Carbon-based nitrogen-rich energetic material crystal structure design method based on functional group assembly under high pressure

Abstract

The invention discloses a carbon-based nitrogen-rich energetic material crystal structure design method based on functional group assembly under high pressure. The method comprises the following steps: (1) carrying out structural assembly on a CN4 functional group unit and an N2 structural unit; (2) structure optimization is carried out under high pressure, and the structure with the lowest energy under each component is reserved; (3) calculating formation energy to obtain a convex hull graph under high pressure; (4) high-pressure stability evaluation: eliminating unstable structures, and performing high-pressure synthesis route evaluation on stable structures; (5) obtaining a structural phase under normal pressure; (6) performing normal-pressure physical property evaluation, eliminating structures with poor normal-pressure stability, and performing performance evaluation on structures with good stability; (7) performance evaluation: eliminating structures with poor performance; and (8) obtaining a structure with good performance, namely obtaining the target carbon-based nitrogen-rich energetic material. According to the method, the problem that a stable phase is difficult to find by searching a crystal structure of the carbon-based nitrogen-rich energetic material is solved, the carbon-based nitrogen-rich energetic material of which the mass density is higher than 2.5 g / cm < 3 > and the energy density is higher than 7.2 kJ / g is obtained, and the performance limit of the known carbon-based nitrogen-rich energetic material is broken through.

Description

Technical Field

[0001] The present invention belongs to the technical field of computational physics of energetic materials, and in particular relates to a method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure. Background Art

[0002] Energetic materials are high-power materials that decompose rapidly under external stimuli and are widely used in explosive materials, rocket propellants, fireworks technology and other fields. In 1912, trinitrotoluene (TNT) was invented as a typical energetic material and became the main component of modern firearms and ammunition. Subsequently, cyclotrimethylene trinitramine (RDX), octogen (HMX), and hexanitrohexaazaisowurtzitane (CL-20) were invented one after another and further used in rockets, missiles and other weapons, promoting the further development of energetic materials. However, these traditional CHON energetic materials containing nitro (-NO2) are usually molecular crystals. The production process is not only toxic, but also has a relatively low atomic stacking density (<2.5g / cm 3 ), and the energy density level is also lower than 7.2 kJ / g, which affects the detonation performance of energetic materials. Therefore, it is urgent to explore new energetic materials.

[0003] Carbon-based nitrogen-rich energetic materials are a new type of environmentally friendly energetic materials. The energy density comes from the NN single bond (bond energy 160 kJ / mol) and N=N double bond (bond energy 418 kJ / mol) in the structure, and the huge bond energy difference of N≡N triple bond (bond energy 954 kJ / mol) is generated during the decomposition process. At present, the CN compounds prepared by chemical synthesis methods have not yet broken through the limits of 6.08 kJ / g and 2.2 g / cm³ in terms of mass and energy density. For example, C2N 16 、C2N 14 、C6N 20 This is mainly because the C=N and N=N double bond structures contained in these compounds have lower connectivity and energy density than the all-single-bond CN and NN structures.

[0004] High-pressure technology has been proven to improve the mass density of carbon-based nitrogen-rich energetic materials. Recent research results show that under high-pressure conditions of 134 GPa, carbon-nitrogen compounds can react with N2 to produce high-density CN2 energetic compounds. However, its synthesis pressure needs to be reduced and its energy density needs to be improved.

[0005] The computational simulation method based on the first principles has become an important research and development tool for energetic materials. At present, the method has been used to predict the performance of CsN5, LiN5, CeN8, CON2, CN 20 However, the system for predicting carbon-based nitrogen-rich energetic materials based on first principles under high pressure is limited to CN20 This is mainly because the N≡N triple bond in N2 is difficult to be activated by carbon under high pressure. Therefore, in the crystal structure search process with atoms as the basic input unit, the completely randomly generated carbon-based nitrogen-rich crystal structure will tend to preferentially generate a structural phase containing N≡N during the structural optimization process under lower synthesis pressure, and induce high-performance carbon-based nitrogen-rich energetic materials that are difficult to produce densely packed under high pressure conditions. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a method for designing the crystal structure of carbon-based nitrogen-rich energetic materials based on functional group assembly under high pressure, which solves the problem that it is difficult to find a stable phase in the crystal structure search of carbon-based nitrogen-rich energetic materials, and obtains a synthesis pressure lower than 60GPa and a mass density higher than 2.5g / cm 3 , carbon-based nitrogen-rich energetic materials with an energy density higher than 7.2kJ / g, breaking through the performance limits of known carbon-based nitrogen-rich energetic materials.

[0007] Table 1 Typical carbon-based nitrogen-rich energetic materials obtained by the present invention ( P 2 / c-CN6 and P 1-CN7) Comparison of properties with other known energetic materials In Table 1, ρ is the mass density, Ed is the energy density, Vd is the detonation velocity, Pd is the detonation pressure.

[0008] The present invention is achieved through the following technical solutions: A method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure comprises the following steps: 1. Structural assembly. The CN4 functional group unit and the N2 structural unit were used to assemble the structure using the structural search software RG2. During the assembly process, the CN4 group was allowed to share the N atom in CN4. Under this strategy, a large number of carbon-based nitrogen-rich random crystal structures of CN2, CN3, CN4, CN5, CN6, and CN7 can be generated.

[0009] 2. Structural optimization under high pressure. A large number of carbon-based nitrogen-rich random crystal structures of CN2, CN3, CN4, CN5, CN6, and CN7 were generated and structurally optimized using the first-principles calculation software VASP at pressures of 10 GPa, 20 GPa, 30 GPa, 40 GPa, 50 GPa, 60 GPa, 70 GPa, 80 GPa, 90 GPa, and 100 GPa. A step-by-step optimization strategy was adopted, with optimization performed three times from low precision to high precision to improve the efficiency of structural optimization.

[0010] 3. Keep the structure with the lowest energy under each component. By reading the energy output by VASP structure optimization, sorting the energy, and screening to obtain the structure with the lowest energy under each pressure point of 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa and 100GPa for each component.

[0011] 4. Calculation of formation energy. By referring to the most stable structure of the reference phase at pressure points of 10 GPa, 20 GPa, 30 GPa, 40 GPa, 50 GPa, 60 GPa, 70 GPa, 80 GPa, 90 GPa and 100 GPa, the formation energy of the most stable carbon-based nitrogen-rich structure at each pressure point is calculated.

[0012] 5. Calculation of convex hull diagram under high pressure. Construct the convex hull diagram of carbon-based nitrogen-rich energetic materials by calculating the formation energy of the most stable carbon-based nitrogen-rich structure at pressure points of 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa and 100GPa. Screen and obtain the stable structural phase with a distance of less than 0.1eV / atom from the solid line in the convex hull diagram, and define it as the dominant carbon-based nitrogen-rich energetic material structural phase with the possibility of synthesis under high pressure.

[0013] 6. High-pressure stability assessment. The stability of the structure in the convex hull diagram is analyzed through phonon spectrum, molecular dynamics, formation mechanism and charge transfer. Unstable structures are eliminated and stable structures are evaluated for high-pressure synthesis routes.

[0014] 7. High-pressure synthesis route evaluation: Calculate the enthalpy difference diagram for the structural phases of advantageous carbon-based nitrogen-rich energetic materials that have the possibility of synthesis under high pressure, and analyze the potential synthesis reactants and synthesis pressure points.

[0015] 8. Obtain the structural phase under normal pressure. By releasing the pressure, the first-principle software VASP is used to optimize the structural phase of the advantageous carbon-based nitrogen-rich energetic material that has the possibility of synthesis under high pressure under normal pressure.

[0016] 9. Physical property evaluation at normal pressure. The first-principle software VASP is used to calculate the charge localization function, charge difference, and group interaction of the stable structural phase at normal pressure, evaluate the structural bonding characteristics, analyze the physical mechanism of structural stability, and explore physical methods to further improve its mass density and energy density. Structures with poor stability at normal pressure are eliminated, and structures with good stability are evaluated for performance.

[0017] 10. Performance evaluation. Calculate the mass density, energy density and mechanical properties of the normal pressure stable structure, use the Kamlet-Jacobs (KJ) equation to evaluate the detonation performance of the normal pressure stable structure, and eliminate the structures with poor performance.

[0018] 11. Obtain a mass density higher than 2.5g / cm 3 , new carbon-based nitrogen-rich energetic materials with energy density higher than 7.2kJ / g.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adopts CN4 units and N2 units as input structures for structural assembly, and utilizes the shear force between CN4 and N2 to more effectively obtain CN2, CN3, CN4, CN5, CN6, and CN7 stable carbon-based nitrogen-rich energetic material crystal structures in the structural optimization process.

[0020] 2. The present invention can obtain a larger number of carbon-based nitrogen-rich energetic material crystal structures with richer components. The constituent unit CN4 has a natural CN single bond characteristic, so it is possible to obtain carbon-based nitrogen-rich energetic materials with higher energy density and greater stacking mass density, which is conducive to breaking through the performance limits of known carbon-nitrogen energetic materials.

[0021] 3. Carbon-based nitrogen-rich energetic materials are obtained based on first-principles calculations and design. This research method is safer than the experimental synthesis method, has a shorter research cycle and lower research costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flowchart for implementing the present invention; Figure 2 The most stable carbon-based structures at 40 GPa are (a) CN2, (b) CN3, (c) CN4, (d) CN5, (e) CN6, and (f) CN7. Figure 3 The high-pressure convex hull diagram of the carbon-based nitrogen-rich energetic material is calculated and obtained for Example 1; Figure 4 For (a) C 2-CN2, (b) I 2 d -CN4, (c) P 2 / c-CN6 and (d) P Phonon spectrum and molecular dynamics calculation results of 1-CN7 structural phase; Figure 5 for P 2 / Enthalpy difference diagram calculation results of c-CN6 structural phase; Figure 6 for P 2 / c-CN6 structure (a) Charge localization function, (b) Charge difference, (c) Schematic diagram of CN4 and N2 shear force, (d)-(h) orbital interaction between CN4 and N2; Figure 7is the energy density value of nitrogen-rich energetic materials that are stable at room temperature under different nitrogen concentrations. DETAILED DESCRIPTION

[0023] 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.

[0024] 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.

[0025] Example 1 The flow chart of the present invention is as follows Figure 1 The specific implementation process is as follows: 1. Structural assembly. The structural unit ratio of m×CN4+n×N2 (m=1, n=0,1,2,3,4) was adopted, and the structural search software RG2 was used for structural assembly. During the assembly process, the CN4 group was allowed to share the N atom in CN4. Therefore, 800 random structures were generated for each component of CN2, CN3, CN4, CN5, CN6, and CN7, totaling 4,800 carbon-based nitrogen-rich random crystal structures.

[0026] 2. Structural optimization under high pressure. The carbon-based nitrogen-rich random crystal structures of these 4200 CN2, CN3, CN4, CN5, CN6, and CN7 were optimized under pressures of 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa, and 100GPa using the first-principles calculation software VASP. A step-by-step optimization strategy was adopted, with optimization from low precision to high precision three times, and the cutoff energy was set to 300eV, 600eV, and 1000eV in turn to improve the efficiency of structural optimization.

[0027] 3. Keep the structure with the lowest energy under each component. By reading the energy output by VASP structure optimization, sorting the energy, and screening to obtain the structure with the lowest energy under each pressure point of 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa and 100GPa for each component. Figure 2 The most stable carbon-based structures of CN2, CN3, CN4, CN5, CN6, and CN7 at 40 GPa are listed.

[0028] 4. Calculation of formation energy. By referring to the most stable structures of the reference phase (α-C3N4 and C2N 16 ), calculate the formation energy of the most stable carbon-based nitrogen-rich structure at each pressure point.

[0029] 5. Calculation of convex hull diagram under high pressure. The convex hull diagram of carbon-based nitrogen-rich energetic materials is constructed by calculating the formation energy of the most stable carbon-based nitrogen-rich structure at pressure points of 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa and 100GPa. Figure 3 ). The convex hull diagram was screened and defined as the dominant carbon-based nitrogen-rich energetic material structure phase with the possibility of synthesis under high pressure. The results show that the most stable CN2 and CN6 structure phases can be found on the solid line of the convex hull diagram at 40 GPa, and the most stable CN2, CN4, CN6 and CN7 structure phases can be found on the solid line of the convex hull diagram at 50 GPa.

[0030] 6. High-pressure stability evaluation: The stable structural phases whose distance from the solid line in the convex hull diagram is less than 0.1 eV / atom are analyzed through phonon spectrum, molecular dynamics, formation mechanism and charge transfer, and the unstable structures are eliminated, and the stable structures are evaluated for the high-pressure synthesis route. Figure 4 Listed C 2-CN2, I 2 d -CN4, P 2 / c-CN6 and P The phonon spectrum and molecular dynamics calculation results of the 1-CN7 structural phase show that they have good kinetic and thermodynamic stability.

[0031] 7. Evaluation of high-pressure synthesis routes. Carbon-based nitrogen-rich energetic materials with the possibility of synthesis under high pressure P The enthalpy difference diagram of 2 / c-CN6 structure phase was calculated, and the results showed that P The synthesis pressure of 2 / c-CN6 phase is C 2-CN2, I 2 d -CN4, P 2 / c-CN6 and P The lowest value is 36.6 GPa in 1-CN7, and the synthetic reactants are α-C3N4 and C2N 16 ( Figure 5 ).

[0032] 8. Obtain the structural phase under normal pressure. By releasing the pressure, the first principle software VASP is used to optimize the structural phase of the advantageous carbon-based nitrogen-rich energetic material with the possibility of synthesis under high pressure, including C 2-CN2, I 2 d -CN4, P 2 / c-CN6 and P 1-CN7 can obtain its crystal structure at normal pressure.

[0033] 9. Physical property evaluation at normal pressure. Calculated using first principle software VASP P Charge localization function, charge difference, CN4 and N2 shear force interaction of 2 / c-CN6 structure ( Figure 6 ), the results show that the shearing effect between CN4 and N2 under high pressure is the key to the synthesis of this compound. The bonding characteristics analysis is mainly evaluated by calculating the crystal orbital Hamiltonian overlap layout function integral evaluation using LOBSTER software. The results show that strong covalent single bonds are the key to improving mass density and energy density. I 2 d The calculation results of charge localization function and charge difference of -CN4 under normal pressure showed that its stability was poor, so it was further eliminated and other structures with good stability were evaluated for performance.

[0034] 10. Performance evaluation. The mass density is obtained based on the ratio of the volume of the crystal structure to the relative atomic mass. The energy density is calculated by the energy difference of the decomposition reaction. The mechanical properties such as hardness and Poisson's ratio are calculated by the first-principle calculation software VASP. The detonation performance of the normal pressure stable structure is evaluated using the Kamlet-Jacobs (KJ) equation. C The 2-CN2 structure is eliminated.

[0035] 11. Obtain a mass density higher than 2.5g / cm 3 , new carbon-based nitrogen-rich energetic materials with energy density higher than 7.2 kJ / g, Figure 7 show, P 2 / c-CN6 is the binary stable nitrogen-rich energetic material with the highest known energy density.

Claims

1. A method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure, characterized in that: The following steps are involved: (1) Structural assembly of CN4 functional group units and N2 structural units; (2) Structural optimization under high pressure to retain the structure with the lowest energy under each component; (3) Calculation of formation energy to obtain the convex hull diagram under high pressure; (4) High-pressure stability evaluation to eliminate unstable structures and evaluate the high-pressure synthesis route for stable structures; (5) Obtaining the structural phase at normal pressure; (6) Physical property evaluation at normal pressure, eliminating structures with poor stability at normal pressure and conducting performance evaluation on structures with good stability; (7) Performance evaluation, eliminating structures with poor performance; (8) The structures with good performance obtained are the target carbon-based nitrogen-rich energetic materials.

2. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The specific steps of structural assembly are: using CN4 functional group units and N2 structural units for structural assembly, during the assembly process, the CN4 groups share the N atoms in CN4 to generate carbon-based nitrogen-rich random crystal structures of CN2, CN3, CN4, CN5, CN6, and CN7.

3. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The specific steps of performing structural optimization under high pressure and retaining the structure with the lowest energy under each component are as follows: optimizing the generated carbon-based nitrogen-rich random crystal structures of CN2, CN3, CN4, CN5, CN6, and CN7 by step-by-step optimization under pressures of 10 GPa, 20 GPa, 30 GPa, 40 GPa, 50 GPa, 60 GPa, 70 GPa, 80 GPa, 90 GPa, and 100 GPa; sorting the energies by reading the energy output by the structural optimization, and screening to obtain the structure with the lowest energy under each pressure point of 10 GPa, 20 GPa, 30 GPa, 40 GPa, 50 GPa, 60 GPa, 70 GPa, 80 GPa, 90 GPa, and 100 GPa for each component.

4. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The formation energy is calculated to obtain a convex hull diagram under high pressure: the formation energy of the most stable carbon-based nitrogen-rich structure at each pressure point is calculated by referring to the most stable structure of the reference phase at pressure points of 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa and 100GPa; the convex hull diagram of carbon-based nitrogen-rich energetic materials is constructed by the formation energy of the most stable carbon-based nitrogen-rich structure at pressure points of 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa and 100GPa; the stable structural phase with a distance from the solid line less than 0.1eV / atom in the convex hull diagram is screened and defined as a dominant carbon-based nitrogen-rich energetic material structural phase with the possibility of synthesis under high pressure.

5. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The specific steps of high-pressure stability evaluation are: analyzing the stability of the structure in the convex hull diagram through phonon spectrum, molecular dynamics, formation mechanism and charge transfer.

6. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The specific steps of the high-pressure synthesis route evaluation are: calculating the enthalpy difference diagram of the structural phases of the advantageous carbon-based nitrogen-rich energetic materials that have the possibility of synthesis under high pressure, and analyzing the potential synthesis reactants and synthesis pressure points.

7. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The specific steps to obtain a stable structural phase at normal pressure are: by releasing the pressure, using the first-principles software VASP to optimize at normal pressure to obtain an advantageous carbon-based nitrogen-rich energetic material structural phase that is possible to synthesize under high pressure.

8. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The specific steps of evaluating the physical properties at normal pressure are: calculating the charge localization function, charge difference, and group interaction of the normal pressure structural phase, and evaluating the structural bonding characteristics.

9. The method for designing the crystal structure of a carbon-based nitrogen-rich energetic material based on functional group assembly under high pressure according to claim 1, characterized in that: The specific steps of performance evaluation are: obtaining mass density, energy density, and calculating the detonation performance of the normal pressure stable structure.

10. The method for designing the crystal structure of carbon-based nitrogen-rich energetic materials based on functional group assembly under high pressure according to claim 1, characterized in that: Carbon-based nitrogen-rich energetic materials are P 2 / c-CN6.

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