Crystal structure design and physical property evaluation method of magnetic copper-based nitrogen-rich energetic material

Abstract

The invention discloses a crystal structure design and physical property evaluation method of a magnetic copper-based nitrogen-rich energetic material. The method comprises the following steps: assembling # imgabs 0 #, # imgabs 1 #, # imgabs 2 # and # imgabs 3 # anions and a Cu < 2 + > cation structure; optimizing high-throughput structures in the same spinning direction, and screening 10 structures with the lowest energy under each component; optimizing structures in different spin directions, and determining magnetic sequence characteristics and magnetic moments of 10 structures with the lowest energy under each component; performing stability evaluation on the structures, eliminating unstable structures, and performing energetic property evaluation on stable structures; evaluating energetic properties, eliminating structures with poor properties, and taking structures with good properties as crystal structures of the target copper-based nitrogen-rich energetic material; and carrying out magnetic mechanism analysis and comprehensive physical property analysis on the target copper-based nitrogen-rich energetic material. The technical problem of predicting the crystal structure of the magnetic copper-based nitrogen-rich energetic material is solved. The stable crystal structure of the copper-based nitrogen-rich energetic material is obtained, the energy density limit of the known copper-based nitrogen-rich energetic material is broken through, and the physical property evaluation method of the energetic material containing the spinning electrons is illustrated. The method is of great significance to the design of a nitrogen-rich energetic material crystal structure containing spin electrons.

Description

Technical Field

[0001] The invention belongs to the technical field of computational physics of energetic materials, and in particular relates to a crystal structure design and physical property evaluation method of a magnetic copper-based nitrogen-rich energetic material. Background Art

[0002] Energetic materials are compounds that rapidly release large amounts of energy and gas under external stimulation. They are widely used in military, aerospace, rocket propulsion, and civilian fields. Copper azide (CuN6) is an explosive that was first reported in 1967 and is a highly sensitive, high-energy-density energetic material. It can rapidly trigger an explosive reaction with a relatively small amount of energy input, so it has important applications in the military and industrial explosion fields and is currently a hot research area for energetic materials.

[0003] In CuN6, after the Cu atom loses two valence electrons, the remaining 9 electrons are filled in 5 3d orbitals. Therefore, one 3d orbital is half-filled and unpaired. This electron exhibits the physical characteristics of spin, so from a macroscopic point of view, CuN6 exhibits magnetism. However, the mechanism of the influence of spin electrons on the structural stability and energy density of CuN6 is still unclear. Unpaired electrons show a high spin state, which is beneficial to energy density but not to structural stability. To improve the physical properties of copper-based nitrogen-rich energetic materials, the key is to decouple the contradictory relationship between energy density and structural stability. So far, a series of new magnetic copper-based high-energy compounds have been reported (such as copper-5-nitroimidazole tetrazolium, etc.), which exhibit different physical properties under different coordinated anions. Therefore, exploring the energy density and structural stability of the crystal structure of energetic materials under different coordination configurations of different coordinated anions is the key to breaking through the physical properties of copper-based nitrogen-rich energetic materials.

[0004] Energetic materials with spin electrons usually have low sensitivity, so there are great safety hazards during the experiment. Therefore, the development of energetic materials with spin electrons is relatively slow. In recent years, with the development of density functional theory, first-principles computational simulation has become one of the safer and more efficient methods for the design of crystal structures of energetic materials. However, since the direction of the magnetic moment of energetic materials containing spin electrons is difficult to obtain through high-throughput calculations during the calculation process, the physical mechanism of the magnetic moment generation is difficult to discern. Therefore, the design of the crystal structure of energetic materials is currently limited to non-magnetic materials, and there is still a lack of effective design solutions for the crystal structure of magnetic copper-based nitrogen-rich energetic materials. Summary of the invention

[0005] The present invention discloses a crystal structure design and physical property evaluation method for a magnetic copper-based nitrogen-rich energetic material. By designing a special first-principles crystal structure design method and a physical property evaluation scheme for the crystal structure of a magnetic copper-based nitrogen-rich energetic material, the most stable crystal structures of different magnetic copper-based nitrogen-rich energetic materials are explored, and their structural stability and energy density are calculated, so as to obtain a copper-based nitrogen-rich energetic material that can break through the energy density performance limit of the copper-based nitrogen-rich energetic material.

[0006] The present invention solves the technical problem of crystal structure prediction of magnetic copper-based nitrogen-rich energetic materials, and clarifies the physical mechanism of spin electrons in the energy density and structural stability of energetic materials. At the same time, the crystal structure of the copper-based nitrogen-rich energetic material is obtained to stabilize, breaking through the energy density limit of the known copper-based nitrogen-rich energetic materials. It is of great significance for the crystal structure design of nitrogen-rich energetic materials containing spin electrons.

[0007] Table 1 Typical P2 1 2 1 2 1 -CuN 10 Comparison of properties of copper-based nitrogen-rich energetic materials with known copper-based nitrogen-rich energetic materials In Table 1, ρ is the mass density, Ed is the energy density, E v is the volume energy density.

[0008] The present invention is achieved through the following technical solutions: A method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material comprises the following steps: (1) , , and Nitrogen-rich anions and Cu 2+ Structural assembly of cations; (2) High-throughput structural optimization of the same spin direction, screening the 10 structures with the lowest energy for each component; (3) Optimize the structures in different spin directions and determine the magnetic order characteristics and magnetic moment sizes of the 10 lowest energy structures for each component; (4) Evaluate the stability of the structure, eliminate unstable structures, and evaluate the energetic properties of stable structures; (5) Evaluation of energetic properties, eliminating structures with poor performance, and selecting structures with good performance as the crystal structure of the target copper-based nitrogen-rich energetic material; (6) Conduct magnetic mechanism analysis and comprehensive physical property analysis on the crystal structure of the target copper-based nitrogen-rich energetic material.

[0009] The specific steps of structural assembly are: , , and Nitrogen-rich anions and Cu 2+ The structural assembly of cations was carried out by using the CALYPSO crystal structure search software package. According to the ratio of the charge numbers of anions and cations, a large number of Cu(N3)2, Cu(N5)2 and Cu(N7)2 crystal structures were randomly generated under the constraints of 230 space group symmetries. 30 random structures were generated for each component in each generation, and 300 structures were calculated in 10 generations. Therefore, a total of 1200 crystal structures were generated.

[0010] The specific steps of high-throughput structural optimization with the same spin direction are as follows: during the structural optimization process, the initial magnetic moment of the Cu atoms is set to spin upward, 1,200 structures are subjected to high-throughput structural optimization at the same level of computational accuracy, the optimized structures are energy-ranked, and the top 10 structures with the lowest energy for each component are obtained.

[0011] The specific steps for optimizing structures with different spin directions are as follows: finely optimize the 10 lowest energy structures obtained under each component, set different magnetic orders during the structural optimization process, including ferromagnetic, antiferromagnetic, ferrimagnetic and non-magnetic, and use the lowest energy magnetic order state as the ground state of the structure to determine the magnetic order characteristics and magnetic moment size of each structure.

[0012] The specific steps for evaluating the stability of the structure are: under a certain magnetic order, obtain the phonon spectrum, molecular dynamics, mechanical stability and charge localization function of the 10 lowest energy structures obtained for each component, evaluate the stability of the calculation results, and eliminate structurally unstable structures.

[0013] The energetic property assessment includes the assessment of the mass density and energy density of the structure. The mass density of the material is calculated using the ratio of the total atomic mass to the volume of the atoms in the crystal structure unit cell, the decomposition reaction of the material is designed, and the energy density is calculated by calculating the energy difference between the reactants and the decomposition. Crystal structures with mass density and energy density less than the known copper-based nitrogen-rich energetic materials are eliminated.

[0014] The target copper-based nitrogen-rich energetic material containing spin electrons is obtained, and its crystal structure is P2 1 2 1 2 1 -Cu(N5)2 structure.

[0015] Magnetic mechanism analysis of target copper-based nitrogen-rich energetic materials: Using molecular orbital theory, we analyze P2 1 2 1 2 1 -The magnetic source of high-performance magnetic copper-based nitrogen-rich energetic materials with Cu(N5)2 structure and the analysis of the orbits occupied by spin electrons will be beneficial to further explore the electronic structure, light absorption and other applications of magnetic copper-based nitrogen-rich energetic materials.

[0016] Comprehensive physical property analysis of target copper-based nitrogen-rich energetic materials: By calculating the energy band structure, P2 1 2 1 2 1 -Conductivity of high-performance magnetic copper-based nitrogen-rich energetic materials with Cu(N5)2 structure; By calculating the absorption spectrum, it is revealed P2 1 2 1 2 1 -The maximum light absorption band of Cu(N5)2 structure. Comprehensively evaluate the physical properties and potential application scenarios of the material.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses Cu 2+ Cations and nitrogen-rich anions are used as assembly units of the crystal structure of energetic materials. Through first-principles optimization software, a stable magnetic copper-based nitrogen-rich energetic material crystal structure can be effectively obtained.

[0018] 2. The stable Cu(N5)2 crystal structure obtained by the method of the present invention realizes the magnetic copper-based nitrogen-rich energetic material with the highest nitrogen concentration known so far, and its energy density level reaches 4.05 kJ / g, which is the highest value of copper-based nitrogen-rich energetic materials known so far.

[0019] 3. The present invention adopts the first-principles crystal structure prediction method to obtain the magnetic copper-based nitrogen-rich energetic material, which is safer, has a shorter research cycle and lower research cost than the experimental synthesis method. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flowchart for implementing the present invention; Figure 2 It is an anion and a cation used for assembling magnetic copper-based nitrogen-rich energetic materials; Figure 3 This is a typical magnetic copper-based nitrogen-rich structure diagram generated by CALYPSO and optimized by VASP; Figure 4 for P2 1 2 1 2 1 -Different magnetic properties of Cu obtained by considering different initial magnetic moment directions during the optimization of Cu(N5)2 structure, (a) ferromagnetic; (b) antiferromagnetic 1; (c) antiferromagnetic 2; (d) ferrimagnetic state diagram; Figure 5 for P2 1 2 1 2 1 -Cu(N5)2 structure (a) Crystal orbital Hamiltonian overlap layout function calculation results; (b) Charge localization function calculation results; (c) Phonon spectrum calculation results; (d) Molecular dynamics calculation results diagram; Figure 6 for P2 1 2 1 2 1 -CuN 10 Molecular orbital analysis of the origin of structural magnetic physics; Figure 7 for P2 1 2 1 2 1 -CuN 10 The band structure and absorption spectrum of the structure. DETAILED DESCRIPTION

[0021] The following is combined with Figure 1 -Attached Figure 7 Unless otherwise specified, the technical means used in the specific embodiments of the present invention are methods well known to those skilled in the art.

[0022] If no specific techniques or conditions are specified in the examples, all are conventional methods or are carried out according to the techniques or conditions described in the literature in the field, or according to the product instructions. If no manufacturer is specified for the computing software used, all are conventional products that can be purchased through regular channels.

[0023] Example 1 The flow chart of the present invention is as follows Figure 1 The specific implementation process is as follows: 1. Selection of nitrogen-rich anions. Through searching, the currently known typical nitrogen-rich anions include , , and Four types, such as Figure 2 As shown, the four nitrogen-rich anions are selected to react with Cu with a single electron. 2+ Cations carry out structural assembly.

[0024] 2. Generation of random crystal structures. Using the CALYPSO crystal structure search software package, according to the ratio of anion and cation charges, under the constraints of 230 space group symmetries, and under the ratio of Cu(N3)2, Cu(N5)2, Cu(N6) and Cu(N7)2 components, 30 random structures were generated for each component in each generation, and 300 structures were calculated for 10 generations. Therefore, a total of 1200 crystal structures were generated.

[0025] 3. Screen the 10 structures with the lowest energy for each component. Using the first-principles optimization software VASP, set the initial magnetic moment of the Cu atom to spin up during the structure optimization process. Sort the optimized structures by energy to obtain the top 10 structures with the lowest energy for each component. Typical structures are as follows: Figure 3 shown.

[0026] 4. Determine the magnetic order characteristics. Using the VASP software package, the 10 lowest energy structures obtained under each component are finely optimized. Different magnetic orders are set during the structure optimization process, including ferromagnetic, antiferromagnetic, ferrimagnetic and non-magnetic. Based on the principle of minimum energy, the magnetic order characteristics of each structure are determined. P2 1 2 1 2 1 -Cu(N5)2 structure as an example, Figure 4 As shown, the energy of antiferromagnetic 2 is the lowest. The ferromagnetic state is 30.25 meV / formula higher than the energy of antiferromagnetic 2, the antiferromagnetic state 1 is 29.50eV / formula higher than the energy of antiferromagnetic 2, the ferrimagnetic state is 15.25meV / formula higher than the energy of antiferromagnetic 2, and the non-magnetic state is 128meV / formula higher than the energy of antiferromagnetic 2. Therefore, antiferromagnetic 2 is P2 1 2 1 2 1 -The ground state magnetic moment structure of Cu(N5)2. The strength of each magnetic moment is 0.97μB and the total magnetic moment is 0.00μB.

[0027] 5. Stability evaluation. Using the VASP software package, under a certain magnetic order, the phonon spectra, molecular dynamics, mechanical stability and charge localization function of the 10 lowest energy structures obtained for each component are evaluated for the stability of the calculation results, and the unstable structures are eliminated. P2 1 2 1 2 1 -Cu(N5)2 structure as an example, Figure 5 As shown in the figure, the calculated results of a crystal structure with good stability should have the following characteristics: a. The Hamiltonian overlap layout function of the crystal orbital can evaluate the bonding strength of the material. The Cu-N bond should maintain the ionic bond characteristics, and the integral value of the Hamiltonian overlap layout function of the crystal orbital is less than 3.0 in the entire energy range; while the NN bond inside the nitrogen-rich anion group should maintain a covalent bond, and the integral value of the Hamiltonian overlap layout function of the crystal orbital is greater than 7.0 in the entire energy range; b. The charge localization function can effectively analyze the bonding characteristics inside the crystal structure. For stable structures, the metal and the nitrogen-rich group should show significant ionic bond characteristics, and the charge localization function value between Cu-N tends to be between 0.0 and 0.4. The nitrogen-rich group should maintain significant NN covalent bond characteristics, and the charge localization function value between NN should be greater than 0.7; c. The phonon spectrum of the calculated stable crystal structure has no imaginary frequency, and all vibration frequencies should be greater than 0.0 cm -1 ; d. The first peak of the radial distribution function NN and Cu-N extracted from the molecular dynamics simulation results calculated at room temperature 300K should be clearly separated from the second peak, and the total energy should fluctuate at the equilibrium position without sudden increase or decrease during the simulation. The calculation results show that there are 25 crystal structures of magnetic copper-based nitrogen-rich energetic materials that do not meet the above stability characteristics, and all of them have been eliminated.

[0028] 6. Energy property evaluation. Use the ratio of the total atomic mass to the volume of the atoms in the crystal structure unit cell to calculate the mass density of the material, design the decomposition reaction of the material, and calculate the energy density by calculating the energy difference between the reactants and the decomposition. Eliminate materials with a mass density less than 2.0g / cm 3 , the crystal structure of magnetic copper-based nitrogen-rich energetic materials with a mass energy density of less than 3.84 kJ / g.

[0029] 7. Obtain magnetic copper-based nitrogen-rich energetic materials with stable structure, high mass density and high energy density. P2 1 2 1 2 1 -Cu(N5)2 structure.

[0030] 8. Analysis of magnetic mechanism. Using molecular orbital theory, analyze the magnetic stability mechanism of different coordinated anions and different coordination configurations of Cu, and explore the mechanism of the influence of copper spin electrons on material stability. Figure 6 As shown, P2 1 2 1 2 1 -Cu(N5)2 has a planar four-coordinated structure, so the 4d electrons in Cu are excited to the 4p orbital, and the empty 3d orbital forms a dsp with the empty 4s and 4p orbitals. 2 Orbital hybridization, these hybrid orbitals are The lone pair of electrons is filled to form a strong coordination bond, and the subsequent electron rearrangement, a dsp 2 The electrons in the 4p orbital are transferred to the 4p orbital, resulting in a lower energy crystal structure. 2 track, so P2 1 2 1 2 1 -The spin electronics (magnetism) of the Cu(N5)2 structure also comes from dsp 2 The analysis of the magnetic stability mechanism of different coordinated anions and Cu in different coordination configurations is conducive to further exploring the electronic structure, light absorption and other applications of magnetic copper-based nitrogen-rich energetic materials.

[0031] 9. Comprehensive physical property analysis. The band structure calculation results show that P2 1 2 1 2 1 -Cu(N5)2 exhibits indirect bandgap semiconductor characteristics with a bandgap value of 5.59eV. Both the valence band top and the conduction band bottom are composed of relatively flat Cu spin electrons, and the conductivity is poor. The absorption spectrum shows P2 1 2 1 2 1 -Cu(N5)2 has almost no absorption in the visible light range (380nm~750nm) and is a transparent crystal.

[0032] In summary, the method of the present invention obtains an antiferromagnetic material with poor conductivity, transparency, high mass density and high energy density. P2 1 2 1 2 1-Cu(N5)2 energetic materials.

Claims

1. A method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material, characterized in that: The following steps are involved: (1) , , and Nitrogen-rich anions and Cu 2+ Structural assembly of cations; (2) High-throughput structural optimization of the same spin direction, screening the 10 structures with the lowest energy for each component; (3) Optimize the structures in different spin directions and determine the magnetic order characteristics and magnetic moment sizes of the 10 lowest energy structures for each component; (4) Evaluate the stability of the structure, eliminate unstable structures, and evaluate the energetic properties of stable structures; (5) Evaluation of energetic properties, eliminating structures with poor performance, and selecting structures with good performance as the crystal structure of the target copper-based nitrogen-rich energetic material; (6) Conduct magnetic mechanism analysis and comprehensive physical property analysis on the target copper-based nitrogen-rich energetic materials.

2. The method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material according to claim 1, characterized in that: The specific steps of structural assembly are: , , and Nitrogen-rich anions and Cu 2+ The structural assembly of the cations yielded 300 structures per component under the constraints of 230 space groups, for a total of 1200 crystal structures.

3. The crystal structure design and physical property evaluation method of a magnetic copper-based nitrogen-rich energetic material according to claim 1, characterized in that: The specific steps of high-throughput structural optimization with the same spin direction are as follows: during the structural optimization process, the initial magnetic moment of the Cu atoms is set to spin upward, 1,200 structures are optimized with high throughput, the optimized structures are energy ranked, and the top 10 structures with the lowest energy for each component are obtained.

4. The method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material according to claim 1, characterized in that: The specific steps for optimizing structures with different spin directions are as follows: finely optimize the 10 lowest energy structures obtained under each component, set different magnetic orders during the structural optimization process, including ferromagnetic, antiferromagnetic, ferrimagnetic and non-magnetic, and determine the ground state magnetic order characteristics and magnetic moment size of each structure according to the principle of minimum energy.

5. The method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material according to claim 1, characterized in that: The specific steps for evaluating the stability of the structure are: under the determined magnetic order characteristics, obtain the phonon spectrum, molecular dynamics, mechanical stability and charge localization function of the 10 lowest energy structures obtained under each component, evaluate the stability of the calculation results, and eliminate structurally unstable structures.

6. The method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material according to claim 1, characterized in that: The energetic property assessment includes the evaluation of the mass density and energy density of the structure.

7. The method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material according to claim 1, characterized in that: The crystal structure of the target copper-based nitrogen-rich energetic material is P2 1 2 1 2 1 -Cu(N5)2 structure.

8. The method for crystal structure design and physical property evaluation of a magnetic copper-based nitrogen-rich energetic material according to claim 1, characterized in that: For spin electrons P2 1 2 1 2 1 -Analysis of magnetic mechanism and comprehensive physical properties of Cu(N5)2 crystal structure.

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