Pentazole eutectic salt prediction method

Abstract

The invention discloses a method for predicting pentazole eutectic salt, and belongs to the technical field of ultrahigh-energy energetic materials. Eutectic host molecules and ligand molecules are designed based on weak interaction force in an energetic material system; the method comprises the following steps: generating a pentazole energetic eutectic initial structure by using USPEX software, carrying out optimization and property calculation on the generated structure by using an external interface program, then sequencing the optimized structure properties by using the USPEX software and generating a new structure according to the optimized structure properties, and repeating the steps until an optimal structure is generated. The USPEX and the external first principle program or molecular dynamics simulation software are completely open-source free programs, and the evolutionary algorithm has the excellent characteristics of high efficiency, reliability, diversity and the like, so that the calculation method provided by the invention can remarkably reduce the prediction cost of the ionic salt eutectic and improve the calculation precision and speed. The method provides a new strategy in the technical field of eutectic, and has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of eutectic technology, and particularly relates to a method for predicting eutectics. Background Art

[0002] In recent years, non-metal salts of pentazole (N 5 ˉ) have become a hot topic in the field of energetic materials due to their potential to exceed three times the TNT equivalent in terms of explosive energy. However, the reported non-metal salts of N 5 ˉ have problems such as low density, poor oxygen balance, and insufficient thermal stability. Therefore, the modification of non-metal salts of pentazole has become the focus of pentazole chemistry research. It has been found that the eutectic modification method shows good prospects in regulating key properties such as the energy performance, mechanical performance, and safety performance of energetic materials. In recent years, certain progress has been made in the synthesis of pentazole eutectic salts. However, up to now, only a few eutectic salts such as NH 4 + N 5 ˉ / H 2 O 2 、N 2 H 5 + N 5 ˉ / PDO, HTATOT + N 5 ˉ / TATOT, NH 4 + N 5 ˉ / NH 4 Cl, etc. have been synthesized and reported. The main reason is that the ion pairs of ionic eutectic salts will produce strong Coulomb repulsive forces, making it difficult to form eutectics. In addition, the eutectic method has problems such as a long screening period, high experimental costs, and harsh experimental conditions. Therefore, rational design of eutectics or virtual screening of eutectics through computational chemistry has gradually become a research hotspot. Currently, crystal structure prediction mainly relies on the Monte Carlo simulated annealing method in the Polymorph module of the commercial software Materials Studio. However, this method has problems such as slow calculation speed, poor universality, and low accuracy, and the software is expensive. In view of this, the present invention predicts the structure of pentazole eutectic salts based on the open-source and free evolutionary algorithm USPEX software package and first-principles programs (such as CP2K, Quantum Espresso, etc.) or molecular dynamics simulation software (such as LAMMPS, etc.), laying a solid theoretical foundation for the experimental synthesis of pentazole eutectic salts. Summary of the Invention

[0003] The present invention overcomes the deficiencies of the prior art and provides a method for predicting pentazole eutectic salts.

[0004] The technical solution for achieving the object of the present invention is as follows: The present invention designs a prediction method for pentazole cocrystal salts, and the specific operation steps are as follows: Based on any one or more weak intermolecular forces such as N-H···O / N-H···N / C-H···O / C-H···N hydrogen bonds, NO 2 -π (p-π) interactions, π-π stacking, etc., design the cocrystal structures of pentazole cocrystal salt hosts and ligands; Use software packages such as USPEX and CP2K or Quantum Espresso or LAMMPS to predict the structures of the above pentazole energetic cocrystals. The specific operation steps are as follows: (1) Based on the main ligand molecular formula, create a cation MOL_1 file, a pentazole anion MOL_2 file, and a ligand MOL_3 file; (2) Establish the INPUT input file of USPEX; (3) Establish the structure optimization relaxation files of USPEX (cp2k_options_1, cp2k_options_2, cp2k_options_3 or qEspresso_options_1, qEspresso_options_2, etc.), start USPEX at the server terminal, and perform calculations.

[0005] Preferably, the MOL files in step (1) are generated based on the Molden and Avogadro programs. The cations in step (1) include any one of small molecule ammonium cations (A), hydroxylamine cations (B), and hydrazine cations (C), chain-like aminoguanidine cations (D), diaminoguanidine cations (E), biguanide cations (F), monocyclic 4H-1,2,4-triazole-3,4,5-triamine (G), 4-(aminohydrazinomethyl)-1,2,5-oxadiazol-3-amine cations (H), and 1H-1,2,4-triazole-1-carboxamidine cations (I), bicyclic 5-(4-amino-2,3-dihydro-1,2,5-oxadiazol-3-yl)-4H-1,2,4-triazole-3,4-diamine cations (J), polycyclic 7H-[1,2,4]triazolo[4,3-b][1,2,4]triazole-3,6,7-triamine cations (K), and 5-(nitrosamino)hexahydroimidazo[4,5-d]imidazol-2(1H)-imine cations (L), etc.; The ligands include small molecule H 2 O 2(I), ammonium dinitramide (II), chain-like 1,1,1-trinitroethane (III), ethyl 2,2,2-trinitrocarbamate (IV), monocyclic 3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-amine (V), 3-dinitroazetidine (VI), pyrazine-1,4-dioxide PDO (VII), fused-ring 1,3,4,6-tetranitro-1,4-dihydropyrazolo[4,3-c]pyrazole (VIII), or any one of the like. Representative cationic structures and ligand structures are shown below:

[0006] Preferably, establishing the INPUT input file of USPEX in step (2) includes the following steps: (a) The task type of the input file INPUT of USPEX is calculationType = 310, and the optimization function optType is enthalpy; (b) Set the atom types atomType (elements such as C, H, O, N, etc.), molecular molar ratio numSpeices, atomic distance matrix IonDistances, minimum distance matrix Molcenters between molecular geometric centers, unit cell volume Latticevalues, and calculation method commandExecutable (i.e., external interface program); (c) During the calculation process, a certain number of structures are randomly generated according to the space group, and the maximum number of simulation generations of the population, the number of structures in each generation, and the proportion of individuals used to generate the next generation in each generation are set to achieve convergence; the generation method of the structure is mainly set based on the variational operator module, including genetic generation (fracGene), randomly generating structures from the space group (fracRand), lattice mutation (fracLatMut), soft mode mutation (racAtomsMut), generating by permutation operation (fracPerm), generating by orientation mutation (fracRotMut), generating by topological random machine (fracTopRand). When setting, it can be one or a combination of multiple types, but the sum of the proportion fractions of each variational operation is 1.

[0007] Preferably, the specified space groups include but are not limited to the following ten common space groups: P 2 1 / c (14), P -1 (2), P 2 1 2 1 2 1 (19), C 2 / c (15),P 2 1 (4), Pbca (61), Cc (9), P 1 (1), Pca 21 (29) and Pna 2 1 (33), where the numbers in parentheses represent the corresponding space group labels.

[0008] Preferably, during the convergence process, after multiple generations of the evolutionary algorithm, the simulation stops when the simulated structure no longer changes, that is, the converged unit cell structure obtained by simulation is the optimal structure.

[0009] The convergence condition is to sort the parent and offspring optimized unit cells by energy and retain the unit cell structures with the lowest energy at the front as the parent unit cell structures of the second generation. By analogy, the offspring unit cell structures of the third generation, fourth generation, etc. can be generated until any one of the optimal unit cells with the highest ranking in the offspring during consecutive multiple generations of the evolutionary process does not change compared to the parent, then it is the optimal structure.

[0010] Preferably, the files for structure relaxation in the Specific file are set. For example, the rough calculation of fixing the unit cell parameters and optimizing the atomic positions is achieved using cp2k_options_1, the structure relaxation is performed under a fixed external pressure based on general precision conditions using cp2k_options_2, and cp2k_options_3 is for high-precision geometric structure optimization.

[0011] Compared with the prior art, the obvious advantages of the present invention: (1) The present invention discloses a method for predicting pentazole eutectic salts, providing a new idea for the prediction of the structure and properties of ionic eutectics; (2) The present invention generates structures based on the evolutionary algorithm USPEX program and performs structure optimization and property calculation through external interface programs such as CP2K or Quantum Espresso or LAMMPS, improving the prediction speed and accuracy of pentazole eutectic salts, greatly reducing the calculation cost, and providing theoretical support for experimental synthesis.

[0012] Design co-crystal host molecules (pentazole non-metal salts) and ligand molecules based on the weak intermolecular forces in energetic material systems; generate the initial structure of pentazole energetic co-crystals using the USPEX software, optimize the generated structure and calculate its properties using an external interface program, and then the USPEX software sorts the properties of the optimized structure and generates new structures accordingly. This process is repeated until the optimal structure is obtained. Since both USPEX and the used external first-principles program or molecular dynamics simulation software are completely open-source and free programs, and the evolutionary algorithm has excellent characteristics such as high efficiency, reliability, and diversity, the calculation method provided by the present invention can significantly reduce the prediction cost of ionic salt co-crystals and improve the calculation accuracy and speed. This method provides a new strategy in the field of co-crystal technology and has good application prospects. Description of the Drawings

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the attached drawings introduce the present invention patent accordingly: Figure 1 It is the co-crystal diagram of pentazole hydroxylamine and hydrogen peroxide in Example 1.

[0014] Figure 2 It is the relationship diagram of the enthalpy of formation and volume in the prediction of the co-crystal of pentazole hydroxylamine and hydrogen peroxide in Example 1.

[0015] Figure 3 It is the relationship diagram of the number of structures and the enthalpy of formation in the prediction of the co-crystal of pentazole hydroxylamine and hydrogen peroxide in Example 1.

[0016] Figure 4 It is the co-crystal diagram of pentazole amine and 2,2,2-trinitroethyl carbamate in Example 2.

[0017] Figure 5 It is the flowchart of the operation of the prediction method of the present invention. Detailed Embodiments

[0018] The present invention will be further described below in conjunction with the embodiments.

[0019] Example 1 The prediction of the co-crystal of pentazole hydroxylamine and hydrogen peroxide is as follows: 1. Based on the main ligand molecular formula, create a hydroxylamine ion MOL_1 file, a pentazole anion MOL_2 file, and a hydrogen peroxide MOL_3 file 2. Establish the INPUT input file of USPEX, and the steps are as follows: (1) The task type of the input file INPUT of USPEX is calculationType = 310, and the optimization function optType is enthalpy; (2) Set the atom type atomType to elements H, O, and N, and the molecular molar ratio numSpeices, that is, the ratio of pentazole hydroxylamine to hydrogen peroxide is 1:1. Set the atomic distance matrices IonDistances of H to H, H to O, H to N, O to H, O to O, O to N, N to H, N to O, and N to N to be: 1.02 Å, 1.24 Å, 1.26 Å, 1.24 Å, 1.64 Å, 1.66 Å, 1.26 Å, 1.66 Å, 1.69 Å respectively; the minimum distance matrix Molcenters between the molecular geometric centers are all 4 Å; the unit cell volume Latticevalues is 700 Å 3 ; (3) The structure of each generation is 20. The number of structures randomly generated in the first generation in the specified space group is 50. 20 generations are simulated. The simulation stops when the structure does not change after 10 generations of simulation. The converged unit cell structure is obtained through 20 generations of evolutionary algorithm; (4) Based on the convergence condition in (3), it is characterized in that: the parent and offspring optimized unit cells are sorted by energy, and the first 30 unit cell structures with the lowest energy are reserved as the parent unit cell structures of the second generation. By analogy, the offspring unit cell structures of the third generation, fourth generation... can be generated until the first 6 - 7 optimal unit cells of the optimal structure of the offspring do not change compared with the parent in 10 consecutive generations of evolution, then the optimal structure is considered to be found; (5) Set the variational operator module, that is, the offspring inherit 60% of the structure (fracGene) of the previous generation, randomly generate 20% of the structure (fracRand) in the specified space group, 10% of the structure of each generation of population is obtained through soft mode mutation or exchange operation (racAtomsMut), 10% is generated through orientation mutation (fracRotMut), and the offspring do not generate structures through permutation operation (fracPerm) and lattice mutation (fracLatMut), that is, the sum of the transformation fractions is 1; (6) Based on the specified space group in step (2), it includes but is not limited to the following space groups: P 2 1 / c (14), P -1 (2), P 2 1 2 1 2 1 (19), C 2 / c (15), P 2 1 (4), Pbca (61), Cc (9), P 1 (1), Pca 21 (29) andPna 2 1 (33), where the number in the parentheses represents the corresponding space group label; 3. Create the structure optimization relaxation file cp2k_options_1 of USPEX to optimize the unit cell parameters and atomic positions. Start USPEX at the server terminal for calculation. The steps are as follows: (1) For the cp2k_options_1, it is characterized in that the task type is CELL_OPT, the semi-empirical GFN1-xTB method is adopted, the k-point is selected as 2×2×2, and the DFT-D3(BJ) method is used for dispersion correction; (4) For the structure motion setting, it is characterized in that the pressure condition is 1 atm, the maximum displacement is 1.0×10 -3 Bohr, the maximum force is 1.0×10 -4 Bohr, the root mean square displacement is 1.0×10 -4 Bohr, the root mean square force is 1.0×10 -3 Bohr, the maximum number of steps for geometric optimization is 500 steps, and the stress tensor STRESS_TENSOR is output at each step during the optimization process; (3) For the self-consistent field (SCF) calculation, it is characterized in that the method for the initial guess wave function is ATOMIC, EPS_DEFAUL is 1.0×10 -12 , and the convergence accuracy is 1.0×10 -6 , and the maximum number of iterations is 250; 4. Repeatedly optimize according to the above steps until the most stable structure is obtained. The prediction results of the eutectic of pentazole hydroxylamine and hydrogen peroxide are as Figure 1 shown. This substance belongs to the triclinic system, P space group 1(1); the unit cell parameters are a = 9.4940 Å, b = 7.7621 Å, c = 7.8411 Å, α = 74.5220°, β = 83.5840°, γ = 76.5330°, V = 540.81 Å 3 ; the crystal density at 0 K is 1.696 g·cm -3 .

[0020] Example 2 Prediction of the eutectic of pentazoleamine and 2,2,2-trinitroethyl carbamate is as follows: 1. Based on the main ligand molecular formula, create the ammonium root MOL_1 file, the pentazole anion MOL_2 file, and the 2,2,2-trinitroethyl carbamate MOL_3 file 2. Establish the input file INPUT of USPEX as follows: (1)The task type of the input file INPUT of USPEX is calculationType = 310, and the optimization function optType is enthalpy; (2)Set the atomic species atomType as elements such as C, H, O, N, etc., the molecular molar ratio numSpeices as 2:1, and set the atomic distance matrices IonDistances between C and C, C and H, C and O, C and N, H and C, H and H, H and O, H and N, O and C, O and H, O and O, O and N, N and C, N and H, N and O, N and N to be: 1.74 Å, 1.29 Å, 1.69 Å, 1.71 Å, 1.29 Å, 1.02 Å, 1.24 Å, 1.26 Å, 1.69 Å, 1.24 Å, 1.64 Å, 1.66 Å, 1.71 Å, 1.26 Å, 1.66 Å, 1.69 Å respectively; the minimum distance matrix Molcenters between the molecular geometric centers is 4 Å; the unit cell volume Latticevalues is 800 Å 3 ; (3)The number of structures in each generation is 50, the number of structures randomly generated in the first generation in the specified space group is 50, 60 generations are simulated, and the simulation stops when the structures do not change after 10 generations of simulation. The converged unit cell structure is obtained through the evolutionary algorithm after 25 generations; (4)Based on the convergence condition in (3), it is characterized in that: the parent and offspring optimized unit cells are sorted by energy and the first 30 unit cell structures with the lowest energy are retained as the parent unit cell structures of the second generation. By analogy, the offspring unit cell structures of the third generation, the fourth generation... can be generated until in 10 consecutive generations of the evolutionary process, the first 6 - 7 optimal unit cells of the optimal structure of the offspring do not change compared with the parent, then the optimal structure is considered to be found (5)Set the variational operator module, that is, the offspring inherit 50% of the structure (fracGene) of the previous generation, 20% of the structures (fracRand) are randomly generated in the specified space group, 20% of the structures in each generation of the population are obtained through soft mode mutation or exchange operations (racAtomsMut), 10% of the structures are generated through orientation mutation (fracRotMut), and the offspring do not generate structures through permutation operations (fracPerm) and lattice mutation (fracLatMut), that is, the sum of the transformation fractions is 1; (6)Based on the specified space group in step (2), it includes but is not limited to the following space groups: P 2 1 / c (14)、 P -1 (2)、 P 21 2 1 2 1 (19), C 2 / c (15), P 2 1 (4), Pbca (61), Cc (9), P 1 (1), Pca 21 (29) and Pna 2 1 (33), where the numbers in parentheses represent the corresponding space group labels; 3. Establish the structure optimization relaxation file of USPEX. cp2k_options_1 realizes the optimization of fixed unit cell parameters and atomic positions. Use cp2k_options_2 to perform structure relaxation under fixed external pressure based on general precision conditions. cp2k_options_3 is for high-precision geometric structure optimization. Start USPEX on the server terminal and perform the calculations as follows: (1) The cp2k_options_1 is a geometric optimization file with the task type of GEO_OPT. It uses the PBE functional and the DZVP-MOLOPT-SR-GTH basis set. The integration grid is 4, the plane wave cut-off energy is 400 Ry, the reference cut-off energy is 45 Ry. In the self-consistent field (SCF), EPS_DEFAUL is 1.0×10 -10 , the convergence precision is 1.0×10 -5 , the maximum number of iterations is 250. In its grid settings, the old and new density matrices are mixed with a mixing factor of 0.4 to accelerate the convergence rate of the stable self-consistent field (SCF) calculation; the maximum displacement is 1.0×10 -4 Bohr, the maximum force is 1.0×10 -3 Bohr, the root mean square displacement is 1.0×10 -4 Bohr, the root mean square force is 1.0×10 -3 Bohr, and the maximum step of geometric optimization is 500 steps; (2) The cp2k_options_2 is a variable cell optimization file with the task type of CELL_OPT. Its pressure condition is 1 atm; the k-point is set to 2×2×2, the integration grid is 4, the plane wave cut-off energy is 500 Ry, the reference cut-off energy is 50 Ry. The SCF setting EPS_DEFAUL is 1.0×10 -12 , the convergence precision is 1.0×10 -6 , the maximum number of iterations is 250. In its grid settings, the old and new density matrices are mixed with a mixing factor of 0.4; the maximum displacement is 3.0×10 -3 Bohr, the maximum force is 4.5×10 -4For Bohr, the root-mean-square displacement is 1.5×10 -3 For Bohr, the root-mean-square force is 3.0×10 -4 For Bohr, the maximum number of steps for geometric optimization is 500 steps; (3)For the high-precision geometric optimization of cp2k_options_3, the task type is GEO_OPT. For each element, the GTH-NLCC-PBE pseudopotential and DZVP-MOLOPT-SR-GTH basis set are used. The dispersion correction is performed by the DFT-D3(BJ) method. The integration grid is 5, the plane-wave cutoff energy is 600 Ry, the reference cutoff energy is 60 Ry, and EPS_DEFAUL is 1.0×10 -14 , and the convergence accuracy is 1.0×10 -8 ; the maximum displacement is 3.0×10 -3 For Bohr, the maximum force is 1.0×10 -5 For Bohr, the root-mean-square displacement is 1.5×10 - 3 For Bohr, the root-mean-square force is 3.0×10 -4 For Bohr.

[0021] 4. Repeatedly optimize according to the above steps until the most stable structure is obtained. The prediction results of the eutectic of pentazoleamine and 2,2,2-trinitroethyl carbamate are as follows Figure 4 , and this substance belongs to the triclinic system, P space group 1(1); the unit cell parameters are a a = 15.3832 Å, b b = 7.2070 Å, c c = 7.3278 Å, α α = 87.9200°, β β = 91.4430°, γ γ = 87.5070°, V V = 810.82 Å 3 ; the crystal density at 0 K is 1.639 g·cm -3 .

[0022] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for predicting a pentazole eutectic salt, using USPEX and CP2K, Quantum Espresso or LAMMPS software packages to predict the structure of a designed pentazole eutectic salt, characterized in that: The steps include: (1) Based on the main ligand molecular formula, create the cation MOL_1 file, the pentazole anion MOL_2 file, and the ligand MOL_3 file; (2) Create the INPUT file for USPEX; (3) Establish the USPEX structure optimization relaxation file, start USPEX on the server terminal, perform calculations, and predict the structural formula of the pentazole eutectic salt.

2. The method for predicting pentazole eutectic salt according to claim 1, characterized in that: The MOL file in step (1) is generated based on the Molden and Avogadro program.

3. The method for predicting pentazole eutectic salt according to claim 1, characterized in that: The cations described in step (1) include small molecular ammonium cations (A), hydroxylamine cations (B) and hydrazine cations (C), chain aminoguanidine cations (D), diaminoguanidine cations (E), biguanidine cations (F), monocyclic 4H-1,2,4-thiazole-3,4,5-triamine (G), 4-(aminohydrazinemethyl)-1,2,5-oxadiazole-3-amine cations (H) and 1H-1,2,4-triazole-1-carboxamidinium cations ( I), any one of a linked 5-(4-amino-2,3-dihydro-1,2,5-oxadiazol-3-yl)-4H-1,2,4-triazole-3,4-diaminium cation (J), a fused-ring 7H-[1,2,4]triazolo[4,3-b][1,2,4]triazole-3,6,7-triamine cation (K) and a 5-(nitroimino)hexahydroimidazo[4,5-d]imidazol-2(1H)-iminium cation (L); The ligands include any one of small molecule H2O2 (I), ammonium dinitramide (II), chain 1,1,1-trinitroethane (III), 2,2,2-trinitroethyl carbamate (IV), monocyclic 3-nitro-1-(trinitromethyl)-1H-1,2,4-triazole-5-amine (V), 3-dinitroazetidine (VI), pyrazine-1,4-dioxide PDO (VII), and fused ring 1,3,4,6-tetranitro-1,4-dihydropyrazolo[4,3-c]pyrazole (VIII).

4. The method for predicting pentazole eutectic salt according to claim 1, characterized in that: The steps to create the USPEX INPUT file in step (2) include the following: (a) The task type of the USPEX input file INPUT is calculationType=310, and the optimization function optType is enthalpy; (b) Set the atomic type atomType to C, H, O, N elements, the molecular molar ratio numSpeices, the atomic distance matrix IonDistances, the minimum distance matrix between molecular geometric centers Molcenters, and the unit cell volume Latticevalues; (c) During the calculation process, a certain number of structures are randomly generated according to the space group, and the maximum simulation generation of the population, the number of structures in each generation, and the proportion of individuals in each generation used to generate the next generation are set to achieve convergence; the structure generation method is mainly based on the variational operator module, including genetic generation (fracGene), random generation of structure from space group (fracRand), lattice mutation (fracLatMut), soft mode mutation (racAtomsMut), permutation operation generation (fracPerm), orientation mutation generation (fracRotMut), topological randomizer generation (fracTopRand) One or more combinations, but the sum of the proportions of each variational operation is 1.

5. The method for predicting pentazole eutectic salt according to claim 4, characterized in that: The space groups in step (c) include P twenty one / c (14) P -1 (2), P 212121 (19), C 2 / c (15) P 21(4) Pbca (61) Cc (9) P 1 (1), Pca 21(29) and Pn 21 (33), the numbers in brackets represent the corresponding space group numbers.

6. The method for predicting pentazole eutectic salt according to claim 4, characterized in that: During the convergence process, after multiple generations of evolutionary algorithms, the simulation stops when the structure no longer changes, that is, the converged unit cell structure obtained by simulation is the optimal structure.

7. The method for predicting pentazole eutectic salt according to claim 6, characterized in that: The convergence condition is to sort the parent and child optimized unit cells by energy and retain the unit cell structure with the lowest energy at the front as the parent unit cell structure of the second generation. By analogy, the unit cell structures of the third, fourth, etc. generations of children can be generated until any optimal unit cell in the optimal structure with the front sequence number in the child generation does not change with the parent generation during multiple generations of evolution, which is the optimal structure.

8. The method for predicting pentazole eutectic salt according to claim 1, characterized in that: The relaxation file is selected from any one or more combinations of cp2k_options_1, cp2k_options_2, cp2k_options_3 or qEspresso_options_1, qEspresso_options_2.

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