A method for evaluating the stability of substances based on the decomposition of initial bonds in the molecular crystals of energetic compounds.

Abstract

This invention belongs to the field of computational chemistry of energetic materials, specifically relating to a method for evaluating the stability of substances based on the decomposition of initial bonds in the molecular crystal of energetic compounds. This method addresses the technical problems that the "bond energy method" is not applicable to molecular crystal models, and the "bond order method" cannot compare the stability of compounds laterally. By calculating the energy levels of chemical bonds within the molecular crystal of energetic compounds, this invention can both vertically compare the strength of all chemical bonds in the system to determine the initial bonds to decompose, and horizontally compare the energy levels of the initial bonds decomposed in different energetic compounds to determine the stability of the substances, thus overcoming the shortcomings of the existing "bond order method."

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of computational chemistry of energetic materials, and relates to the analysis of chemical bonds in the molecular crystal of an energetic compound, in particular to a method for determining the decomposition initiation bond of a molecular crystal of an energetic compound and a method for evaluating the stability of a substance. BACKGROUND

[0002] In recent years, high-energy density energetic materials have been the focus of international academic research. Domestic and foreign scholars have done a lot of research on balancing the energy and safety of energetic compounds. With the rapid development of quantum chemistry theory and computer science, the study of the relationship between molecular structure and energetic characteristics has become the main trend of energetic compound research, and computational chemistry research is an important theoretical basis in the molecular design stage.

[0003] The stability of an energetic compound is one of the important standards for measuring the safety of the production, use, transportation and storage process of an energetic compound. In the prior art, there are mainly two methods to study the stability of an energetic compound:

[0004] (1) "Bond energy method": the decomposition initiation bond of a molecule is determined by calculating the bond energy of the chemical bond in the molecule, and the stability of the compound is compared; the lower the bond energy, the easier the chemical bond breaks, and the bond with the lowest bond energy is the decomposition initiation bond of the molecule, and the lower the bond energy of the decomposition initiation bond of the molecule, the worse the stability of the substance.

[0005] (2) "Bond order method": the decomposition initiation bond of a molecule is determined by calculating the bond order of the chemical bond in the molecule; the lower the bond order, the more unstable the chemical bond, and the bond with the lowest bond order is the decomposition initiation bond.

[0006] However, the existing technical model has the following two technical defects:

[0007] (1) The calculation model of the "bond energy method" has limitations, and the "bond energy method" is usually only applicable to a single molecule model, but there are many types of energetic compounds, and a large number of energetic compounds containing metal ions have coordination polymer type molecular crystal structures, and cannot be separated into a single molecule structure, such as copper azide (Cu(N3)2), silver azide (AgN3) and the like;

[0008] (2) The "bond order method" can only vertically compare the bond order of the chemical bond of the molecule of the energetic compound to determine the decomposition initiation bond of the substance, and cannot horizontally compare the bond order of the decomposition initiation bond between different energetic compounds, and cannot determine the stability of the molecule of the energetic compound.

[0009] The two technical defects affect the reliability of the research results of the front-end design of the energetic compound, cause the blindness of the molecular design, increase the risk in the process of experimentally synthesizing the energetic compound, and limit the application development of the computational chemistry in the research of the structure-activity relationship of the energetic material. SUMMARY

[0010] In view of the defects in the prior art, the application provides a method for evaluating the stability of substances based on decomposition initiation bonds in a molecular crystal of an energetic compound, wherein the energy level of the decomposition initiation bond is used to represent the stability of the energetic compound molecule, and the method is used to evaluate the stability of a plurality of energetic compounds.

[0011] The method comprises the following steps:

[0012] In step one, the energy level of the decomposition initiation bond of each energetic compound molecule is obtained by using steps 1-4.

[0013] In step 1, the crystal structure data of the energetic compound molecular crystal is obtained, and the first-principle method is used to obtain the optimized molecular crystal structure data based on the predefined parameters, wherein if there is a lone electron in the structure of the energetic compound, spin polarization calculation is set in the optimization process, and if there is no lone electron in the structure of the energetic compound, non-spin polarization calculation is set in the optimization process.

[0014] The molecular crystal structure data comprises the cell length, the cell direction and the original fractional coordinates of all atoms in the molecular crystal; the predefined parameters comprise the plane wave cutoff energy, the number of Brillouin zone points, the electronic energy convergence standard and the atomic force convergence standard; and the optimized molecular crystal structure data comprises the optimized cell length, the optimized cell direction and the optimized fractional coordinates of all atoms in the molecular crystal.

[0015] In step 2, based on the optimized molecular crystal structure data, the number of Brillouin zone points is increased based on the number of Brillouin zone points in step 1, the symmetry of the Brillouin zone in the calculation process is cancelled, the PAW pseudo-potential is used, the total number of energy bands in the calculation is specified, the first-principle calculation method is used to perform single-point energy calculation on the energetic compound molecule to obtain the wave function file, if there is a lone electron in the structure of the energetic compound, spin polarization calculation is set in the single-point energy calculation, and if there is no lone electron in the structure of the energetic compound, non-spin polarization calculation is set in the single-point energy calculation.

[0016] Step 3, according to the wave function file obtained in step 2, and setting the range of electronic energy to be calculated, the integral value of the crystal orbital Hamiltonian population of each chemical bond in the molecular crystal of the energetic compound is calculated (IpCOHP value), if spin polarization calculation is set in the single-point energy calculation in step 2, there are two IpCOHP values for each chemical bond, if non-spin polarization calculation is set in the single-point energy calculation in step 2, there is only one IpCOHP value for each chemical bond; for the chemical bond with two IpCOHP values, the energy level of the chemical bond is the sum of the two IpCOHP values; for the chemical bond with one IpCOHP value, the IpCOHP value is the energy level of the chemical bond;

[0017] Step 4, comparing the levels of the energy levels of the chemical bonds in the energetic compound molecule, the higher the energy level, the more unstable the chemical bond, and the chemical bond with the highest energy level is the decomposition initiation bond of the energetic compound;

[0018] Step 2, comparing the decomposition initiation bonds in multiple molecular crystals of energetic compounds, the more stable the energetic compound with the higher energy level of the decomposition initiation bond.

[0019] In an optional scheme, the plane wave cutoff energy in the pre-defined parameters in step 1 is 650-850eV, the electronic energy convergence criterion is 1.0×10 -4 -1.0×10 -5 eV atom -1 , and the atomic force convergence criterion is The number of Brillouin zone points is L×M×N, and 40≤a×L=b×M=c×N≤70 or 40≤a×L≈b×M≈c×N≤70, a, b and c are the lengths of the initial molecular crystal cell of the energetic compound.

[0020] In an optional scheme, the number of Brillouin zone points added in step 2 is 2-3 times the number of Brillouin zone points in step 1.

[0021] In an optional scheme, the total number of energy bands in the specified calculation in step 2 is in the range of N elec / 2+N atom -N elec / 2+2×N atom , wherein N elec is the number of valence electrons in the molecular crystal of the energetic compound, and N atom is the number of atoms in the molecular crystal of the energetic compound.

[0022] In an optional scheme, the range of electronic energy to be calculated in step 3 is: the lowest electronic energy is in the range of -10 to -6eV, and the highest electronic energy is in the range of 6 to 10eV.

[0023] In an alternative scheme, the LOBSTER program is used to calculate the IpCOHP value of each chemical bond in the energetic compound molecular crystal.

[0024] Compared with the prior art, the method of the present application can be used for the crystal structure model of energetic compound molecular crystals, especially the crystal structure model of coordination polymers, and makes up for the shortcomings of the prior art "bond energy method";

[0025] In addition, the method of the present application can not only longitudinally compare the strengths of all chemical bonds in the system to determine the decomposition initiation bond, but also laterally compare the energy levels of the decomposition initiation bonds of different energetic compounds to determine the material stability of the energetic compounds, and makes up for the shortcomings of the prior art "bond order method". BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 (a) is a schematic diagram of the asymmetric unit structure of AgN3 in Example 1, (b) is a crystal orbital Hamiltonian population diagram and IpCOHP value of the N=N bond of the azide ion.

[0027] Figure 2 (a) is a schematic diagram of the asymmetric unit structure of Cu(N3)2 in Example 2, (b) is a crystal orbital Hamiltonian population diagram and IpCOHP value of the four chemical bonds.

[0028] Figure 3 (a) is a schematic diagram of the asymmetric unit structure of CuN3 in Example 3, (b) is a crystal orbital Hamiltonian population diagram and IpCOHP value of the four chemical bonds. DETAILED DESCRIPTION

[0029] Unless otherwise specified, the terms used herein are understood in accordance with the understanding of those of ordinary skill in the relevant art.

[0030] "Structure optimization" in the present application refers to: using computational chemistry software based on first-principles calculation to optimize the position coordinates of atoms in the molecular crystal and calculate the properties, selecting relevant functions and pseudo-potentials, and selecting a geometry optimization task, wherein the existing algorithm based on first-principles calculation is known to those skilled in the art.

[0031] For a specific energetic compound molecule or molecular crystal, there are multiple chemical bonds, and according to the bond length, the types of atoms forming the chemical bond, and the chemical environment in which the chemical bond is located, the multiple chemical bonds can be classified into multiple types, each type of chemical bond contains multiple chemical bonds, and the energy levels of different types of chemical bonds can be compared in step 4 of the present application.

[0032] The following provides specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention. The present invention will be further described in detail below with reference to the embodiments.

[0033] Example 1:

[0034] This embodiment uses the method of the present invention to obtain the decomposition initiation bond energy level of the energetic compound AgN3. The specific method includes the following:

[0035] Step 1: Obtain the crystal structure data of AgN3 crystal. According to the predefined parameters, optimize the AgN3 crystal structure data using the first-principles method. If there are no lone electrons in the AgN3 crystal structure, non-spin polarization calculation is set during the optimization process.

[0036] The molecular crystal structure data includes cell length, cell orientation, and original fractional coordinates of all atoms in the molecular crystal. The predefined parameters include plane wave cutoff energy, number of Brillouin zone points, electronic energy convergence criterion, and atomic force convergence criterion. The optimized molecular crystal structure data includes optimized cell length, optimized cell orientation, and optimized fractional coordinates of all atoms in the molecular crystal.

[0037] In this embodiment, the plane wave cutoff energy is 850 eV, and the electron energy convergence standard is 1.0 × 10⁻⁶. -4 eV atom -1 Atomic force convergence standard Using a Brillouin zone lattice of 5×5×5, the initial (i.e., before optimization) AgN3 crystal cell length

[0038] Step 2: Based on the optimized AgN3 crystal structure data and the predefined parameters in Step 1, increase the number of Brillouin zone lattice points, cancel the symmetry of the Brillouin zone during the calculation, use the PAW pseudopotential, specify the total number of energy bands in the calculation, and set non-spin polarization calculation in the single-point energy calculation if there are no lone electrons in the AgN3 crystal structure. Use the first-principles calculation method to calculate the single-point energy and obtain the wavefunction file.

[0039] In this embodiment, the number of Brillouin zone grid points is increased to 10×10×10, and a PAW pseudopotential is used, specifically N(2s 2 2p 3 ) and Ag(4d 10 5s 1 The total number of bands in the calculation is specified as 72.

[0040] Step 3, according to the wave function file obtained in Step 2, setting the electronic energy range to be calculated, running the LOBSTER program, and calculating the integral value (IpCOHP) of the crystal orbital Hamiltonian population of each chemical bond in the molecular crystal of the energetic compound, if spin polarization calculation is set in the single-point energy calculation in Step 2, there will be two IpCOHP values for each chemical bond, and if non-spin polarization calculation is set in the single-point energy calculation in Step 2, there will be only one IpCOHP value for each chemical bond;

[0041] The electronic energy range calculated in this embodiment is -10~6eV, and non-spin polarization calculation is set in the single-point energy calculation. According to the length of each chemical bond in the AgN3 crystal, the types of atoms forming the chemical bond, and the chemical environment in which the chemical bond is located, it is known that there are three types of chemical bonds in this structure, namely Ag--N bond and two types of N=N bond in azide ion (N3 - ). The COHP (crystal orbital Hamiltonian population) and IpCOHP values of the three types of chemical bonds are calculated, wherein the Ag--N bond is an ionic bond, indicating that there is no electron cloud overlap between Ag + and N3 - ; the COHP and IpCOHP values of the two types of N=N bond are the same, and the results are shown in Table 1. Figure 1

[0042] Step 4, comparing the levels of the chemical bond energy levels in the molecular crystal of the energetic compound, the higher the energy level, the more unstable the chemical bond, and the chemical bond with the highest energy level is the decomposition initiation bond of the energetic compound;

[0043] In this embodiment, the decomposition initiation bond in the AgN3 crystal is the N=N bond in the azide ion, and the energy level of the decomposition initiation bond is -19.18eV. The chemical bond energy levels are listed in Table 1.

[0044] Example 2:

[0045] In this embodiment, the method of the present application is used to obtain the decomposition initiation bond energy level of the energetic compound Cu(N3)2, and the specific method comprises the following steps:

[0046] In this embodiment, the Brillouin zone grid point number of the Cu(N3)2 crystal in Step 1 is 4x20x6; the cell length of the Cu(N3)2 crystal is 4.09x 4.09x 6.48 angstroms;

[0047] In this embodiment, the Brillouin zone grid point number of the Cu(N3)2 crystal in Step 2 is 8x40x12, and the PAW pseudo-potential used is N(2s 2 2p 3 ) and Cu(3d 10 4s 1 ), and the total number of energy bands in the designated calculation is 144;

[0048] ​In this embodiment, the electronic energy range calculated in step 3 is -10-10eV, and spin polarization calculation is set for the Cu(N3)2 crystal. There are four chemical bonds in the Cu(N3)2 crystal structure, which are Cu 2+ and N3 - coordination two Cu─N bonds and two N═N bonds in the azide ion. The COHP and IpCOHP values of the four chemical bonds are calculated, and the results are shown in Figure 2 ;

[0049] In this embodiment, the two IpCOHP values of each chemical bond of the Cu(N3)2 crystal in step 4 are added to obtain the energy level of the chemical bond, and the energy levels of the four chemical bonds are listed in Table 1. The Cu1─N1 bond is the decomposition initiating bond, and the energy level is -0.59eV.

[0050] Example 3

[0051] In this embodiment, the method of the present application is used to obtain the decomposition initiating bond energy level of the energetic compound CuN3, and the specific method comprises the following steps:

[0052] In this embodiment, the Brillouin zone grid number of step 1 is 9x9x5 for the CuN3 crystal; the cell length of the CuN3 crystal is a=0.637nm, b=0.637nm, and c=0.637nm.

[0053] In this embodiment, the Brillouin zone grid number of step 2 for the CuN3 crystal is 18x18x10, and the PAW pseudo-potential used is N(2s 2 2p 3 ) and Cu(3d 10 4s 1 ), and the total number of energy bands in the calculation is 168;

[0054] In this embodiment, the electronic energy range calculated in step 3 is -10-10eV, and spin polarization calculation is set for the Cu(N3)2 crystal. There are four chemical bonds in the Cu(N3)2 crystal structure, which are Cu + and N3 - coordination two Cu─N bonds and two N═N bonds in the azide ion. The COHP and IpCOHP values of the four chemical bonds are calculated, and the results are shown in Figure 3 ;

[0055] In this embodiment, the energy levels of the four chemical bonds of the CuN3 crystal in step 4 are listed in Table 1. The Cu1─N3 bond is the decomposition initiating bond, and the energy level is -1.59eV.

[0056] Table 1 Chemical bond energy levels of examples 1 to 3

[0057]

[0058] Further compare the stability of the energetic compounds shown in examples 1-3, from example 1 to example 3 can be known:

[0059] (A) AgN3 is an ionic crystal, Ag + and N3 - are ionic bonds, N3 - structure is symmetrical, the chemical environment of two N=N bonds is the same, the bond is the decomposition initiation bond of AgN3, and the energy level is -19.18eV;

[0060] (B) Cu(N3)2 is a coordination polymer molecular crystal, in the structure, Cu 2+ and N3 - coordination bond Cu1-N1 is the decomposition initiation bond of Cu(N3)2, and the energy level is -0.59eV, in addition, in the structure, N3 - structure is asymmetrical, the energy level of N2=N3 is -17.89eV, which is weaker than the covalent bond of N3 - in AgN3;

[0061] (C) CuN3 is also a coordination polymer molecular crystal, in the structure, Cu + and N3 - coordination bond Cu1-N3 is the decomposition initiation bond of CuN3, and the energy level is -1.59eV, in addition, in the structure, N3 - structure is also an asymmetrical structure, the energy level of N2=N3 is -17.82eV, which is equivalent to the covalent bond of N3 - in Cu(N3)2, and is weaker than the covalent bond of N3 - in AgN3;

[0062] (D) According to the energy level of the decomposition initiation bond of the substances in examples 1-3, it can be inferred that the stability rule of the substances is AgN3>CuN3>Cu(N3)2.

[0063] At the same time, the drop hammer method is used to test the impact sensitivity H 50 value of the three substances, which are AgN3(47.4cm), CuN3(16cm), and Cu(N3)2(9cm), respectively, from the impact sensitivity test, the stability rule of the three substances is AgN3>CuN3>Cu(N3)2. The above test results are consistent with the results of the theoretical method in the present application, which shows that the method for evaluating the stability of substances based on the decomposition initiation bond in the energetic compound molecular crystal in the present application is reliable.

[0064] From the above analysis, it can be seen that the method according to the application is based on the decomposition initiation bond in the energetic compound molecular crystal to evaluate the stability of the substance, the evaluation result is consistent with the actual test result of the stability of the energetic compound molecular crystal in the existing literature, and it is proved that the method according to the application for evaluating the stability of the substance based on the decomposition initiation bond in the energetic compound molecular crystal is reliable.

Claims

1. A method for evaluating stability of a substance based on a decomposition initiation bond in a molecular crystal of an energetic compound, characterized by, The energy level of the decomposition initiation bond is used to characterize the substance stability of the energetic compound molecule, and the method is used to evaluate the substance stability of a plurality of energetic compounds, and the method comprises the following steps: Step 1, obtaining the energy level of the decomposition initiation bond of each energetic compound molecule by steps 1-4: Step 1, obtaining the crystal structure data of the energetic compound molecule crystal, and optimizing the crystal structure data to obtain the optimized crystal structure data based on the predefined parameters by using the first principle method, if there is a lone electron in the structure of the energetic compound, spin polarization calculation is set in the optimization process, if there is no lone electron in the structure of the energetic compound, non-spin polarization calculation is set in the optimization process; The molecular crystal structure data includes the cell length, the cell direction and the original fractional coordinates of all atoms in the molecular crystal; the predefined parameters include the plane wave cutoff energy, the number of Brillouin zone points, the electronic energy convergence standard and the atomic force convergence standard; the optimized molecular crystal structure data includes the optimized cell length, the optimized cell direction and the optimized fractional coordinates of all atoms in the molecular crystal; Step 2, based on the optimized molecular crystal structure data, and based on the predefined parameters of step 1, the number of Brillouin zone points is increased based on the number of Brillouin zone points in step 1, the symmetry of the Brillouin zone in the calculation process is cancelled, the PAW pseudo-potential is used, the total number of energy bands in the calculation is specified, and the first principle calculation method is used to perform single-point energy calculation on the energetic compound molecule to obtain the wave function file, if there is a lone electron in the structure of the energetic compound, spin polarization calculation is set in the single-point energy calculation, if there is no lone electron in the structure of the energetic compound, non-spin polarization calculation is set in the single-point energy calculation; Step 3, according to the wave function file obtained in step 2, and setting the electronic energy range to be calculated, the IpCOHP value of each chemical bond in the energetic compound molecule crystal is calculated, if spin polarization calculation is set in step 2, there are two IpCOHP values for each chemical bond, if non-spin polarization calculation is set in step 2, there is only one IpCOHP value for each chemical bond; for the chemical bond with two IpCOHP values, the sum of the two IpCOHP values is the energy level of the chemical bond; for the chemical bond with one IpCOHP value, the IpCOHP value is the energy level of the chemical bond; Step 4, comparing the energy levels of each chemical bond in the energetic compound molecule, the higher the energy level, the more unstable the chemical bond, and the chemical bond with the highest energy level is the decomposition initiation bond of the energetic compound; Step 2, comparing the decomposition initiation bonds in the molecular crystals of a plurality of energetic compounds, the higher the energy level of the decomposition initiation bond, the worse the substance stability of the energetic compound.

2. The method for evaluating the stability of a substance based on the decomposition initiation bond in a molecular crystal of an energetic compound according to claim 1, characterized by, The plane wave cut-off energy in the predefined parameters in step 1 is 650-850 eV, the electron energy convergence criterion is 1.0 x 10 -4 -1.0 x 10 -5 eV atom -1 , the atomic force convergence criterion is The number of Brillouin zone points is L x M x N, and 40 <= a x L = b x M = c x N <= 70 or 40 <= a x L = b x M = c x N <= 70, a, b and c are all initial energetic compound molecular crystal cell lengths.

3. The method for evaluating the stability of a substance based on the decomposition initiation bond in a molecular crystal of an energetic compound according to Claim 1, wherein The number of Brillouin zone points increased in step 2 is 2-3 times the number of Brillouin zone points in step 1.

4. The method for evaluating the stability of a substance based on the decomposition initiation bond in a molecular crystal of an energetic compound according to Claim 1, wherein The total number of energy bands in the specified calculation of step 2 ranges from N elec / 2+N atom ~N elec / 2+2×N atom , wherein N elec is the number of valence electrons in the energetic compound molecular crystal, and N atom is the number of atoms in the energetic compound molecular crystal.

5. The method of claim 1, wherein the energetic compound is selected from the group consisting of hydrazine, hydrazine derivatives, azides, azide derivatives, and mixtures thereof. The set electronic energy range to be calculated in step 3 is: the lowest electronic energy value range is-10-6eV, and the highest electronic energy value range is 6-10eV.

6. The method of claim 1, wherein the energetic compound is selected from the group consisting of hydrazine, hydrazine derivatives, azides, azide derivatives, and mixtures thereof. The IpCOHP value of each chemical bond in the energetic compound molecule crystal is calculated by using the LOBSTER program.

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