High-throughput design method for crystal structure of ternary nitrogen-rich energetic material under high pressure

Abstract

The invention belongs to the technical field of energetic materials, and particularly discloses a high-throughput design method for a crystal structure of a ternary nitrogen-rich energetic material under high pressure, which is characterized in that specific dominant element components of the ternary energetic material are constructed based on an electronic counting rule, and a dominant structure search method is established in a structure search framework. Comprising the following steps: determining search components; searching a structure; calculating a convex hull graph; evaluating energy density and mass density; structure screening; evaluating the stability; analyzing an electronic structure; and evaluating detonation performance. According to the high-throughput design method for the crystal structure of the ternary nitrogen-rich energetic material under the high pressure, the search range is greatly narrowed in an extremely large search space phase of a ternary compound, the search precision and the search efficiency under specific proportioning components are improved, and the high-throughput design method for the crystal structure of the ternary nitrogen-rich energetic material under the high pressure is realized. And the crystal structure design time cost and the computing resource cost of the ternary nitrogen-rich energetic material are greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of energetic materials, and in particular to a high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure. Background Art

[0002] The study of the physical properties of energetic materials is an interdisciplinary research field of condensed matter physics and chemistry. Energetic materials are a type of special material that rapidly releases a large amount of heat and gas through its own redox reaction when stimulated by external stimuli. They are high-energy density, high-power special materials that can rapidly decompose through the self-oxidation-reduction process in a very short time. They are widely used in high-energy explosives, propellants, military weapons, and pyrotechnics. There are extremely serious physical coupling relationships in the performance physical quantities of energetic materials (mass density, energy density, amount of released gas, structural stability). How to break through these coupling relationships and significantly improve the physical properties of energetic materials is a scientific problem that needs to be urgently solved in the current development of energetic materials.

[0003] Pressure is an extreme experimental condition and an important thermodynamic parameter for regulating the structure of matter. It plays an important role in the research of energetic materials. In recent years, with the development of high-pressure technology and science, high pressure has gradually become an important technical method to break through the physical coupling relationship of traditional CHON energetic materials. The polymerized nitrogen energetic materials synthesized by high-pressure methods do not contain toxic nitro groups and their decomposition products are cleaner. They are typical representatives of the next generation of energetic materials. High pressure has a natural advantage in promoting the conversion of N≡N triple bonds to NN single bonds. This is because the energy of N≡N triple bonds rises faster than that of NN single bonds during compression, so NN single bond energetic structures will spontaneously form under high pressure. However, the synthesis conditions of polymerized nitrogen energetic materials under high pressure are extremely harsh (pressure greater than 100GPa and temperature greater than 2000K), which limits the development of polymerized nitrogen energetic materials.

[0004] Faced with the challenges of the synthesis conditions of polymerized nitrogen energetic materials, people have found that doping a small amount of impurity atoms in polymerized nitrogen energetic materials to form nitrogen-rich energetic materials can effectively reduce the synthesis conditions of the materials. However, these impurity atoms not only do not contain energy, but also have a large relative atomic mass, which will significantly reduce the energy density and detonation performance of the materials.

[0005] In order to take into account structural stability, energy density and detonation performance, people turned their research objects to the ternary system of CO+N, that is, a strong covalent single bond is formed inside the material, and the decomposition products are all gases. Different element ratios have a great influence on the high-pressure structure of C, N, and O ternary energetic materials. In principle, there are infinitely many ratios of the three elements. Carrying out a large number of structural searches under any element ratio is tantamount to looking for a needle in a haystack. Therefore, in the element ratio of multi-component nitrogen-rich energetic materials, it is urgent to propose a set of physical rules to constrain the search ratio, while reducing the amount of calculation and ensuring the accuracy of the search component element ratio to the greatest extent.

[0006] The electron counting rule is an effective physical rule for designing classical semiconductors. It was first proposed in 1989 and is used to design the ratio of elements in new semiconductor structures. For example, Al usually provides 3 valence electrons, showing +3 valence, and N usually obtains 3 electrons, showing -3 valence. Therefore, the anions and cations of the AlN component all satisfy the octet rule, forming a very stable semiconductor structure. This rule has also been used to design new two-dimensional semiconductor structures in recent years. At present, this set of rules has not been introduced in the field of energetic material structure design. Summary of the invention

[0007] The purpose of the present invention is to provide a high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure, add electron counting rules to the high-throughput design of the crystal structure of a ternary nitrogen-rich energetic material under high pressure, determine the element search ratio of the dominant structure, avoid a large number of invalid search calculations, improve the rationality of the search ratio, and enhance the design efficiency and scientificity. A series of new ideal energetic crystal structures with ultra-high mass density, moderate energy density, and certain stability can be obtained. It has important research significance for exploring the crystal characteristics and formation mechanism of multi-element nitrogen-rich energetic materials.

[0008] To achieve the above objectives, the present invention provides a high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure, constructs a specific dominant element component of the ternary energetic material based on the electron counting rule, and establishes a dominant structure search method within the framework of the structure search, comprising the following steps:

[0009] S1. Determine the search components and determine the chemical ratio of the ternary system crystal structure based on the electron counting rule. For the ternary nitrogen-rich energetic material C x N y O z In the system, C acts as an electron donor, providing 4 valence electrons, and N and O act as electron acceptors, obtaining 3 and 2 valence electrons respectively. Under the constraints of the electron counting rule, the structural ratio should satisfy 4x=3y+2z. By solving the equation for the integer solutions of x, y, and z, a series of ratios can be obtained;

[0010] S2, structure search, using structure search software to search the crystal structure of the chemical ratio determined in step S1 under high pressure, select 50 structures with lower energy under each component, use first principle calculation software package to perform higher precision optimization, and select the structure with the lowest energy for the next step of analysis;

[0011] S3, convex hull calculation, taking the most stable single phase C, O2, N2 under high pressure as the endpoints of the ternary convex hull diagram, calculate the convex hull diagram of the ternary compound, and analyze the distance E from the most stable solid line of the convex hull diagram to the formation enthalpy of different structural components under different pressures. hull ; Select the convex hull energy E hull The structure with the voltage <0.1eV / atom will be the next research object.

[0012] S4, energy density and mass density evaluation, the obtained crystal structure file is optimized with higher precision at normal pressure to obtain the energy and crystal structure at normal pressure, and the mass density is further calculated based on the lattice constant and relative atomic mass; the decomposition product energy is designed and calculated based on the oxygen balance theory to obtain the energy density;

[0013] S5. Structural screening: the mass density is greater than 1.64 g / cm 3 and crystal structures with energy density greater than 4.30 kJ / g, and further structural optimization of these structures using first-principles calculation software to improve accuracy;

[0014] S6. Stability evaluation: The dynamic and thermodynamic stability of each screened structure is evaluated by expanding the cell to about 100 atoms and performing a 10ps molecular dynamics simulation at room temperature and normal pressure using the NVT ensemble. The simulated structure is analyzed: if the structural skeleton can restore the structural characteristics before the simulation after structural optimization, or if the total energy of the system only fluctuates around the equilibrium position during the computational simulation, the structure is considered stable.

[0015] S7. Electronic structure analysis, calculate the material's band structure, state density, charge localization function, Bader charge, analyze the structural stability structure, energy density potential, and screen to obtain non-magnetic, large band gap, stable chemical bond and energetic crystal structure;

[0016] S8. Detonation performance evaluation: Through the Kamlet-Jacobs empirical equation, the detonation pressure and detonation velocity of the structure are calculated and screened to obtain a new type of ternary energetic material with excellent detonation pressure and detonation velocity performance.

[0017] Preferably, in step S2, the structure search software is MAGUS.

[0018] Preferably, in step S2, the high pressure is 20 GPa, 40 GPa, 60 GPa, 80 GPa, or 100 GPa.

[0019] Preferably, in step S4, a first-principles calculation software package VASP is used to perform optimization with higher precision.

[0020] Preferably, in step S7, the VASP software package is used to calculate the band structure, state density, charge localization function and Bader charge of the material.

[0021] The advantages and beneficial effects of the present invention using the above-mentioned high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure are:

[0022] 1. The present invention greatly narrows the search range in the extremely large search space of ternary compounds, improves the search accuracy and efficiency under specific ratio components, and greatly reduces the time cost and computing resource cost of crystal structure design of ternary nitrogen-rich energetic materials.

[0023] 2. The present invention is carried out through C x N y O z Through the practice of the system, with the help of MAGUS software, a series of crystal structures that meet the electronic counting rule ratio were successfully searched, including C5N4O4, C6N2O9, C7N2O 11 , C 10 N2O 17 All of them are CN and CO single bond structures, and these structures all satisfy the electronic structure rules, that is, all the valence electrons of the cation are given to the anion, which is in line with the physical expectations of the electronic structure.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the present invention, based on the electron counting rule, to explore the advantageous stable structure of ternary nitrogen-rich energetic materials;

[0026] Figure 2 This is a crystal structure diagram of a C, N, O dominant ternary energetic material designed based on the electron counting rule of the present invention;

[0027] Figure 3 This is the energy band structure diagram of the C, N, O dominant ternary energetic material designed by the present invention based on the electron counting rule;

[0028] Figure 4 It is the convex hull diagram of the C, N, O ternary energetic material obtained under a high pressure of 20 GPa based on the electron counting rule of the present invention;

[0029] Figure 5 It is the convex hull diagram of the C, N, O ternary energetic material obtained under a high pressure of 40 GPa based on the electron counting rule of the present invention;

[0030] Figure 6 It is the convex hull diagram of the C, N, O ternary energetic material obtained under a high pressure of 60 GPa based on the electron counting rule of the present invention;

[0031] Figure 7 It is the convex hull diagram of the C, N, O ternary energetic material obtained under 80 GPa high pressure based on the electron counting rule of the present invention;

[0032] Figure 8 It is the convex hull diagram of the C, N, O ternary energetic material obtained under a high pressure of 100 GPa based on the electron counting rule of the present invention;

[0033] Fig. 9 The simulation result diagram of the charge localization function of the C, N, O dominant ternary energetic material obtained by the present invention based on the electron counting rule;

[0034] Fig.10 This is a diagram of the molecular dynamics simulation results of the C, N, O dominant ternary energetic material obtained by the present invention based on the electron counting rule. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0036] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0037] Example 1

[0038] A high-throughput design method for the crystal structure of ternary nitrogen-rich energetic materials under high pressure, such as Figure 1 As shown, the specific dominant element components of multi-element energetic materials are constructed based on the electron counting rule, and a dominant structure search method is established within the framework of structure search, including the following steps:

[0039] S1. Determine the search component. Based on the electron counting rule, determine the chemical ratio of the ternary system crystal structure to be studied. For the ternary nitrogen-rich energetic material C x N y O z(x, y, z are all integers) system, C as an electron donor, provides 4 valence electrons, N, O as electron acceptors, respectively get 3 nuclei and 2 valence electrons, so to meet the electron counting rule, the structural ratio should meet 4x = 3y + 2z. By solving the integer solution of the equation, a series of ratios can be obtained: C2N2O, C3N2O3, C4N2O5, C5N2O7, C5N4O4, C5N6O, C6N2O9, C7N2O 11 、C9N2O 15 , C 10 N2O 17 wait.

[0040] S2. Structure search. The crystal structure of the chemical ratio determined in step S1 was searched under high pressure (20 GPa, 40 GPa, 60 GPa, 80 GPa, 100 GPa) using the structure search software MAGUS. 50 structures with lower energy were selected for each component and optimized with higher precision using the first principle calculation software package. The structure with the lowest energy was selected for the next step of analysis.

[0041] S3. Convex hull plot (ternary convexhull curve) calculation. The most stable single phases C, O2, and N2 under high pressure (20GPa, 40GPa, 60GPa, 80GPa, and 100GPa) are used as the endpoints of the ternary convex hull plot. The convex hull plot of the ternary compound is calculated and fitted. The formation enthalpy of different structural components under different pressures (20GPa, 40GPa, 60GPa, 80GPa, and 100GPa) is analyzed. The distance E from the most stable solid line of the convex hull plot hull , select the convex hull energy E hull The structure with the voltage <0.1eV / atom will be the next research object.

[0042] S4. Energy density and mass density evaluation. The obtained crystal structure file is optimized with higher precision at normal pressure to obtain the energy and crystal structure at normal pressure. The mass density is further calculated based on the lattice constant and relative atomic mass. The energy of the decomposition products is designed and calculated based on the oxygen balance theory to obtain the energy density.

[0043] S5, structural screening, screening to obtain mass density and energy density greater than TNT (mass density 1.64g / cm 3 , energy density 4.30kJ / g) crystal structure, and further optimize these structures using first-principles calculation software to improve accuracy;

[0044] S6. Stability assessment. The dynamic and thermodynamic stability of each screened structure is evaluated by expanding the cell to about 100 atoms and performing a 10ps molecular dynamics simulation at room temperature (300K) using the NVT ensemble at normal pressure. Analyze the structure after simulation: If the structural skeleton can restore the structural characteristics before simulation after structural optimization, or if the total energy of the system fluctuates only around the equilibrium position during the computational simulation, the structure is considered to be stable.

[0045] S7. Electronic structure analysis. Use the VASP software package to calculate the material's band structure, state density, charge localization function, and Bader charge, analyze the structural stability structure, energy density potential, and screen for non-magnetic, large band gap, stable chemical bond, and energetic crystal structures.

[0046] S8. Detonation performance evaluation. The detonation pressure and detonation velocity of the structure are calculated and screened through the Kamlet-Jacobs (KJ) empirical equation, and a new type of ternary energetic material with excellent performance whose detonation pressure and detonation velocity are much greater than TNT is obtained.

[0047] After C x N y O z Through systematic practice, with the help of MAGUS software, a series of crystal structures that meet the electronic counting rule ratios have been successfully searched. Figure 2 As shown: C5N4O4, C6N2O9, C7N2O 11 , C 10 N2O 17 All of them are CN and CO single bond structures, and these structures all satisfy the electronic structure rules.

[0048] After screening, several structures that can be stable in the convex hull graph were obtained, such as Figures 3 to 7 As shown in the figure, the black points represent stable existence under high pressure, while the non-black points represent unstable existence. The redder the color, the less stable it is. P1-C5N4O4, P1-C6N2O9, P1-C7N2O 11 、P1-C 10 N2O 17 Equistructural convex hull energy E hull <0.1eV / atom, which is a stable structure. The Bader charge calculation results show that all the valence electrons of the cations in the compound structure are given to the anions, which is in line with the expected conjecture. Figure 8 As shown in the figure, under the design framework of the electron counting rule, the electronic structures of the designed structures are all shown as insulators, which have the electronic structure advantages of highly insensitive energetic materials. Fig. 9As shown in the figure, these results are all calculated from the charge localization function at normal pressure. The chemical bonds of all structures show strong covalent bond characteristics and a stable covalent structure, which is more advantageous than metal nitrogen-rich energetic materials in terms of structural stability. Fig.10 As shown, the molecular dynamics simulation results show that the total energy of each structural system only fluctuates around the equilibrium position without significant increase or decrease, indicating that these structures have good structural stability at room temperature and pressure.

[0049] Based on the electron counting rule, the multi-component nitrogen-rich energetic materials searched under high pressure significantly surpassed the energy density of all previously reported C, N, and O ternary energetic materials. The results are shown in Table 1. The stable structures under high pressure are significantly more than the nitrogen-rich energetic structures under the previous random ratio.

[0050] Table 1 Comparison of energetic properties of typical ternary energetic materials of C, N and O

[0051] Structure <![CDATA[ρ(g / cm 3 )]]> <![CDATA[E d (kJ / g)]]> <![CDATA[V d (km / s)]]> <![CDATA[P d (GPa)]]> <![CDATA[P1-C5N4O4]]> 3.48 4.41 11.62 81.90 <![CDATA[P1-C6N2O9]]> 3.15 4.61 10.59 65.43 <![CDATA[P1-C7N2O 11 ]]> 3.23 5.31 11.95 84.24 <![CDATA[P1-C 10 N2O 17 ]]> 3.22 7.09 12.91 98.13 TNT 1.64 4.30 6.90 19.00 HMX 1.90 5.70 9.10 39.30 CL-20 1.86 6.70 9.58 42.00

[0052] In Table 1, ρ is the mass density, E d is the energy density, V d is the detonation velocity, P d is the detonation pressure.

[0053] In Table 1, these materials have ultra-high mass density, and their mass density reaches 3.0g / cm 3 Compared with the 1.6-2.0 g / cm 3 The mass density of the candidate materials has been significantly improved. At the same time, the energy density of the candidate materials is greater than that of super TNT (energy density is 4.30 kJ / g), and the detonation pressure and detonation speed are better than those of classic TNT, HMX, and CL-20 energetic materials. This means that they are new energetic materials with superior performance.

[0054] Therefore, the present invention adopts the above-mentioned high-throughput design method of crystal structure of ternary nitrogen-rich energetic materials under high pressure, adds electron counting rules to the high-throughput design of crystal structure of ternary nitrogen-rich energetic materials under high pressure, determines the element search ratio of the dominant structure, avoids a large number of invalid search calculations, improves the rationality of the search ratio, and improves the design efficiency and scientificity. A series of new ideal energetic crystal structures with ultra-high mass density, moderate energy density and certain stability can be obtained, which has important research significance for exploring the crystal characteristics and formation mechanism of multi-element nitrogen-rich energetic materials.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A high-throughput design method for the crystal structure of ternary nitrogen-rich energetic materials under high pressure, which constructs the specific dominant element components of ternary energetic materials based on electron counting rules, and establishes a dominant structure search method within the framework of structure search, characterized in that: The steps include: S1. Determine the search components and determine the chemical ratio of the ternary system crystal structure based on the electron counting rule. For the ternary nitrogen-rich energetic material C x N y O z In the system, C acts as an electron donor, providing 4 valence electrons, and N and O act as electron acceptors, obtaining 3 and 2 valence electrons respectively. Under the constraints of the electron counting rule, the structural ratio should satisfy 4x=3y+2z. By solving the equation for the integer solutions of x, y, and z, a series of ratios can be obtained; S2, structure search, using structure search software to search for the crystal structure of the chemical ratio determined in step S1 under high pressure, selecting 50 structures with lower energy for each component, using first principle calculation software package for higher precision optimization, and selecting the structure with the lowest energy for the next step of analysis; S3, convex hull calculation, taking the most stable single phase C, O2, N2 under high pressure as the endpoints of the ternary convex hull diagram, calculate the convex hull diagram of the ternary compound, and analyze the distance E from the most stable solid line of the convex hull diagram to the formation enthalpy of different structural components under different pressures. hull ; Select the convex hull energy E hull The structures with a value <0.1eV / atom will be the next research object; S4, energy density and mass density evaluation, the obtained crystal structure file is optimized with higher precision at normal pressure to obtain the energy and crystal structure at normal pressure, and the mass density is further calculated based on the lattice constant and relative atomic mass; Design and calculate the energy of decomposition products based on oxygen balance theory, and calculate the energy density; S5. Structural screening: the mass density is greater than 1.64 g / cm 3 and crystal structures with energy density greater than 4.30 kJ / g, and further structural optimization of these structures using first-principles calculation software to improve accuracy; S6. Stability evaluation: The dynamic and thermodynamic stability of each screened structure is evaluated by expanding the cell to about 100 atoms, performing a 10ps molecular dynamics simulation at room temperature using an NVT ensemble at normal pressure, and analyzing the simulated structure. S7. Electronic structure analysis, calculate the material's band structure, state density, charge localization function, Bader charge, analyze the structural stability structure, energy density potential, and screen to obtain non-magnetic, large band gap, stable chemical bond and energetic crystal structure; S8. Detonation performance evaluation: Through the Kamlet-Jacobs empirical equation, the detonation pressure and detonation velocity of the structure are calculated and screened to obtain a new type of ternary energetic material with excellent detonation pressure and detonation velocity performance.

2. The high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure according to claim 1, characterized in that: In step S2, the structure search software is MAGUS.

3. The high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure according to claim 1, characterized in that: In step S2, the high pressure is 20 GPa, 40 GPa, 60 GPa, 80 GPa, and 100 GPa.

4. The high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure according to claim 1, characterized in that: In step S4, a first-principles calculation software package VASP is used to perform optimization with higher precision.

5. The high-throughput design method for the crystal structure of a ternary nitrogen-rich energetic material under high pressure according to claim 1, characterized in that: In step S7, the VASP software package is used to calculate the band structure, state density, charge localization function, and Bader charge of the material.

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