Molecular dynamics simulation method for constructing amorphous model through precursor hydrolysis-pyrolysis

Abstract

The invention relates to a molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis, which utilizes the characteristic that main products in the precursor hydrolysis and pyrolysis process are respectively water, hydrogen and methane, selects reasonable criteria through a written Python script program, judges the bonding distance between atoms and identifies the generated products, and finally establishes a molecular dynamics model. And batch and circulating molecular dynamics simulation is realized, and the amorphous SiOC atomic model is obtained. According to the method, the combination of automation, batch and open source molecular dynamics calculation software LAMMPS is finally realized, the influence of human subjective factors is eliminated, the calculation efficiency is improved, the time cost of scientific researchers is saved, and careless mistakes caused by a large amount of operations are avoided. Besides, sol micromolecules can form a good network skeleton structure after being hydrolyzed and cured, the escape speed of gas products is slowed down, an amorphous SiOC model with higher free carbon content can be constructed, and the amorphous-nanocrystalline interface density of the material is improved.

Description

Technical Field

[0001] The present invention belongs to the field of amorphous ceramic material simulation, and relates to a molecular dynamics simulation method for constructing an amorphous model by hydrolysis-pyrolysis of a precursor, and specifically to a method for automatic and batch-linked open source molecular dynamics simulation based on molecular dynamics simulation. Background Art

[0002] Amorphous SiOC is isotropic at the macroscopic scale, but inhomogeneous at the micro-nanoscale. Its structure mainly includes amorphous SiO2 structure, free carbon, and mixed silicon tetrahedral structural units at the interface between the two. The type of functional groups contained in the precursor has a significant effect on the composition and structure of the hydrolysis and pyrolysis products. For example, the Si-H and Si-CH3 groups in PMHS can reduce the free carbon content in the product. It can be seen that the process of preparing ceramics by precursor pyrolysis is very complicated. It is difficult to fully understand the specific relationship between the component, structure and properties of SiOC and the precursor structure and preparation process by experimental means alone. Therefore, computer simulation can make up for the disadvantage of difficult high-temperature characterization. Appropriate simulation methods can be used to in situ and quantitatively study the influence of the process of preparing ceramics by precursor pyrolysis on the component, structure and properties of SiOC.

[0003] In summary, it is crucial to clarify the influence of precursors and hydrolysis-pyrolysis processes on the microstructure and comprehensive properties of amorphous SiOC. Nowadays, researchers usually use the melt annealing method to construct an amorphous model, that is, the system temperature is raised to a high temperature to form a "liquid phase" in the system, and then the system is relaxed at a high temperature to stabilize the energy and "liquid phase" structure of the system, and then the system is annealed to room temperature to finally obtain an amorphous structure. The annealing process can be handled in different ways. One is rapid annealing to keep the structure in a metastable amorphous structure; the other is multi-step annealing to fully relax the structure. However, the melt annealing method can only obtain the influence of element ratio and structure on material properties, and cannot clearly reveal the influence of precursor raw materials and hydrolysis-pyrolysis processes on the microstructure and comprehensive properties of materials. Summary of the invention

[0004] In order to reveal the influence of precursor raw materials and hydrolysis-pyrolysis process on the microstructure and comprehensive performance of amorphous materials, the purpose of the present invention is to utilize the characteristics that the main products of precursor hydrolysis and pyrolysis are water, hydrogen and methane respectively, and through the written Python script program, select reasonable criteria to judge the bonding distance between atoms, identify the generated products, realize batch and cyclic molecular dynamics simulation, and obtain the amorphous SiOC atomic model. The present invention finally realizes the automatic and batch combination with the open source molecular dynamics calculation software LAMMPS, eliminates the influence of human subjective factors, improves the calculation efficiency, saves the time cost of scientific researchers, and avoids the omissions caused by a large number of operations.

[0005] In order to achieve the above object, the present invention provides the following technical solution to achieve the above object: a molecular dynamics simulation method for constructing an amorphous model by hydrolysis-pyrolysis of a precursor, comprising the following steps:

[0006] 1) Constructing the precursor atomic model by melt annealing method;

[0007] 2) heating the obtained precursor atomic model to the hydrolysis temperature for relaxation to obtain the precursor atomic model under the hydrolysis condition;

[0008] 3) Performing hydrolysis simulation on the precursor atomic model to obtain the atomic structure model after hydrolysis;

[0009] 4) subjecting the atomic structure model after hydrolysis obtained in step 3) to molecular dynamics annealing simulation, and setting a relaxation time at a constant temperature and constant pressure to obtain a balanced precursor solidified atomic model;

[0010] 5) Perform high-temperature pyrolysis calculation on the precursor solidification atomic model to obtain the atomic structure model after pyrolysis;

[0011] 6) The atomic structure model after pyrolysis obtained in step 5) is subjected to molecular dynamics annealing simulation, and is relaxed for a set time at a constant temperature and constant pressure to obtain a fully balanced hydrolysis-pyrolysis amorphous SiOC atomic model.

[0012] The hydrolysis simulation of the precursor atomic model to obtain the atomic structure model after hydrolysis comprises the following steps:

[0013] ① Read the precursor atomic model, perform molecular dynamics simulation on it at the hydrolysis temperature for a set time, make the sol molecules undergo hydrolysis reaction, and output the molecular dynamics simulation trajectory file;

[0014] ② Read the last frame structure of the molecular dynamics simulation trajectory file as the hydrolysis intermediate structure, identify the generated water molecule hydrolysis products through the bonding criterion of oxygen-hydrogen atoms, and record the atomic numbers of the water molecules;

[0015] ③ Delete the water molecule products of the intermediate structure of hydrolysis, re-arrange the atomic numbers in sequence, and generate a new structure file, which is passed as the precursor atomic model to step ① for molecular dynamics hydrolysis simulation; if no new water molecules are generated, it indicates that the hydrolysis reaction is complete, and the latest structure file is used as the atomic structure model after hydrolysis.

[0016] The water molecule hydrolysis products generated by the oxygen-hydrogen atom bonding criterion are identified under the following identification conditions:

[0017] The bond lengths of oxygen-silicon, oxygen-carbon, and oxygen-oxygen are respectively greater than

[0018] The coordination number of the oxygen-hydrogen bond must be equal to 2.

[0019] In step 5), the high temperature pyrolysis calculation is performed on the precursor solidified atomic model to obtain the atomic structure model after pyrolysis, which includes the following steps:

[0020] 5.1) Reading the precursor solidification atomic model, performing molecular dynamics simulation on it at the pyrolysis temperature for a set time, causing the precursor solidification atomic model to undergo pyrolysis reaction, and outputting a molecular dynamics simulation trajectory file;

[0021] 5.2) reading the last frame structure of the molecular dynamics simulation trajectory file of step 5.1) as the pyrolysis intermediate structure; identifying the generated hydrogen pyrolysis products by hydrogen-hydrogen bonding criterion, and recording the atomic numbers constituting the hydrogen products; identifying the generated methane pyrolysis products by carbon-hydrogen bonding criterion, and recording the atomic numbers constituting the methane pyrolysis products;

[0022] 5.3) Delete the hydrogen pyrolysis products and methane pyrolysis products of the pyrolysis intermediate structure, generate a new structure file, and pass it to the molecular dynamics pyrolysis simulation in step 5.1) as the precursor solidification atomic model; when the methyl and hydrogen functional groups of the side chains of the sol molecules are completely removed, use the latest structure file as the atomic structure model after pyrolysis.

[0023] The generated hydrogen pyrolysis products are identified by the hydrogen-hydrogen bonding criterion, and the generated methane pyrolysis products are identified by the carbon-hydrogen bonding criterion. The identification conditions are as follows:

[0024] Hydrogen pyrolysis products: hydrogen-silicon, hydrogen-carbon, hydrogen-oxygen bond lengths are greater than Methane pyrolysis products: When carbon atoms form bonds with surrounding atoms, the shortest carbon-carbon, carbon-silicon, and carbon-oxygen bond lengths must be greater than And the coordination number of the carbon-hydrogen bond must be equal to 4.

[0025] The precursor atomic model is constructed by selecting an NPT ensemble relaxation of no less than 100 ps under the conditions of 300K and 0.1 MPa.

[0026] The hydrolysis simulation conditions are 400K, 0.1MPa, and NPT ensemble relaxation is selected for no less than 100ps; the hydrolysis simulation cycle is 400K, 0.1MPa, NPT ensemble, the number of hydrolysis cycle simulations is 1000 times, and each calculation is 2ps.

[0027] The atomic structure model after hydrolysis obtained in step 3) is subjected to molecular dynamics annealing simulation, the annealing rate from 400K to 300K is 0.1K / fs, and the NPT ensemble relaxation is selected at 300K and 0.1MPa for not less than 100ps; the high-temperature pyrolysis cycle is 1800K, 0.6GPa, NPT ensemble, and each pyrolysis cycle simulation calculation is 2ps.

[0028] The atomic structure model after pyrolysis obtained in step 5) is subjected to molecular dynamics annealing simulation, heated to 3000K and relaxed for 500ps, and annealed to room temperature and pressure at a rate of 0.1K / fs, and finally relaxed for 100ps using the NPT ensemble.

[0029] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the molecular dynamics simulation method of constructing an amorphous model by precursor hydrolysis-pyrolysis is implemented.

[0030] The present invention has the following beneficial effects and advantages:

[0031] 1. Taking advantage of the fact that the main products of the hydrolysis and pyrolysis processes of the precursor are water, hydrogen and methane respectively, a Python script program was written to select reasonable criteria to judge the bonding distance between atoms, identify the products generated by hydrolysis and pyrolysis, realize batch and cyclic molecular dynamics simulation, and obtain the hydrolysis-pyrolysis amorphous SiOC atomic model.

[0032] 2. Realize the automatic and batch use of molecular dynamics calculation software, eliminate the influence of human subjective factors, improve calculation efficiency, save the time cost of scientific researchers, and avoid omissions caused by a large number of operations.

[0033] 3. The use of the NPT ensemble during simulation can adjust the system density in real time according to the types and quantities of discharged hydrolysis and pyrolysis products, thus avoiding the errors caused by the inability of the NVT ensemble to control the system volume.

[0034] 4. The atomic model of amorphous SiOC obtained by this method shows the characteristics of amorphous SiOC prepared by precursor hydrolysis-pyrolysis method in the experiment. A large amount of free carbon network structure is generated in the amorphous matrix due to the cross-linking of the precursor skeleton and the decomposition of methane gas.

[0035] 5. In the present invention, the sol small molecules can form a good network skeleton structure after hydrolysis and solidification, slowing down the escape velocity of gas products, constructing an amorphous SiOC model with a higher free carbon content, and improving the amorphous-nanocrystalline interface density of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1Schematic diagram of the process of constructing an amorphous atomic model using the precursor hydrolysis-pyrolysis method based on molecular dynamics simulation;

[0037] Figure 2 MTMS and DMDMS molecular structures and simplified MTMS' and DMDMS' molecular structures;

[0038] Figure 3 From left to right are the initial structure, the solidified sample and the amorphous SiOC atomic structure model. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0040] The present invention discloses a method for constructing an amorphous atomic model by using a precursor hydrolysis-pyrolysis method based on molecular dynamics simulation, and belongs to the field of amorphous ceramic material simulation. The present invention utilizes the characteristics that the main products of the precursor hydrolysis and pyrolysis process are water, hydrogen and methane, respectively. Through the written Python script program, a reasonable criterion is selected to judge the bonding distance between atoms, identify the generated products, realize batch and cyclic molecular dynamics simulation, and obtain an amorphous SiOC atomic model. The present invention finally realizes the automatic and batch combination with the open source molecular dynamics calculation software LAMMPS, eliminates the influence of human subjective factors, improves the calculation efficiency, saves the time cost of scientific researchers, and avoids the omissions caused by a large number of operations. In addition, the sol small molecules can form a good network skeleton structure after hydrolysis and solidification, slow down the escape velocity of gas products, and can construct an amorphous SiOC model with a higher free carbon content, thereby improving the amorphous-nanocrystalline interface density of the material.

[0041] The present invention comprises the following steps:

[0042] 1) With the help of the open source molecular dynamics simulation software LAMMPS, a sol small molecule model with a certain molar ratio is constructed by melt annealing method, and the constructed structural model is fully relaxed at room temperature and pressure to achieve complete equilibrium in structure, energy and density, thereby obtaining a stable precursor atomic model;

[0043] 2) heating the obtained precursor atomic model to the hydrolysis temperature and performing sufficient relaxation for a certain period of time to obtain the precursor atomic model under the hydrolysis condition;

[0044] 3) Perform hydrolysis simulation on the precursor atomic model obtained in the previous step. When performing the hydrolysis simulation, the Python script program of the present invention needs to be executed to achieve the combination with the open source molecular dynamics simulation software LAMMPS:

[0045] ① Read the precursor atomic model, perform molecular dynamics simulation on it at the hydrolysis temperature for a certain period of time, make the sol molecules undergo hydrolysis reaction, and output the molecular dynamics simulation trajectory file;

[0046] ② Using the Python script program of the present invention to read the last frame structure of the previous trajectory file as the hydrolysis intermediate structure, identify the generated water molecule hydrolysis products through the bonding criterion of oxygen and hydrogen atoms, and record the atomic numbers constituting the water molecules;

[0047] ③ Deleting the water molecule products of the intermediate structure of the hydrolysis with the help of the Python script program of the present invention, and generating a new structure file to be passed to the molecular dynamics hydrolysis simulation in step ①; if steps ①-③ are cycled a certain number of times and no new water molecules are generated, it indicates that the hydrolysis reaction is complete, and the latest structure file is used as the atomic structure model after hydrolysis;

[0048] 4) subjecting the atomic structure model after hydrolysis obtained in step 3) to molecular dynamics annealing simulation, and relaxing it at constant temperature and pressure for a certain period of time to obtain a fully balanced precursor solidified atomic model;

[0049] 5) Perform high-temperature pyrolysis calculation on the precursor solidification atomic model obtained in the previous step. When performing high-temperature simulation, the Python script program of the present invention needs to be executed to achieve the combination with the open source molecular dynamics simulation software LAMMPS:

[0050] ① Read the solidified atomic model, perform molecular dynamics simulation on it at the pyrolysis temperature for a certain period of time, make the solidified atomic model undergo pyrolysis reaction, and output the molecular dynamics simulation trajectory file;

[0051] ② Using the Python script program of the present invention to read the last frame structure of the previous trajectory file as the pyrolysis intermediate structure, identify the generated hydrogen pyrolysis products by the hydrogen-hydrogen bonding criterion, and record the atomic numbers of the hydrogen products; identify the generated methane pyrolysis products by the carbon-hydrogen bonding criterion, and record the atomic numbers of the methane pyrolysis products;

[0052] ③ Using the Python script of the present invention, the hydrogen and methane molecular products of the intermediate structure of the pyrolysis are deleted, and a new structure file is generated and transferred to the molecular dynamics pyrolysis simulation in step ①; the pyrolysis process continuously cycles through steps ①-③ until the methyl and hydrogen functional groups of the side chains of the sol molecules are completely removed, and the latest structure file is used as the atomic structure model after pyrolysis;

[0053] 6) The atomic structure model after pyrolysis obtained in step 5) is subjected to molecular dynamics annealing simulation, and is relaxed for a certain period of time at a constant temperature and pressure to obtain a fully balanced hydrolysis-pyrolysis amorphous SiOC atomic model;

[0054] Preferably, in step 1), the system uses NPT ensemble relaxation of not less than 100 ps at 300K and 0.1 MPa;

[0055] Preferably, in step 2), the hydrolysis simulation condition is set to 400K, and the NPT ensemble relaxation is selected to be not less than 100ps under 0.1MPa conditions;

[0056] Preferably, in step 3), the hydrolysis cycle simulation method is set to 400K, 0.1MPa, NPT ensemble, the number of hydrolysis cycle simulations is 1000 times, and each calculation is 2ps; the criterion for judging the generation of water molecules in the hydrolysis product must meet the following conditions:

[0057] ① The bond lengths of oxygen-silicon, oxygen-carbon, and oxygen-oxygen are respectively greater than

[0058] ②The coordination number of the oxygen-hydrogen bond must be equal to 2;

[0059] Preferably, in step 4), the annealing rate from 400K to 300K is 0.1K / fs, and the NPT ensemble relaxation is selected to be not less than 100ps under the conditions of 300K and 0.1MPa;

[0060] Preferably, in step 5), the pyrolysis cycle simulation method is set to 1800K, 0.6GPa, NPT ensemble, and each pyrolysis cycle simulation calculation is 2ps; the criterion for judging the generation of hydrogen and methane molecules as pyrolysis products is:

[0061] ① Hydrogen pyrolysis products: hydrogen-silicon, hydrogen-carbon, hydrogen-oxygen bond lengths are greater than

[0062] ②Methane pyrolysis products: When carbon atoms form bonds with surrounding atoms, the shortest carbon-carbon, carbon-silicon, and carbon-oxygen bond lengths must be greater than And the coordination number of the carbon-hydrogen bond must be equal to 4;

[0063] Preferably, in step 6), the pyrolyzed atomic structure model is heated to 3000K and relaxed for 500ps, and annealed to room temperature and pressure at a rate of 0.1K / fs, and finally relaxed for 100ps using the NPT ensemble.

[0064] See also Figure 1 , combined with the calculation flow chart of constructing an amorphous atomic model by the hydrolysis-pyrolysis method, the implementation method of the present invention for constructing an amorphous atomic model by the precursor hydrolysis-pyrolysis method based on molecular dynamics simulation is explained, comprising the following steps:

[0065] 1) With the help of the open source molecular dynamics simulation software LAMMPS, a sol small molecule model with a certain molar ratio was constructed by melt annealing method, and the constructed structural model was fully relaxed for no less than 100ps using the NPT ensemble under 300K and 0.1MPa conditions to achieve complete equilibrium in structure, energy and density, thereby obtaining a stable precursor atomic model;

[0066] 2) The obtained precursor atomic model is heated to the hydrolysis temperature of 400K, and the NPT ensemble relaxation is selected at 0.1MPa for not less than 100ps to obtain the precursor atomic model under the hydrolysis condition;

[0067] 3) Perform hydrolysis simulation on the precursor atomic model obtained in the previous step. When performing the hydrolysis simulation, the Python script program of the present invention needs to be executed to achieve the combination with the open source molecular dynamics simulation software LAMMPS:

[0068] ① Read the precursor atomic model, perform 2ps molecular dynamics simulation on it using NPT ensemble under 400K, 0.1MPa hydrolysis conditions, make the sol molecules undergo hydrolysis reaction, and output the molecular dynamics simulation trajectory file;

[0069] ② The Python script of the present invention is used to read the last frame structure of the previous trajectory file as the hydrolysis intermediate structure, identify the generated water molecule hydrolysis products through the bonding criterion of oxygen and hydrogen atoms, and record the atomic numbers of the water molecules; the criterion for judging the generation of water molecules in the hydrolysis product must simultaneously meet the following conditions: the oxygen-silicon, oxygen-carbon, and oxygen-oxygen bond lengths are respectively greater than The coordination number of the oxygen-hydrogen bond must be equal to 2;

[0070] ③ Deleting the water molecule products of the intermediate structure of the hydrolysis with the help of the Python script program of the present invention, and generating a new structure file to be passed to the molecular dynamics hydrolysis simulation in step ①; if steps ①-③ are cycled a certain number of times and no new water molecules are generated, it indicates that the hydrolysis reaction is complete, and the latest structure file is used as the atomic structure model after hydrolysis;

[0071] 4) The atomic structure model after hydrolysis obtained in step 3) is subjected to molecular dynamics annealing simulation at a rate of 0.1 K / fs, and the NPT ensemble relaxation is selected at 300 K and 0.1 MPa for not less than 100 ps to obtain a fully balanced precursor solidification atomic model;

[0072] 5) Perform high-temperature pyrolysis calculation on the precursor solidification atomic model obtained in the previous step. When performing high-temperature simulation, the Python script program of the present invention needs to be executed to achieve the combination with the open source molecular dynamics simulation software LAMMPS:

[0073] ① Read the solidified atomic model, perform a 2ps molecular dynamics simulation on it using the NPT ensemble under 1800K, 0.6GPa pyrolysis conditions, make the solidified atomic model undergo pyrolysis reaction, and output the molecular dynamics simulation trajectory file;

[0074] ② The Python script program of the present invention is used to read the last frame structure of the previous trajectory file as the pyrolysis intermediate structure, and the generated hydrogen pyrolysis product is identified by the hydrogen-hydrogen bonding criterion, and the atomic number constituting the hydrogen product is recorded; the generated methane pyrolysis product is identified by the carbon-hydrogen bonding criterion, and the atomic number constituting the methane pyrolysis product is recorded; the criterion for judging the generation of hydrogen and methane molecules in the pyrolysis product is: hydrogen product, hydrogen-silicon, hydrogen-carbon, hydrogen-oxygen bond lengths are respectively greater than Methane products, carbon atoms must form bonds with surrounding atoms such that the shortest carbon-carbon, carbon-silicon, and carbon-oxygen bonds are longer than And the coordination number of the carbon-hydrogen bond must be equal to 4;

[0075] ③ Using the Python script of the present invention, the hydrogen and methane molecular products of the intermediate structure of the pyrolysis are deleted, and a new structure file is generated and transferred to the molecular dynamics pyrolysis simulation in step ①; the pyrolysis process continuously cycles through steps ①-③ until the methyl and hydrogen functional groups of the side chains of the sol molecules are completely removed, and the latest structure file is used as the atomic structure model after pyrolysis;

[0076] 6) The post-pyrolysis atomic structure model obtained in step 5) is relaxed at 3000 K for not less than 500 ps, ​​and annealed to room temperature and pressure at a rate of 0.1 K / fs. Finally, the NPT ensemble is relaxed at room temperature and pressure for not less than 100 ps to obtain a fully balanced hydrolysis-pyrolysis amorphous SiOC atomic model.

[0077] Example:

[0078] In this example, considering that MTMS and DMDMS are easily hydrolyzed in solution, the precursor small molecules are simplified to MTMS'(CH3Si(OH)3) and DMDMS'((CH3)2Si(OH)2), see Figure 2 . In this example, the mass ratio of MTMS' / DMDMS' is selected as 5:1 (molar ratio is approximately equal to 49:10). First, 98 MTMS' and 20 DMDMS' molecules are randomly mixed and placed in a cubic box that is periodic in three directions to construct a sol small molecule model. The implementation method of the present invention based on molecular dynamics simulation to realize the precursor hydrolysis-pyrolysis method to construct an amorphous atomic model, the specific steps are as follows:

[0079] Step 1: With the help of the open source molecular dynamics simulation software LAMMPS, a sol small molecule model with a MTMS' / DMDMS' molar ratio of approximately 49:10 was constructed by melt annealing method, and the constructed structural model was fully relaxed for no less than 100ps using the NPT ensemble under 300K and 0.1MPa conditions to achieve complete equilibrium in structure, energy and density, thereby obtaining a stable precursor atomic model;

[0080] Step 2: The obtained precursor atomic model is heated to the hydrolysis temperature of 400K, and the NPT ensemble is relaxed for 100ps under 0.1MPa to obtain the precursor atomic model under hydrolysis conditions;

[0081] Step 3: Perform hydrolysis simulation on the precursor atomic model obtained in the previous step. When performing the hydrolysis simulation, the Python script program of the present invention needs to be executed to achieve the combination with the open source molecular dynamics simulation software LAMMPS:

[0082] ① Read the precursor atomic model, perform 2ps molecular dynamics simulation on it using NPT ensemble under 400K, 0.1MPa hydrolysis conditions, make the sol molecules undergo hydrolysis reaction, and output the molecular dynamics simulation trajectory file;

[0083] ② The Python script of the present invention is used to read the last frame structure of the previous trajectory file as the hydrolysis intermediate structure, identify the generated water molecule hydrolysis products through the bonding criterion of oxygen and hydrogen atoms, and record the atomic numbers of the water molecules; the criterion for judging the generation of water molecules in the hydrolysis product must simultaneously meet the following conditions: the oxygen-silicon, oxygen-carbon, and oxygen-oxygen bond lengths are respectively greater than The coordination number of the oxygen-hydrogen bond must be equal to 2;

[0084] ③ The water molecule products of the hydrolysis intermediate structure are deleted with the help of the Python script program of the present invention, and a new structure file is generated and passed to the molecular dynamics hydrolysis simulation in step ①; if steps ①-③ are cycled a certain number of times and no new water molecules are generated, it indicates that the hydrolysis reaction is complete, and the latest structure file is used as the atomic structure model after hydrolysis, such as Figure 3 (left) as shown;

[0085] Step 4: The atomic structure model after hydrolysis obtained in step 3) is subjected to molecular dynamics annealing simulation at a rate of 0.1K / fs, and the NPT ensemble is relaxed for 100ps at 300K and 0.1MPa to obtain a fully balanced precursor solidification atomic model;

[0086] Step 5: Perform high-temperature pyrolysis calculation on the precursor solidification atomic model obtained in the previous step. When performing high-temperature simulation, the Python script program of the present invention needs to be executed to achieve the combination with the open source molecular dynamics simulation software LAMMPS:

[0087] ① Read the solidified atomic model, perform a 2ps molecular dynamics simulation on it using the NPT ensemble under 1800K, 0.6GPa pyrolysis conditions, make the solidified atomic model undergo pyrolysis reaction, and output the molecular dynamics simulation trajectory file;

[0088] ② The Python script program of the present invention is used to read the last frame structure of the previous trajectory file as the pyrolysis intermediate structure, and the generated hydrogen pyrolysis product is identified by the hydrogen-hydrogen bonding criterion, and the atomic number constituting the hydrogen product is recorded; the generated methane pyrolysis product is identified by the carbon-hydrogen bonding criterion, and the atomic number constituting the methane pyrolysis product is recorded; the criterion for judging the generation of hydrogen and methane molecules in the pyrolysis product is: hydrogen product, hydrogen-silicon, hydrogen-carbon, hydrogen-oxygen bond lengths are respectively greater than Methane products, carbon atoms must form bonds with surrounding atoms such that the shortest carbon-carbon, carbon-silicon, and carbon-oxygen bonds are longer than And the coordination number of the carbon-hydrogen bond must be equal to 4;

[0089] ③ The hydrogen and methane molecular products of the pyrolysis intermediate structure are deleted with the help of the Python script program of the present invention, and a new structure file is generated and passed to the molecular dynamics pyrolysis simulation in step ①; the pyrolysis process continuously cycles through steps ①-③ until the methyl and hydrogen functional groups of the side chains of the sol molecules are completely removed, and the latest structure file is used as the atomic structure model after pyrolysis, such as Figure 3 (middle) shown;

[0090] Step 6: The pyrolysis atomic structure model obtained in step 5) is relaxed at 3000K for 500ps, and annealed to room temperature and pressure at a rate of 0.1K / fs. Finally, the NPT ensemble is relaxed for 100ps at room temperature and pressure to obtain a fully balanced hydrolysis-pyrolysis amorphous SiOC atomic model, as shown in FIG. Figure 3 As shown in (right), it can be seen that there are a large number of free carbon networks in the amorphous SiOC structure produced by the hydrolysis-pyrolysis method simulation.

[0091] In summary, the present invention discloses a method for constructing an amorphous atomic model based on molecular dynamics simulation to realize the precursor hydrolysis-pyrolysis method, which utilizes the characteristics that the main products of the precursor hydrolysis and pyrolysis process are water, hydrogen and methane, respectively. Through the written Python script program, a reasonable criterion is selected to judge the bonding distance between atoms, identify the generated products, and realize batch and cyclic molecular dynamics simulation to obtain an amorphous SiOC atomic model. The present invention finally realizes the automatic and batch combination with the open source molecular dynamics calculation software LAMMPS, eliminates the influence of human subjective factors, improves the calculation efficiency, saves the time cost of scientific researchers, and avoids the omissions caused by a large number of operations. In addition, the sol small molecules can form a good network skeleton structure after hydrolysis and solidification, slowing down the escape velocity of gas products, and can construct an amorphous SiOC model with a higher free carbon content, thereby improving the amorphous-nanocrystalline interface density of the material.

[0092] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis, characterized in that: The following steps are involved: 1) Constructing the precursor atomic model by melt annealing method; 2) heating the obtained precursor atomic model to the hydrolysis temperature for relaxation to obtain the precursor atomic model under the hydrolysis condition; 3) Performing hydrolysis simulation on the precursor atomic model to obtain the atomic structure model after hydrolysis; 4) subjecting the atomic structure model after hydrolysis obtained in step 3) to molecular dynamics annealing simulation, and setting a relaxation time at a constant temperature and constant pressure to obtain a balanced precursor solidified atomic model; 5) Perform high-temperature pyrolysis calculation on the precursor solidification atomic model to obtain the atomic structure model after pyrolysis; 6) The atomic structure model after pyrolysis obtained in step 5) is subjected to molecular dynamics annealing simulation, and is relaxed for a set time at a constant temperature and constant pressure to obtain a fully balanced hydrolysis-pyrolysis amorphous SiOC atomic model.

2. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 1, characterized in that: The hydrolysis simulation of the precursor atomic model to obtain the atomic structure model after hydrolysis comprises the following steps: ① Read the precursor atomic model, perform molecular dynamics simulation on it at the hydrolysis temperature for a set time, make the sol molecules undergo hydrolysis reaction, and output the molecular dynamics simulation trajectory file; ② Read the last frame structure of the molecular dynamics simulation trajectory file as the hydrolysis intermediate structure, identify the generated water molecule hydrolysis products through the bonding criterion of oxygen-hydrogen atoms, and record the atomic numbers of the water molecules; ③ Delete the water molecule products of the intermediate structure of hydrolysis, re-arrange the atomic numbers in sequence, and generate a new structure file, which is passed as the precursor atomic model to step ① for molecular dynamics hydrolysis simulation; if no new water molecules are generated, it indicates that the hydrolysis reaction is complete, and the latest structure file is used as the atomic structure model after hydrolysis.

3. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 2, characterized in that: The water molecule hydrolysis products generated by the oxygen-hydrogen atom bonding criterion are identified under the following identification conditions: The bond lengths of oxygen-silicon, oxygen-carbon, and oxygen-oxygen are respectively greater than The coordination number of the oxygen-hydrogen bond must be equal to 2.

4. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 1, characterized in that: In step 5), the high temperature pyrolysis calculation is performed on the precursor solidified atomic model to obtain the atomic structure model after pyrolysis, which includes the following steps: 5.1) Reading the precursor solidification atomic model, performing molecular dynamics simulation on it at the pyrolysis temperature for a set time, causing the precursor solidification atomic model to undergo pyrolysis reaction, and outputting a molecular dynamics simulation trajectory file; 5.2) reading the last frame structure of the molecular dynamics simulation trajectory file of step 5.1) as the pyrolysis intermediate structure; identifying the generated hydrogen pyrolysis products by hydrogen-hydrogen bonding criterion, and recording the atomic numbers constituting the hydrogen products; identifying the generated methane pyrolysis products by carbon-hydrogen bonding criterion, and recording the atomic numbers constituting the methane pyrolysis products; 5.3) Delete the hydrogen pyrolysis products and methane pyrolysis products of the pyrolysis intermediate structure, generate a new structure file, and pass it to the molecular dynamics pyrolysis simulation in step 5.1) as the precursor solidification atomic model; when the methyl and hydrogen functional groups of the side chains of the sol molecules are completely removed, use the latest structure file as the atomic structure model after pyrolysis.

5. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 4, characterized in that: The generated hydrogen pyrolysis products are identified by the hydrogen-hydrogen bonding criterion, and the generated methane pyrolysis products are identified by the carbon-hydrogen bonding criterion. The identification conditions are as follows: Hydrogen pyrolysis products: hydrogen-silicon, hydrogen-carbon, hydrogen-oxygen bond lengths are greater than Methane pyrolysis products: When carbon atoms form bonds with surrounding atoms, the shortest carbon-carbon, carbon-silicon, and carbon-oxygen bond lengths must be greater than And the coordination number of the carbon-hydrogen bond must be equal to 4.

6. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 1, characterized in that: The precursor atomic model is constructed by selecting an NPT ensemble relaxation of no less than 100 ps under the conditions of 300K and 0.1 MPa.

7. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 1, characterized in that: The hydrolysis simulation conditions are 400K, 0.1MPa, and NPT ensemble relaxation is selected for no less than 100ps; the hydrolysis simulation cycle is 400K, 0.1MPa, NPT ensemble, the number of hydrolysis cycle simulations is 1000 times, and each calculation is 2ps.

8. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 1, characterized in that: The atomic structure model after hydrolysis obtained in step 3) is subjected to molecular dynamics annealing simulation, the annealing rate from 400K to 300K is 0.1K / fs, and the NPT ensemble relaxation is selected at 300K and 0.1MPa for not less than 100ps; the high-temperature pyrolysis cycle is 1800K, 0.6GPa, NPT ensemble, and each pyrolysis cycle simulation calculation is 2ps.

9. The molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis according to claim 1, characterized in that: The atomic structure model after pyrolysis obtained in step 5) is subjected to molecular dynamics annealing simulation, heated to 3000K and relaxed for 500ps, and annealed to room temperature and pressure at a rate of 0.1K / fs, and finally relaxed for 100ps using the NPT ensemble.

10. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by the processor, the molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis as described in any one of claims 1 to 9 is implemented.

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