A calculation method for the adsorption performance of water molecules on the surface of rare earth element-doped iron

Abstract

The present invention discloses a method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron. The method comprises: firstly, constructing a reasonable surface model through software modeling, doping rare earth elements into the surface model, then adsorbing water molecules on the doped surface model, calculating the adsorption energy through first principle calculation, determining the optimal adsorption site of water molecules, and then using molecular dynamics to calculate the changes in the adsorption energy and adsorption site of water molecules with increasing temperature. Finally, electronic performance calculations are used to analyze the transfer of electrons and changes in surface bonding after the adsorption of water molecules. The present invention studies the adsorption of water molecules on the surface of rare earth element-doped iron from a computational perspective, provides a data basis for studying the influence of water molecules adsorbed on metal surfaces on metal properties, and further fundamentally explains the mechanism of corrosion, laying the foundation for solving the corrosion problem of steel materials.

Description

Technical Field

[0001] The present invention relates to the technical field of calculation of the adsorption performance of water molecules on metal surfaces, and in particular to a method for calculating the adsorption performance of water molecules on a rare earth element-doped iron surface. Background Art

[0002] The adsorption of water molecules on metal surfaces plays a key role in studying metal catalysis and corrosion. For a long time, steel has been deeply integrated into various aspects of people's lives and is the most widely used metal material.

[0003] However, the corrosion problem of steel materials has never been well solved. To this end, researchers have conducted a lot of exploration and have improved the corrosion resistance of steel materials to a certain extent through surface coating, alloying to enhance corrosion resistance, etc., but the effect is extremely limited. Summary of the Invention

[0004] In view of this, the present invention provides a method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron. By calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron, the adsorption of water molecules on the surface of rare earth element-doped iron is studied, the corrosion mechanism is fundamentally explained, and the corrosion problem of steel materials is solved.

[0005] The present invention is implemented by the following scheme:

[0006] The present invention provides a method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron, the method comprising:

[0007] Establish the crystal unit cell structure of metallic iron, optimize the lattice parameters of the unit cell, and obtain the lattice parameters of the stable unit cell;

[0008] Based on the stable unit cell, a structural model of the surface to be calculated is established, and the surface energy is calculated using the first-principles calculation method;

[0009] Optimize the structure of water molecules, add the optimized water molecules to a certain height above the surface layer of the iron surface model, optimize the structure, find the best adsorption site, and calculate the adsorption energy;

[0010] Rare earth elements are doped into the surface model to obtain the doped iron unit cell structure. Optimized water molecules are added to a certain height above the surface of the iron unit cell structure, and the structure is optimized to find the optimal adsorption site and calculate the adsorption energy.

[0011] Based on the final adsorption model after doping and combined with molecular dynamics methods, the changes in the adsorption energy and adsorption sites of water molecules with increasing temperature are calculated;

[0012] The electron transfer and changes in surface bonding after water molecule adsorption are analyzed through electronic property calculations.

[0013] Furthermore, the surface energy is calculated as follows:

[0014] E surf =(E slab –nE bulk ) / 2A;

[0015] Among them, E surf is the surface energy, E slab is the total energy of the surface model, E bulk is the energy of a single atom of the iron unit cell, the value of n is equal to the total number of atoms in the surface model, and A is the surface area of the model surface under study.

[0016] Furthermore, the calculation formula of the adsorption energy is:

[0017] E ad =E total –E slab –E H2O ,

[0018] Among them, E ad is the adsorption energy, E total is the total energy of the adsorption system, E slab is the total energy of the surface model, E H2O is the energy of a single water molecule.

[0019] Furthermore, combined with molecular dynamics methods, the changes in the adsorption energy and adsorption sites of water molecules with increasing temperature were calculated, including: molecular dynamics calculations using Materials Studio software at temperatures of 100K, 300K, and 450K to observe the changes in the adsorption of water molecules on the surface with changes in temperature.

[0020] Furthermore, after the structural model of the surface to be calculated is established, the method further includes: adding a vacuum layer as needed.

[0021] Furthermore, before establishing the structural model of the surface to be calculated, it also includes: taking the number of atomic layers and the vacuum layer thickness as independent variables and the surface energy as the dependent variable, performing a convergence test on the vacuum layer thickness and the number of atomic layers.

[0022] Advantages and positive effects of the present invention: The present invention studies the adsorption of water molecules on the surface of rare earth element-doped iron from a computational perspective, providing a data basis for studying the influence of water molecules adsorbed on the metal surface on the metal properties, thereby fundamentally explaining the mechanism of corrosion and laying the foundation for solving the corrosion problem of steel materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] Figure 1 This is a flow chart of a method for calculating the adsorption performance of water molecules on a rare earth element-doped iron surface according to an embodiment of the present invention;

[0025] Figure 2 This is a model grain boundary energy convergence test diagram constructed based on a typical example of the present invention;

[0026] Figure 3 This is a diagram of a water molecule surface adsorption model of a typical example of the present invention;

[0027] Figure 4 This is a schematic diagram of possible adsorption sites of water molecules in a typical example of the present invention;

[0028] Figure 5 It is a differential charge density diagram of a water molecule stable adsorption system based on a typical example of the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0030] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0031] The software used in the examples include Materials Studio and VESTA.

[0032] like Figure 1 As shown, a method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron in an embodiment of the present invention is based on a first-principles calculation method to study the adsorption of water molecules on the surface of rare earth element-doped steel materials, and specifically includes the following steps:

[0033] Step 1: Establish the crystal unit cell structure of metallic iron and optimize the lattice parameters of the unit cell to obtain the lattice parameters of the stable unit cell. Based on the stable unit cell, establish the structural model of the surface to be studied and add a vacuum layer of appropriate thickness as needed.

[0034] In some embodiments, in order to obtain accurate lattice constants of metal unit cells, the iron crystal unit cell in step 1 needs to be fully relaxed and optimized. Before formal modeling, a convergence test is required. In this example, the number of atomic layers and the vacuum layer thickness are used as independent variables, and the surface energy is used as the dependent variable. Convergence tests are performed on the vacuum layer thickness and the number of atomic layers, such as Figure 2 As shown in Figure 2, the surface energy first increases and then tends to be stable with the increase of the number of atomic layers and the thickness of the vacuum layer. It should be clear that in order to establish an accurate model, the number of atomic layers and the thickness of the vacuum layer of the model must satisfy the minimum number of atomic layers and the minimum vacuum layer thickness corresponding to the stable grain boundary energy, for example Figure 2 The minimum number of atomic layers and the minimum vacuum layer thickness for a stable grain boundary are shown in Then the number of atomic layers and the thickness of the vacuum layer of the unit cell model must be greater than or equal to 7 layers and

[0035] Step 2: Analyze the pseudopotential file to obtain the plane wave cutoff energy information. Use the first-principles calculation method to perform preliminary structural optimization on the surface model constructed in step 1 to obtain a stable unit cell structure and lattice parameters, and calculate the surface energy.

[0036] In the specific implementation, the pseudopotential file is analyzed to obtain the plane wave cutoff energy information, and the surface model in step 2 is structurally optimized using Materials Studio software to obtain a stable unit cell structure and unit cell parameters. When optimizing the surface model, the position of the bottom-layer atoms must be fixed, and only the atomic position is optimized without optimizing the unit cell structure. After optimization, the surface energy of the structure is calculated.

[0037] The surface energy is calculated as follows:

[0038] E surf =(E slab –nE bulk ) / 2A, (1)

[0039] Among them, E surf is the surface energy, E slab is the total energy of the surface model, Ebulk is the energy of a single atom of the iron unit cell, the value of n is equal to the total number of atoms in the surface model, and A is the surface area of the model surface.

[0040] Step 3: Optimize the structure of water molecules, add the optimized water molecules to the appropriate position at a certain height above the surface layer of the iron surface model, and optimize the structure to find the best adsorption site and calculate the adsorption energy.

[0041] In the specific implementation, the structure of water molecules is optimized and the optimized water molecules are added to a certain height above the optimized surface model. The position of the water molecules is noted. Possible adsorption sites of water molecules include directly above the atom (top position), directly above the adjacent atomic bond (bridge position), directly above the atomic gap (interstitial position), etc. By adsorbing water molecules at these positions respectively and comparing the adsorption energy, the best adsorption site is determined. Figure 3 The following is an adsorption model diagram of a typical example. Figure 3 (a)-(b) represent the stable adsorption configurations of water molecules on the close-packed hexagonal iron (1000) surface without rare earth element doping and with rare earth element doping, respectively. Figure 4 The green circles in the middle represent possible adsorption sites. Figure 4 (a)-(c) correspond to the top position, bridge position, and gap position, respectively. The adsorption energy results of water molecules at the three positions are shown in Table 1.

[0042] The adsorption energy calculation formula is:

[0043] E ad =E total –E slab –E H2O , (2)

[0044] Among them, E ad is the adsorption energy, E total is the total energy of the adsorption system, E slab is the total energy of the surface model, E H2O It is the energy of a single water molecule. Adsorption energy is usually negative. The smaller the value, the more stable the adsorption.

[0045] Step 4: Add rare earth elements to specific locations in the unit cell model optimized in Step 3 to obtain the doped iron unit cell structure. Optimize the doped structure using the same optimization method and parameter settings as in Step 3 to obtain a stable structure. Add the optimized water molecules to the surface of the optimized doped iron unit cell at an appropriate height above the appropriate location. Optimize the structure to find the optimal adsorption site and calculate the adsorption energy.

[0046] In a specific implementation, rare earth elements are doped into the surface layer of the optimized surface model. This example uses substitution doping as an example to optimize the structure of the doped surface model. After the optimization is completed, the optimized water molecules are added to a certain height above the optimized doped surface model. Similarly, water molecules may have different adsorption sites. By adsorbing water molecules at these locations and comparing the adsorption energies, the optimal adsorption site is determined. The adsorption energy results of water molecules at different adsorption sites on the iron surface model after doping are shown in Table 1. It can be seen that for the systems before and after doping, the minimum adsorption energy is obtained at the top position, indicating that water molecules tend to adsorb at the top position.

[0047] Step 5: Based on the stable adsorption structure in step 4, first-principles molecular dynamics calculations are performed at different temperatures to analyze the changes in the adsorption of water molecules on the surface as the temperature increases.

[0048] In the specific implementation, the adsorption model after rare earth element doping obtained in step 4 was used as a prototype, and molecular dynamics calculations were performed using Materials Studio software at temperatures of 100K, 300K, and 450K to observe the changes in the adsorption of water molecules on the surface with changes in temperature.

[0049] Step 6: Perform electronic performance calculations and analyze the adsorption mechanism and changes in surface properties after adsorption based on the calculation results.

[0050] In the specific implementation, the bader charge, differential charge, and state density calculations are performed on the final adsorption model obtained in steps 3 and 4. The bader charge and differential charge results are used to observe the transfer of electrons during the adsorption process, and the changes in bonding properties before and after adsorption are analyzed based on the state density results. The differential charge density calculation formula is:

[0051] Δρ=ρ AB –ρ A –ρ B , (3)

[0052] Where Δρ is the differential charge density, ρ AB is the charge density of the adsorption system after stable adsorption, ρ A is the charge density of the surface model before adsorption, ρ B is the charge density of water molecules.

[0053] Figure 5 This is a differential charge density diagram of a typical example. The blue part in the figure represents charge dissipation, and the yellow part represents charge accumulation. It can be seen that the water molecules lose electrons and the neighboring iron atoms gain electrons.

[0054] Table 1

[0055]

[0056] In the above embodiments, the adsorption of water molecules on the surface of rare earth element-doped iron was studied from a computational perspective, which provided a data basis for studying the effect of water molecules adsorbed on the metal surface on the metal properties, and further fundamentally elucidated the mechanism of corrosion, laying the foundation for solving the corrosion problem of steel materials.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron, characterized in that: The method comprises: Establish the crystal unit cell structure of metallic iron, optimize the lattice parameters of the unit cell, and obtain the lattice parameters of the stable unit cell; Based on the stable unit cell, a structural model of the surface to be calculated is established, and the surface energy is calculated using the first-principles calculation method; Optimize the structure of water molecules, add the optimized water molecules to a certain height above the surface layer of the iron surface model, optimize the structure, find the best adsorption site, and calculate the adsorption energy; Rare earth elements are doped into the surface model to obtain the doped iron unit cell structure. Optimized water molecules are added to a certain height above the surface of the iron unit cell structure, and the structure is optimized to find the optimal adsorption site and calculate the adsorption energy. Based on the final adsorption model after doping and combined with molecular dynamics methods, the changes in the adsorption energy and adsorption sites of water molecules with increasing temperature are calculated; Analyze the electron transfer and surface bonding changes after water molecule adsorption through electronic property calculations; Wherein, the calculation formula of the surface energy is: E surf =(E slab –nE bulk ) / 2A; Among them, E surf is the surface energy, E slab is the total energy of the surface model, E bulk is the energy of a single atom of the iron unit cell, the value of n is equal to the total number of atoms in the surface model, and A is the surface area of the surface of the model under study; The calculation formula of the adsorption energy is: AND ad =And total -AND slab -AND H2O , Among them, E ad is the adsorption energy, E total is the total energy of the adsorption system, E slab is the total energy of the surface model, E H2O is the energy of a single water molecule.

2. The method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron according to claim 1, characterized in that: Combined with molecular dynamics methods, the changes in the adsorption energy and adsorption sites of water molecules with increasing temperature are calculated, including: molecular dynamics calculations using Materials Studio software at temperatures of 100K, 300K, and 450K to observe the changes in the adsorption of water molecules on the surface with changes in temperature.

3. The method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron according to claim 1, characterized in that: After establishing the structural model of the surface to be calculated, the method further includes: adding a vacuum layer as needed.

4. The method for calculating the adsorption performance of water molecules on the surface of rare earth element-doped iron according to claim 3, characterized in that: Before establishing the structural model of the surface to be calculated, it also includes: taking the number of atomic layers and the vacuum layer thickness as independent variables and the surface energy as the dependent variable, performing a convergence test on the vacuum layer thickness and the number of atomic layers.

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