecule adsorption / decomposition configuration to calculate the adsorption energy and decomposition adsorption energy of water molecules on the surface of the MgO / Ag composite material, including:

[0110] Step S410, transferring the solid water molecule adsorption / decomposition configuration to the surface of the MgO / Ag composite material to construct a composite water molecule adsorption / decomposition configuration; obtaining a typical model, and performing structural relaxation on the typical model using the Vienna Ab Initio Simulation Package program to obtain a minimum energy model of the composite water molecule adsorption / decomposition configuration; wherein the typical model includes the solid water molecule adsorption / decomposition configuration;

[0111] In the above, on the composite material water molecule adsorption / decomposition configuration of the composite material surface model (MgO / Ag model) with better stability obtained in the previous steps, the solid water molecule adsorption / decomposition configuration was copied or referred to, and water molecules were added 2.15 angstroms above different surface sites of the MgO / Ag composite material using Visual Molecular Dynamics quantum chemistry software to construct the adsorption state structure model of water molecules adsorbed on different active sites. The Vienna Ab InitioSimulation Package program was used to perform structural relaxation on the typical model to obtain various water molecule adsorption and decomposition stable point structures and energies.

[0112] Step S420, based on the structure and energy of the adsorption / decomposition configuration of water molecules in the composite material, calculating the adsorption energy and decomposition adsorption energy of water molecules on the surface of the MgO / Ag composite material, so as to obtain the most favorable adsorption and decomposition structure;

[0113] As mentioned above, the isolated molecule (E iso ) and bare MgO surface (or MgO / Ag composite surface, denoted as E surf ) and the total energy of the chemically adsorbed molecule / surface system (E chemisorb ) The difference between the two energies is defined as the adsorption energy (E ad ), as shown below:

[0114] ;

[0115] At the optB88-VDW level of theory, the D1 state has a higher energy (0.171 eV) than the A state, and the dissociative adsorption energy is -0.466 eV. Although the hydroxyl group binds to two surface magnesiums, the adsorption energy of the D2 state is slightly smaller than that of the D1 state.w H) can also be derived from surface hydroxyl groups (O s H) moves away to form D3 state, and the dissociation adsorption energy is -0.313 eV. The hydroxyl group of the dissociated state D4 has the opposite hydrogen bond direction to that of the D3 state, showing a strong H1-O w Hydrogen bond, slightly lower energy than D3 state (E ad = -0.329 eV), D4 is thermodynamically most favorable for the adsorption and decomposition of water molecules.

[0116] The positive dissociation adsorption energy of the D5 state is 0.971 eV. Figure 4h describes the oxygen adsorbed atoms and surface hydroxyl groups (O s H) More unstable dissociative adsorption structures. The dissociative adsorption energies of the D6, D7, and D8 states are 2.289 eV, 2.435 eV, and 2.325 eV, respectively.

[0117] Step S430, using VESTA software to perform geometric structure analysis of the adsorbate molecules on the most favorable adsorption and decomposition structure;

[0118] For the adsorption and dissociation of water molecules on magnesium oxide films, at the optB88-vdw theoretical level, the molecular adsorption state (ref. Figure 4d A) shows that H w Adsorbed on O s -Mg s The distance between H-O bonds is 1.013 and 0.974 Å, respectively, which is similar to the distance between H-O bonds in solid MgO. w The distance between the H-Os bonds is very close. The calculated distance between H-Os is 1.753 Å. When the molecular adsorption state (A) is changed to the decomposition state D1, O w -Mg bond is strengthened, O w The distance between D2 and Mg is shortened from 2.170 Å to 1.974 Å. 2 - The Ow distance is shortened to 2.167 Å, ​​which means μ 2 - Formation of OH.

[0119] Step S440, based on the water molecule adsorption / decomposition configuration of the composite material, a coordinate conversion program pos2xyz.pl is used to obtain Cartesian coordinates and calculate the surface wrinkle value.

[0120] At the optB88 - vdW level of theory, the wrinkle values ​​of the A, D1 and D2 states were calculated to be 0.356 Å, 0.551 Å and 0.651 Å, respectively. In the dissociated states D3 and D4, the surface distortion is large, indicating that the wrinkle value is close to 0.9 Å.

[0121] Further, the adsorption energy is the difference between the total energy of the isolated molecule and the MgO / Ag composite surface and the energy of the chemically adsorbed molecule / surface system;

[0122] Furthermore, the adsorption energy E ad The calculation method is:

[0123] ;

[0124] in, is the energy of the isolated molecule; is the energy of the MgO / Ag composite surface; is the energy of the chemically adsorbed molecule / surface system.

[0125] For further reference, Figure 4e The step S500, according to the adsorption / decomposition configuration of water molecules in the composite material, calculates the charge layout, charge transfer, plane average potential and reaction potential energy curve in the adsorption and cracking process, and calculates the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of the MgO / Ag composite material according to the reaction potential energy curve, including:

[0126] Step S510, using Visual Molecular Dynamics quantum chemistry software and VTST program to analyze the differential charge density and the charge layout under the water molecule adsorption / decomposition configuration of the composite material, and deriving the charge transfer of the charges adsorbed in the cracking process according to the differential charge density and the charge layout;

[0127] The Visual Molecular Dynamics package and VTST program were used to analyze the Differential Charge Density and Bader charge layout under the optimized configuration, and the charge transfer during adsorption and cleavage was analyzed. Figure 4f .

[0128] Step S520, characterizing the charge state of the MgO / Ag nanostructure in the adsorption / decomposition state under the water molecule adsorption / decomposition configuration of the composite material through the vtotav program, and deriving the plane average potential during the adsorption and decomposition process according to the charge state of the MgO / Ag nanostructure.

[0129] The charge state of the MgO / Ag nanostructure in the adsorption and decomposition state was characterized by the vtotav program to determine whether the surface charge distribution state was greatly distorted before and after adsorption and decomposition. Combined with the size of the structural distortion and charge distortion, it was comprehensively judged that the catalyst had high stability. Figure 4gis the planar average potential of water adsorption (A state) and dissociation (D4 state) on the MgO-Ag composite along the y and z directions (perpendicular to the MgO layer).

[0130] Step S530, calculating and simulating the decomposition path and transition state of water molecules on MgO / Ag through the VTST program, determining the reaction potential energy curve, and obtaining the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of the MgO / Ag composite material based on the reaction potential energy curve.

[0131] The VTST program is used to simulate the decomposition path and transition state of water molecules on MgO / Ag, determine the reaction potential energy curve, and judge the kinetic feasibility of the catalyst model. For the pure magnesium oxide solid surface, this process is an endothermic elementary reaction with no intermediate state.

[0132] Furthermore, the reaction potential energy curve shows that the dissociation state of water molecules on the surface of MgO / Ag composite materials should go through an intermediate state (O w -H distance 1.403 Å), such as Figure 4i .

[0133] This reaction pathway involving the intermediate state improves the dissociation channel previously reported in several academic journals ([1]Jung J, Shin HJ, Kim Y, et al. Controlling water dissociation on anultrathin MgO film by tuning film thickness[J]. Physical Review B, 2010, 82(8): 085413.[2] Song Z, Zhao B, Wang Q, et al. Homolytic cleavage of water onmagnesia film promoted by interfacial oxide− metal nanocomposite[J]. AppliedSurface Science, 2019, 487: 1222-1232.[3] Shin HJ, Jung J, Motobayashi K, etal. State-selective dissociation of a single water molecule on an ultrathinMgO film[J]. Nature materials, 2010, 9(5): 442-447.), and can greatly reduce the reaction activation barrier for the dissociation of water molecules. Based on dispersion-corrected density functional theory calculations, a fully dissociated state (D4) can be obtained by crossing two small activation barriers (0.173 eV and 0.355 eV).

[0134] In summary, the present invention provides a new calculation method for improving the water decomposition performance on the surface of magnesium oxide nanostructures through theoretical calculation of the catalytic properties of the constructed model using numerical calculation software such as Vienna Ab Initio Simulation Package, and also provides a new method for the cracking mechanism of water molecules on the surface of oxide insulating materials, thereby improving the theoretical model in the existing method and laying a theoretical foundation for related experimental exploration.

[0135] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0136] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product is stored in a storage medium (such as ROM / RAM, disk, CD) as described above, including a number of instructions for a terminal device (which can be a mobile phone, computer, server, or network device, etc.) to execute the methods described in each embodiment of the present invention. The above is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly used in other related technical fields, are similarly included in the patent protection scope of the present invention.

Claims

1. A calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures, characterized in that: include: Construct pure magnesium oxide solid surface model and composite material surface model; Performing density functional theory calculation on the surface model of the composite material to determine the stable point interface structure in the surface model of the composite material; Based on the pure magnesium oxide solid surface model, the adsorption energy and decomposition energy of water molecules on pure magnesium oxide are calculated to obtain adsorption and decomposition reaction sites, and the adsorption / decomposition configuration of solid water molecules is constructed; Based on the adsorption / decomposition configuration of the solid water molecules, the activation energy barrier and reaction path of the decomposition reaction are calculated using the VTST program to determine the reaction activity of the magnesium oxide solid surface; Transferring the solid water molecule adsorption / decomposition configuration to the surface of the MgO / Ag composite material to construct a composite water molecule adsorption / decomposition configuration; obtaining a typical model, and performing structural relaxation on the typical model using the Vienna Ab Initio Simulation Package program to obtain a minimum energy model of the composite water molecule adsorption / decomposition configuration; wherein the typical model includes the solid water molecule adsorption / decomposition configuration; Based on the structure and energy of the adsorption / decomposition configuration of water molecules in the composite material, the adsorption energy and the decomposition adsorption energy of water molecules on the surface of the MgO / Ag composite material are calculated to obtain the most favorable adsorption and decomposition structure; Using VESTA software to analyze the geometric structure of the adsorbate molecules for the most favorable adsorption and decomposition structure; Based on the water molecule adsorption / decomposition configuration of the composite material, the Cartesian coordinates are obtained using the pos2xyz.pl program, and the surface wrinkle values ​​are calculated; According to the adsorption / decomposition configuration of water molecules in the composite material, the charge layout, charge transfer, plane average potential and reaction potential energy curve in the adsorption and cracking process are calculated, and the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of the MgO / Ag composite material is calculated according to the reaction potential energy curve; Based on molecular dynamics calculations, the calculated reaction pathways and reaction activation energy barriers for improving the water splitting performance on the surface of magnesium oxide nanostructures were determined.

2. The method for calculating the water decomposition performance of the surface of magnesium oxide nanostructures according to claim 1, characterized in that: The method of constructing a pure magnesium oxide solid surface model and a composite material surface model comprises: The pure magnesium oxide solid surface model and the composite material surface model were constructed using Visual Molecular Dynamics software.

3. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures as claimed in claim 2, characterized in that: The construction of the composite material surface model includes: Four layers of silver atoms were constructed along the magnesium oxide surface to represent the silver substrate; After fixing the two bottom silver layers, use it to simulate the volume characteristics of the silver layer; Among them, the supercell of the composite material surface model is constructed The same lattice parameters a=b=11.666 Å and c =26.000 Å were used to construct the unit cell along the [0 -1 1] and [0 1 1] unit cell basis vectors.

4. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures as claimed in claim 3, characterized in that: The Ag-Ag bond length of the simulated solid of the composite surface model is 2.916 Å.

5. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures as claimed in claim 1, characterized in that: The performing density functional theory calculation on the composite material surface model to determine the stable point interface structure in the composite material surface model comprises: For the composite material surface model, the structural energy and electronic properties are calculated using van der Waals density functional theory and a plane wave method implemented in a Vienna ab initio simulation software package to determine the stable point interface structure.

6. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures as claimed in claim 5, characterized in that: Determining the stable point interface structure further comprises: Convert the double real-space integral used for dispersion correction to reciprocal space; The generalized gradient approximation is combined with the projected augmented wave method to determine the dispersion forces and energies.

7. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures as claimed in claim 1, characterized in that: After determining the stable point interface structure in the composite material surface model, the method further includes: Use the Vienna ab initio simulation software package to first perform static calculations and obtain wave function output files and CHG files; and performing state density calculation on the wave function output file and the CHG file to obtain a state density calculation result; The P4VASP software was used to analyze the state density calculation results.

8. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures as claimed in claim 1, characterized in that: The adsorption energy is the difference between the total energy of the isolated molecule and the MgO / Ag composite surface and the energy of the chemically adsorbed molecule / surface system.

9. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructures as claimed in claim 8, characterized in that: The adsorption energy E ad The calculation method is: ； in, is the energy of the isolated molecule; is the energy of the MgO / Ag composite surface; is the energy of the chemically adsorbed molecule / surface system.

10. The calculation method for improving the water decomposition performance of the surface of magnesium oxide nanostructure according to claim 1, characterized in that: The charge layout, charge transfer, plane average potential and reaction potential energy curve in the adsorption and cracking process are calculated based on the adsorption / decomposition configuration of water molecules in the composite material, and the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of the MgO / Ag composite material is calculated based on the reaction potential energy curve, including: Using Visual Molecular Dynamics quantum chemistry software and VTST program to analyze the differential charge density and the charge layout under the adsorption / decomposition configuration of water molecules in the composite material, and deriving the charge transfer of the charges adsorbed in the cracking process according to the differential charge density and the charge layout; Characterizing the charge state of the MgO / Ag nanostructure in the adsorption / decomposition state of the composite material water molecule adsorption / decomposition configuration by the vtotav program, and deriving the plane average potential in the adsorption and decomposition process according to the charge state of the MgO / Ag nanostructure; The decomposition path and transition state of water molecules on MgO / Ag were simulated by VTST program calculation, the reaction potential energy curve was determined, and the kinetic feasibility of the adsorption and decomposition reaction of water molecules on the surface of MgO / Ag composite material was obtained based on the reaction potential energy curve.

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