A high-throughput design method for crystal structure of ternary nitrogen-rich energetic materials under high pressure

Abstract

The present invention belongs to the field of energetic materials technology and specifically discloses a high-throughput design method for the crystal structure of ternary nitrogen-rich energetic materials under high pressure. Based on electron counting rules, the specific dominant element components of the ternary energetic materials are constructed, and a dominant structure search method is established within the framework of structure search. The method comprises the following steps: determining the search components; structural search; convex hull plot calculation; energy density and mass density assessment; structural screening; stability assessment; electronic structure analysis; and detonation performance assessment. The present invention utilizes the above-mentioned high-throughput design method for the crystal structure of ternary nitrogen-rich energetic materials under high pressure. Within the extremely large search space of ternary compounds, the search scope is greatly narrowed, the search accuracy and efficiency for specific component ratios are improved, and the time and computational resource costs of crystal structure design for ternary nitrogen-rich energetic materials are significantly reduced.

Description

Technical Field

[0001] The present 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 between condensed matter physics and chemistry. Energetic materials are a type of special material that, when stimulated by external stimuli, rapidly release large amounts of heat and gas through their own redox reactions. They are high-energy-density, high-power special materials that can rapidly decompose through self-oxidation-reduction processes in a very short period of 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, an extreme experimental condition and a crucial thermodynamic parameter for regulating the structure of matter, plays a crucial role in the study of energetic materials. In recent years, with the advancement of high-pressure technology, high pressure has become a key approach to break through the physical coupling relationships of traditional CHON energetic materials. Polynitrogen energetic materials synthesized using high-pressure methods lack toxic nitro groups and produce cleaner decomposition products, making them a prime example of the next generation of energetic materials. High pressure offers a natural advantage in promoting the conversion of N≡N triple bonds to N≡N single bonds. This is because the N≡N triple bond increases in energy more rapidly during compression than the N≡N single bond, resulting in the spontaneous formation of N≡N single bond energetic structures under high pressure. However, the extremely stringent synthesis conditions for polymeric nitrogen energetic materials under high pressure (pressures greater than 100 GPa and temperatures greater than 2000 K) have limited their development.

[0004] Faced with the challenges of synthesizing polymeric nitrogen energetic materials, researchers have discovered that doping polymeric nitrogen energetic materials with a small amount of impurity atoms, forming nitrogen-rich energetic materials, can effectively reduce the synthesis conditions. However, these impurity atoms are not only energy-free but also have a large relative atomic mass, significantly reducing the material's energy density and detonation performance.

[0005] In order to balance the structural stability, energy density and detonation performance, people turn to the ternary system of CO+N, that is, the formation of strong covalent single bond in the material and the decomposition product is all gas. Different element ratio has great influence on the high pressure structure of C, N and O ternary energetic material, and there are infinite element ratios in principle, and it is like finding a needle in a haystack to carry out a large number of structure searches under any element ratio. Therefore, a set of physical rules is urgently needed for the element ratio of multi-element nitrogen-rich energetic material to constrain the search ratio, reduce the amount of calculation, and maximize the accuracy of the search component element ratio.

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

[0007] The purpose of the present application is to provide a high-throughput design method for the crystal structure of ternary nitrogen-rich energetic materials under high pressure. The electron counting rule is added to the high-throughput design of the crystal structure of ternary nitrogen-rich energetic materials under high pressure, the element search ratio of the advantage structure is determined, a large number of invalid search calculations are avoided, the rationality of the search ratio is improved, and the design efficiency and scientificity are improved. 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 purpose, the present application provides a high-throughput design method for the crystal structure of ternary nitrogen-rich energetic materials under high pressure, which is based on the electron counting rule to construct specific advantage element components of ternary energetic materials, and establishes an advantage structure search method within the framework of structure search, including the following steps:

[0009] S1, determine the search component, based on the electron counting rule, determine the chemical ratio of the crystal structure of the ternary system, for the ternary nitrogen-rich energetic material C x N y O z system, C as a donor, provides 4 valence electrons, N and O as acceptors, respectively gets 3 and 2 valence electrons, under the constraint of the electron counting rule, the structure ratio should satisfy 4x=3y+2z. By solving the integer solution of the equation, a series of ratios can be obtained;

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

[0011] S3, convex hull graph calculation, taking the most stable single-phase C, O2, N2 under high pressure as the end point of the ternary convex hull graph, calculating the convex hull graph of the ternary compound, analyzing the distance E of the different structure components from the most stable solid line of the convex hull graph under different pressures hull ; selecting the structure with convex energy E hull <0.1 eV / atom as the next step research object.

[0012] S4, energy density and mass density evaluation, obtaining the crystal structure file, performing higher precision optimization under normal pressure to obtain the energy and crystal structure under normal pressure, calculating the mass density according to the lattice constant and relative atomic mass; designing and calculating the decomposition product energy according to the oxygen balance theory, and calculating the energy density;

[0013] S5, structure screening, screening the crystal structure with mass density greater than 1.64 g / cm 3 and energy density greater than 4.30 kJ / g, and further optimizing the structure using first-principle calculation software to improve the precision;

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

[0015] S7, electronic structure analysis, calculating the energy band structure, state density, charge localization function, Bader charge of the material, analyzing the structure stability and energy density potential, and screening the crystal structure with non-magnetic, large band gap, stable chemical bond and energy;

[0016] S8, detonation performance evaluation, calculating the detonation pressure and detonation velocity of the screened structure by Kamlet-Jacobs empirical equation, and obtaining new ternary energetic materials 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, the first-principles calculation software package VASP is used for higher-precision optimization.

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

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

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

[0023] 2. The present application successfully searches a series of crystal structures that meet the electronic counting rules through practice of the C x N y O z system, with the help of the MAGUS software. 11 , C 10 N2O 17 are all C-N and C-O single bond structures, which meet the electronic structure rules, i.e. all valence electrons of cations are given to anions, which meets the physical expectation of electronic structure.

[0024] The technical solutions of the present application will be further described in detail below with the help of the accompanying drawings and examples. DETAILED DESCRIPTION

[0025] Figure 1 is a flowchart of the present application based on the electronic counting rules to explore the advantage stable structure of ternary nitrogen-rich energetic materials;

[0026] Figure 2 is a crystal structure diagram of C, N and O advantage ternary energetic material designed based on the electronic counting rules of the present application;

[0027] Figure 3 is a band structure diagram of C, N and O advantage ternary energetic material designed based on the electronic counting rules of the present application;

[0028] Figure 4 is a convex hull diagram of C, N and O ternary energetic material obtained at 20 GPa high pressure based on the electronic counting rules of the present application;

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

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

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

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

[0033] Figure 9 is a simulation result diagram of a charge localization function of a ternary energetic material of C, N and O obtained by the present application based on the electron counting rule;

[0034] Figure 10 is a simulation result diagram of a molecular dynamics of a ternary energetic material of C, N and O obtained by the present application based on the electron counting rule. DETAILED DESCRIPTION

[0035] The technical solutions of the present application are further described below by means of the accompanying drawings and examples.

[0036] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meanings understood by those skilled in the art to which the present application belongs.

[0037] Example 1

[0038] A high-throughput design method for a crystal structure of a ternary nitrogen-rich energetic material under a high pressure, as shown in Figure 1 based on the electron counting rule to construct a specific advantage element component of a multi-element energetic material, and an advantage structure search method is established in the framework of structure search, including the following steps:

[0039] S1, determining a search component. Based on the electron counting rule, the chemical ratio of the ternary system crystal structure to be studied is determined. For a ternary nitrogen-rich energetic material C x N y O z(x, y, z are integers) system, C as an electron donor, providing 4 valence electrons, N, O as an electron donor, respectively, 3 core 2 valence electrons, so as to meet the electron counting rules, the structure ratio should meet 4x = 3y + 2z. By solving the integer solution of the equation, a series of ratios C2N2O, C3N2O3, C4N2O5, C5N2O7, C5N4O4, C5N6O, C6N2O9, C7N2O 11 , C9N2O 15 , C 10 N2O 17 , etc.

[0040] S2, structure search. Use structure search software MAGUS to search the crystal structure of the chemical ratio determined in step S1 under high pressure (20 GPa, 40 GPa, 60 GPa, 80 GPa, 100 GPa), select the 50 structures with lower energy under each component, and use the first principle calculation software package to optimize with higher precision, select the structure with the lowest energy for the next step analysis;

[0041] S3, Convex hull diagram (ternary convex hull curve) calculation. Take the most stable single phase C, O2, N2 under high pressure (20 GPa, 40 GPa, 60 GPa, 80 GPa, 100 GPa) as the end point of the ternary convex hull diagram, calculate the convex hull diagram of the ternary compound, analyze the distance E hull of the most stable solid line of the convex hull diagram formed by different structure components under different pressures (20 GPa, 40 GPa, 60 GPa, 80 GPa, 100 GPa), select the structure with convex energy E hull <0.1 eV / atom as the next step of 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, and the mass density is further calculated according to the lattice constant and relative atomic mass; according to the oxygen balance theory, the decomposition product energy is designed and calculated, and the energy density is calculated;

[0043] S5, structure screening, screen the crystal structure with mass density and energy density greater than TNT (mass density 1.64 g / cm 3 , energy density 4.30 kJ / g), and further optimize the structure using the first principle calculation software;

[0044] S6. Stability Assessment. Each screened structure is evaluated for kinetic and thermodynamic stability by expanding the cell to approximately 100 atoms and performing a 10 ps molecular dynamics simulation at room temperature (300 K) using the NVT ensemble at atmospheric pressure. The simulated structure is analyzed: if the structural framework can restore its pre-simulation structural characteristics after optimization, or if the total energy of the system fluctuates only around the equilibrium position during the simulation, the structure is considered stable.

[0045] S7. Electronic structure analysis. Use the VASP software package to calculate the material's band structure, density of states, charge localization function, and Bader charge. Analyze the structural stability and energy density potential, and select crystal structures that are non-magnetic, have large band gaps, and are chemically stable and energetic.

[0046] S8. Detonation Performance Evaluation: Using the Kamlet-Jacobs (KJ) empirical equation, we calculated and screened the detonation pressure and detonation velocity of the structure, identifying a novel ternary energetic material with excellent performance, both of which far exceeded those of TNT.

[0047] After C x N y O z Through systematic practice, with the help of MAGUS software, we have successfully searched for a series of crystal structures that meet the electron counting rule. Figure 2 As shown: C5N4O4, C6N2O9, C7N2O 11 、C 10 N2O 17 They are all CN and CO single bond structures, and these structures all meet 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 that they can exist stably under high pressure, while the non-black points represent that they cannot exist stably. The redder the color, the less stable it is. 11 、P1-C 10 N2O 17 Equistructural convex hull energy E hull <0.1eV / atom, which is a stable structure. Bader charge calculation results show that all the valence electrons of the cations in the compound structure are donated to the anions, which is consistent with the expected conjecture. Figure 8 As shown in the design framework of the electron counting rule, the electronic structure of the designed structure is all shown to be an insulator, which has the electronic structure advantages of highly insensitive energetic materials. Figure 9As shown, the results of the charge localization function calculation under normal pressure show that the chemical bonds of all structures exhibit strong covalent bond characteristics, exhibiting stable covalent structures, which are more advantageous than metal nitrogen-rich energetic materials in terms of structural stability. Figure 10 As shown, the results of the molecular dynamics simulation show that the total energy of each structure system only fluctuates around the equilibrium position, without significant upward or downward trend, indicating that these structures have good structural stability at normal temperature and pressure.

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

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

[0051] Structure ρ (g / cm 3 )]]> E d (kJ / g)]]> V d (km / s) P d (GPa) [P1-C5N4O4] 3.48 4.41 11.62 81.90 [P1-C6N2O9] 3.15 4.61 10.59 65.43 [P1-C7N2O 11 ]]> 3.23 5.31 11.95 84.24 [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, and P d is the detonation pressure.

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

[0054] Therefore, the above-mentioned high-throughput design method of crystal structure of ternary nitrogen-rich energetic material under high pressure adds the electron counting rule in the high-throughput design of crystal structure of ternary nitrogen-rich energetic material under high pressure, determines the element search ratio of the advantage 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] It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can still be modified or replaced equivalently, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

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 composition of ternary energetic materials based on electron counting rules and establishes a dominant structure search method within the framework of structure search, characterized by: 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, while 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 integers x, y, and z, a series of ratios can be obtained. S2. Structure search: Use structure search software to search for the crystal structure of the chemical ratio determined in step S1 under high pressure. Select 50 structures with lower energy for each component and use first-principles calculation software package for higher precision optimization. Select the structure with the lowest energy for the next step of analysis. S3. Convex hull calculation: Take the most stable single phases C, O2, and N2 under high pressure as the endpoints of the ternary convex hull diagram, calculate the convex hull diagram of the fitted 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 at different pressures. hull ; Select the convex hull energy E hull The structures with a value < 0.1eV / atom will be the next research targets; 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. Based on the lattice constant and relative atomic mass, the mass density is further calculated. Design and calculate the decomposition product energy 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 densities greater than 4.30 kJ / g, and further structural optimization of these structures using first-principles calculation software to improve accuracy; S6. Stability assessment: Dynamic and thermodynamic stability assessments are performed on each screened structure by expanding the cell to about 100 atoms and performing 10 ps molecular dynamics simulations at room temperature and atmospheric pressure using an NVT ensemble to analyze the simulated structure. S7. Electronic structure analysis: calculate the material's band structure, state density, charge localization function, and Bader charge, analyze the structural stability and energy density potential, and screen for non-magnetic, large band gap, stable chemical bond, and energetic crystal structures. 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, the first principles calculation software package VASP is used to perform higher precision optimization.

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, density of states, charge localization function, and Bader charge of the material.

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