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

Abstract

The application relates to a precursor hydrolysis-pyrolysis amorphous model construction molecular dynamics simulation method, which is characterized in that the main products of the precursor hydrolysis and pyrolysis process are water and hydrogen and methane, a Python script program is written, a reasonable criterion is selected, the bonding distance between atoms is judged, the generated product is identified, batch and cyclic molecular dynamics simulation is realized, and an amorphous SiOC atomic model is obtained. The application finally realizes automatic, batch and 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 mistakes caused by a large number of operations. In addition, after the hydrolysis and solidification of the sol small molecules, a good network skeleton structure can be formed, the escape speed of the gas product is slowed down, a higher free carbon content amorphous SiOC model can be constructed, and the amorphous-nanocrystalline interface density of the material is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of amorphous ceramic material simulation, and relates to a molecular dynamics simulation method for constructing an amorphous model through precursor hydrolysis-pyrolysis, in particular to a method for automatically and batch connecting open source molecular dynamics simulation based on molecular dynamics simulation. BACKGROUND

[0002] Amorphous SiOC exhibits isotropy on a macroscopic scale, but presents inhomogeneity on a micro-nanoscale, and its structure mainly comprises amorphous SiO2 structure, free carbon and mixed silicon tetrahedral structure units between the two interfaces. The types of functional groups contained in the precursor have a significant influence on the composition and structure of the hydrolysis and pyrolysis products, such as Si-H and Si-CH3 groups in PMHS, which can reduce the free carbon content in the products. Therefore, the process of preparing ceramics by precursor pyrolysis is very complex, and it is difficult to completely understand the specific relationship between the composition, structure and performance of SiOC and the structure of the precursor and the preparation process by relying on experimental means only. Therefore, computer simulation can make up for the shortcomings of high-temperature characterization, and can in-situ and quantitatively study the influence of the process of preparing ceramics by precursor pyrolysis on the composition, structure and performance of SiOC by using a suitable simulation method.

[0003] In summary, it is crucial to clarify the influence of the precursor and the hydrolysis-pyrolysis process on the microstructure and comprehensive performance of amorphous SiOC. Nowadays, researchers usually construct amorphous models by using a melting annealing method, that is, the temperature of the system is increased to a high temperature to form a "liquid phase", 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, and finally the amorphous structure is obtained. The annealing process can have different treatment methods, one of which is rapid annealing to keep the structure in a metastable amorphous state, and the other is multi-step annealing to fully relax the structure. However, the melting annealing method can only obtain the influence of element ratio and structure on material performance, and cannot clearly reveal the influence of precursor raw materials and hydrolysis-pyrolysis process on the microstructure and comprehensive performance of materials. SUMMARY

[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 application aims to use the characteristics that the main products of the hydrolysis and pyrolysis process of the precursor are water and hydrogen, and methane, use a Python script program, select a reasonable criterion, 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 application finally realizes the automatic, batch and open source molecular dynamics calculation software LAMMPS, eliminates the influence of human subjective factors, improves the calculation efficiency, saves the time cost of researchers, and avoids mistakes due to a large number of operations.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions to achieve the above-mentioned purpose: a precursor hydrolysis-pyrolysis construction amorphous model molecular dynamics simulation method, comprising the following steps:

[0006] 1) Constructing a precursor atomic model by using a melting annealing method;

[0007] 2) Relaxing the obtained precursor atomic model to a hydrolysis temperature to obtain a precursor atomic model under hydrolysis conditions;

[0008] 3) Hydrolysis simulation of the precursor atomic model to obtain an atomic structure model after hydrolysis;

[0009] 4) Molecular dynamics annealing simulation of the atomic structure model after hydrolysis obtained in step 3), and constant temperature and pressure relaxation for a set time to obtain an equilibrium precursor solidified atomic model;

[0010] 5) High-temperature pyrolysis calculation of the precursor solidified atomic model to obtain an atomic structure model after pyrolysis;

[0011] 6) Molecular dynamics annealing simulation of the atomic structure model after pyrolysis obtained in step 5), and constant temperature and pressure relaxation for a set time 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, and perform molecular dynamics simulation for a set time at a hydrolysis temperature to make the sol molecules undergo a hydrolysis reaction, and output a molecular dynamics simulation trajectory file;

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

[0015] ③ Delete the water molecule product of the hydrolysis intermediate structure, re-sort the atomic numbers in sequence, and generate a new structure file as the precursor atomic model to pass 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 taken as the atomic structure model after hydrolysis.

[0016] The identification of the generated water molecule hydrolysis product through the bonding criterion of oxygen-hydrogen atoms has the following identification conditions:

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

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

[0019] In step 5), the precursor solidification atomic model is subjected to high-temperature pyrolysis calculation to obtain a pyrolyzed atomic structure model, including the following steps:

[0020] 5.1) Read the precursor solidification atomic model, and perform a molecular dynamics simulation at a pyrolysis temperature for a set time to make the precursor solidification atomic model undergo a pyrolysis reaction, and output a molecular dynamics simulation trajectory file;

[0021] 5.2) Read the last frame structure of the molecular dynamics simulation trajectory file of step 5.1) as a pyrolysis intermediate structure; identify the generated hydrogen gas pyrolysis product by a hydrogen-hydrogen bonding criterion, and record the atomic serial numbers constituting the hydrogen gas product; identify the generated methane pyrolysis product by a carbon-hydrogen bonding criterion, and record the atomic serial numbers constituting the methane pyrolysis product;

[0022] 5.3) Delete the hydrogen gas pyrolysis product and the methane pyrolysis product of the pyrolysis intermediate structure, and generate a new structure file as the precursor solidification atomic model for transmission to the molecular dynamics pyrolysis simulation in step 5.1); when the solute molecule side chain methyl and hydrogen functional groups are completely removed, the latest structure file is taken as the pyrolyzed atomic structure model.

[0023] The generated hydrogen gas pyrolysis product is identified by a hydrogen-hydrogen bonding criterion, and the generated methane pyrolysis product is identified by a carbon-hydrogen bonding criterion, and the identification conditions are as follows:

[0024] Hydrogen gas pyrolysis product: hydrogen-silicon, hydrogen-carbon, and hydrogen-oxygen bond lengths are greater than 0.7 A, 0.9 A, and 0.9 A, respectively. Methane pyrolysis product: when the carbon atom bonds with surrounding atoms, the shortest carbon-carbon, carbon-silicon, and carbon-oxygen bond lengths must be greater than 1.5 A, 1.9 A, and 1.9 A, respectively. And the coordination number of the carbon-hydrogen bond must be equal to 4.

[0025] The precursor atomic model is constructed, and the NPT ensemble is selected for relaxation for not less than 100 ps at 300 K and 0.1 MPa.

[0026] The hydrolysis simulation conditions are 400 K and 0.1 MPa, and the NPT ensemble is selected for relaxation for not less than 100 ps; the hydrolysis simulation cycle is 400 K, 0.1 MPa, NPT ensemble, and the hydrolysis cycle simulation number is 1000 times, and each calculation is 2 ps.

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

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

[0029] A computer readable storage medium, the storage medium has a computer program stored thereon, when the computer program is executed by a processor, the precursor hydrolysis-pyrolysis amorphous model construction molecular dynamics simulation method is realized.

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

[0031] 1. By using the characteristics that the main products of the precursor hydrolysis and pyrolysis process are water and hydrogen, respectively, and by using a reasonable criterion to judge the bonding distance between atoms, the hydrolysis and pyrolysis products are identified, batch and cyclic molecular dynamics simulation is realized, and a hydrolysis-pyrolysis amorphous SiOC atomic model is obtained.

[0032] 2. The automatic, batch and molecular dynamics calculation software are combined, the influence of human subjective factors is excluded, the calculation efficiency is improved, the time cost of scientific researchers is saved, and errors caused by a large number of operations are avoided.

[0033] 3. The NPT ensemble is selected in the simulation, the system density can be adjusted in real time according to the type and quantity of the discharged hydrolysis and pyrolysis products, and the error caused by the NVT ensemble unable to adjust the system volume is avoided.

[0034] 4. The amorphous SiOC atomic model obtained by the method exhibits the characteristics of amorphous SiOC prepared by the precursor hydrolysis-pyrolysis method in experiments, and a large number of free carbon network structures are generated in the amorphous matrix due to the crosslinking of the precursor skeleton and the decomposition of methane gas.

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

[0036] Figure 1A flowchart for constructing an amorphous atomic model by precursor hydrolysis-pyrolysis method based on molecular dynamics simulation;

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

[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 application will be further described in detail below with reference to the accompanying drawings and examples.

[0040] The application discloses a method for constructing an amorphous atomic model by precursor hydrolysis-pyrolysis method based on molecular dynamics simulation, and belongs to the field of amorphous ceramic material simulation. The method takes advantage of the characteristics that the main products of the precursor hydrolysis and pyrolysis process are water and hydrogen, and methane, uses a Python script program, selects reasonable criteria, judges the bonding distance between atoms, identifies the generated products, realizes batch and cyclic molecular dynamics simulation, and obtains an amorphous SiOC atomic model. The method finally realizes the automatic use of the open-source molecular dynamics calculation software LAMMPS, eliminates the influence of human subjective factors, improves the calculation efficiency, saves the time cost of researchers, and avoids mistakes caused by a large number of operations. In addition, after the hydrolysis and solidification of the sol small molecules, a good network skeleton structure can be formed, the escape speed of the gas products is slowed down, a higher free carbon content amorphous SiOC model can be constructed, and the density of the amorphous-nanocrystalline interface of the material is improved.

[0041] The application 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 using the melting annealing method, and the constructed structure model is fully relaxed at normal temperature and pressure, so that the structure, energy and density are fully balanced, thereby obtaining a stable precursor atomic model;

[0043] 2) The obtained precursor atomic model is heated to a hydrolysis temperature and fully relaxed for a certain time, thereby obtaining a precursor atomic model under hydrolysis conditions;

[0044] 3) The precursor atomic model obtained in the above step is subjected to hydrolysis simulation, and the Python script program of the application needs to be executed during the hydrolysis simulation, thereby realizing the use of the open-source molecular dynamics simulation software LAMMPS:

[0045]

[0046] ②The last frame structure of the trajectory file in the step is read by the Python script program of the application as a hydrolysis intermediate structure, and the generated water molecule hydrolysis product is identified by the bonding criterion of oxygen and hydrogen atoms, and the atomic serial numbers constituting the water molecule are recorded;

[0047] ③The water molecule product of the hydrolysis intermediate structure is deleted by the Python script program of the application, and a new structure file is generated and transmitted to the molecular dynamics hydrolysis simulation in the first step; if the steps 1-3 are repeated for a certain number of times and no new water molecule is generated, it is indicated that the hydrolysis reaction is complete, and the latest structure file is taken as the atomic structure model after hydrolysis;

[0048] 4) The atomic structure model after hydrolysis obtained in the step 3) is subjected to molecular dynamics annealing simulation, and is relaxed for a certain time under constant temperature and pressure to obtain a fully balanced precursor solidified atomic model;

[0049] 5) The precursor solidified atomic model obtained in the above step is subjected to high-temperature pyrolysis calculation, and the Python script program of the application needs to be executed during high-temperature simulation to realize the combination with the open-source molecular dynamics simulation software LAMMPS:

[0050] ①The solidified atomic model is read, and molecular dynamics simulation is performed on the solidified atomic model for a certain time under pyrolysis temperature, so that the solidified atomic model undergoes pyrolysis reaction, and a molecular dynamics simulation trajectory file is output;

[0051] ②The last frame structure of the trajectory file in the step is read by the Python script program of the application as a hydrolysis intermediate structure, and the generated water molecule hydrolysis product is identified by the bonding criterion of oxygen and hydrogen atoms, and the atomic serial numbers constituting the water molecule are recorded;

[0052] ③The water molecule product of the hydrolysis intermediate structure is deleted by the Python script program of the application, and a new structure file is generated and transmitted to the molecular dynamics hydrolysis simulation in the first step; if the steps 1-3 are repeated for a certain number of times and no new water molecule is generated, it is indicated that the hydrolysis reaction is complete, and the latest structure file is taken as the atomic structure model after hydrolysis;

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

[0054] ​Preferably, in step 1), the system is selected to relax for no less than 100 ps under the condition of 300 K, 0.1 MPa using the NPT ensemble;

[0055] Preferably, in step 2), the hydrolysis simulation condition is set to 400 K, 0.1 MPa, and the system is selected to relax for no less than 100 ps under the condition of 400 K, 0.1 MPa using the NPT ensemble;

[0056] Preferably, in step 3), the hydrolysis cycle simulation method is set to 400 K, 0.1 MPa, the NPT ensemble, and the hydrolysis cycle simulation number is 1000 times, and each calculation is 2 ps; 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 greater than 1.5 Å, 1.5 Å and 1.5 Å, respectively;

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

[0059] Preferably, in step 4), the annealing rate is 0.1 K / fs from 400 K to 300 K, and the system is selected to relax for no less than 100 ps under the condition of 300 K, 0.1 MPa using the NPT ensemble;

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

[0061] ① Hydrogen pyrolysis product: the bond lengths of hydrogen-silicon, hydrogen-carbon and hydrogen-oxygen are greater than 1.5 Å, 1.5 Å and 1.5 Å, respectively;

[0062] ② Methane pyrolysis product: when the carbon atom bonds with the surrounding atoms, the shortest carbon-carbon, carbon-silicon and carbon-oxygen bond lengths must be greater than 1.5 Å, 1.5 Å and 1.5 Å, respectively; and the coordination number of the carbon-hydrogen bond must be equal to 4;

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

[0064] Referring to Figure 1 , combined with the hydrolysis-pyrolysis method, the flow chart for constructing an amorphous atomic model is illustrated, which illustrates the implementation method for constructing an amorphous atomic model based on the precursor hydrolysis-pyrolysis method by molecular dynamics simulation, which includes the following steps:

[0065] 1) By means of the open source molecular dynamics simulation software LAMMPS, a sol small molecule model of a certain molar ratio is constructed by means of a melting annealing method, and the structural model constructed is selected under the condition of 300K, 0.1MPa and NPT ensemble for full relaxation of not less than 100ps, so that the structure, energy and density are fully balanced, so as to obtain a stable precursor atomic model;

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

[0067] 3) The precursor atomic model obtained in the above step is subjected to hydrolysis simulation, and the Python script program of the application needs to be executed during the hydrolysis simulation to realize the combination with the open source molecular dynamics simulation software LAMMPS:

[0068] ① Read the precursor atomic model, and perform 2ps of molecular dynamics simulation under the condition of 400K, 0.1MPa hydrolysis and NPT ensemble, so that the sol molecules are subjected to hydrolysis reaction, and a molecular dynamics simulation trajectory file is output;

[0069] ② The last frame structure of the trajectory file in the above step is read by the Python script program of the application as a hydrolysis intermediate structure, the generated water molecule hydrolysis product is identified by the bonding criterion of oxygen and hydrogen atoms, and the atomic numbers constituting the water molecules are recorded; The criterion for judging the generation of the hydrolysis product water molecule must meet the following conditions at the same time: The coordination number of the oxygen-hydrogen bond must be equal to 2;

[0070] ③ The water molecule product of the hydrolysis intermediate structure is deleted by means of the Python script program of the application, and a new structure file is generated and transmitted to the molecular dynamics hydrolysis simulation in the first step; If the steps ①-③ are repeated for a certain number of times, and no new water molecule is generated, it is indicated that the hydrolysis reaction is complete, and the latest structure file is taken as the atomic structure model after hydrolysis;

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

[0072] 5) The precursor solidification atomic model obtained in the above step is subjected to high temperature pyrolysis calculation, and the Python script program of the application needs to be executed during the high temperature simulation to realize the combination with the open source molecular dynamics simulation software LAMMPS:

[0073] ① Read the solidified atomic model, and perform 2ps of molecular dynamics simulation on the solidified atomic model under the pyrolysis condition of 1800K, 0.6GPa using NPT ensemble, so that the solidified atomic model is subjected to pyrolysis reaction, and a molecular dynamics simulation trajectory file is output;

[0074] ② The last frame structure of the trajectory file in the step 1 is read as the pyrolysis intermediate structure by the Python script program of the present application, the generated hydrogen pyrolysis product is identified by the bonding criterion of hydrogen-hydrogen, and the atomic serial numbers constituting the hydrogen product are recorded; the generated methane pyrolysis product is identified by the bonding criterion of carbon-hydrogen, and the atomic serial numbers constituting the methane pyrolysis product are recorded; the generation criterion of the pyrolysis products hydrogen and methane is that the bond lengths of hydrogen-silicon, hydrogen-carbon and hydrogen-oxygen of the hydrogen product are greater than 1.5A, 1.5A and 1.5A respectively, and the bond lengths of carbon-carbon, carbon-silicon and carbon-oxygen of the methane product are greater than 1.5A, 1.5A and 1.5A respectively.

[0075] ③ The hydrogen and methane molecule products of the pyrolysis intermediate structure are deleted by the Python script program of the present application, and a new structure file is generated and transmitted to the molecular dynamics pyrolysis simulation in the step 1; the steps 1-3 are continuously cycled until the methyl and hydrogen functional groups of the sol molecule side chain are completely removed, and the latest structure file is taken as the atomic structure model after pyrolysis.

[0076] 6) The atomic structure model after pyrolysis obtained in the step 5 is relaxed at 3000K for not less than 500ps, and annealed to normal temperature and pressure state at a rate of 0.1K / fs, and finally relaxed for not less than 100ps using NPT ensemble under normal temperature and pressure conditions, so as to obtain a fully equilibrated hydrolysis-pyrolysis amorphous SiOC atomic model.

[0077] Embodiment:

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

[0079] ​​First step: with the help of open source molecular dynamics simulation software LAMMPS, a sol small molecule model with the molar ratio of MTMS' / DMDMS' being about 49:10 is constructed by using the melting annealing method, and the constructed structure model is selected to be fully relaxed for not less than 100 ps under the condition of 300 K, 0.1 MPa, so that the structure, energy and density reach complete balance, thereby obtaining a stable precursor atomic model;

[0080] Second step: the obtained precursor atomic model is warmed to a hydrolysis temperature of 400 K, and is selected to be relaxed for 100 ps under the condition of 0.1 MPa by using the NPT ensemble, thereby obtaining a precursor atomic model under the hydrolysis condition;

[0081] Third step: the precursor atomic model obtained in the above step is subjected to hydrolysis simulation, and the Python script program of the application needs to be executed when the hydrolysis simulation is performed, so as to realize the combination with the open source molecular dynamics simulation software LAMMPS:

[0082] ①The precursor atomic model is read, and is subjected to 2 ps of molecular dynamics simulation under the condition of 400 K, 0.1 MPa hydrolysis by using the NPT ensemble, so that the sol molecules are subjected to hydrolysis reaction, and a molecular dynamics simulation trajectory file is output;

[0083] ②The Python script program of the application reads the last frame structure of the trajectory file in the above step as a hydrolysis intermediate structure, identifies the generated water molecule hydrolysis product through the bonding criterion of oxygen and hydrogen atoms, and records the atomic serial numbers constituting the water molecules; the criterion for judging the generation of the water molecule hydrolysis product must simultaneously satisfy the following conditions: The coordination number of the oxygen-hydrogen bond must be equal to 2;

[0084] ③The Python script program of the application deletes the water molecule product of the hydrolysis intermediate structure, and generates a new structure file which is transmitted to the molecular dynamics hydrolysis simulation in the first step; if the steps ①-③ are repeated for a certain number of times, and no new water molecule is generated, it is indicated that the hydrolysis reaction is complete, and the latest structure file is taken as the atomic structure model after hydrolysis, as shown in Figure 3 (left);

[0085] Fourth step: the atomic structure model after hydrolysis obtained in the third step is subjected to molecular dynamics annealing simulation at a rate of 0.1 K / fs, and is selected to be relaxed for 100 ps under the condition of 300 K, 0.1 MPa by using the NPT ensemble, thereby obtaining a fully balanced precursor solidification atomic model;

[0086] Fifth step: the precursor solidification atomic model obtained in the above step is subjected to high-temperature pyrolysis calculation, and the Python script program of the application needs to be executed when the high-temperature simulation is performed, so as to realize the combination with the open source molecular dynamics simulation software LAMMPS:

[0087] ① Read the solidification atomic model, and use NPT ensemble to carry out 2ps molecular dynamics simulation under the pyrolysis condition of 1800K, 0.6GPa, so that the solidification atomic model is pyrolyzed, and a molecular dynamics simulation trajectory file is output;

[0088] ② The last frame structure of the trajectory file in the step 1 is read as the pyrolysis intermediate structure by the Python script program of the present application, the generated hydrogen pyrolysis product is identified by the bonding criterion of hydrogen-hydrogen, and the atomic serial numbers constituting the hydrogen product are recorded; the generated methane pyrolysis product is identified by the bonding criterion of carbon-hydrogen, and the atomic serial numbers constituting the methane pyrolysis product are recorded; the generation criterion of the pyrolysis products hydrogen and methane is that the bond length of hydrogen-silicon, hydrogen-carbon, hydrogen-oxygen of the hydrogen product is greater than 1.5A, respectively, and the bond length of carbon-carbon, carbon-silicon, carbon-oxygen of the methane product is greater than 1.5A, respectively. And the coordination number of carbon-hydrogen bond must be equal to 4.

[0089] ③ The hydrogen and methane molecules of the pyrolysis intermediate structure are deleted by the Python script program of the present application, and a new structure file is generated and transmitted to the molecular dynamics pyrolysis simulation in the step 1; the pyrolysis process is continuously cycled 1-3 steps until the methyl and hydrogen functional groups of the sol molecular side chain are completely removed, and the latest structure file is taken as the atomic structure model after pyrolysis, as shown in Figure 3 (centre).

[0090] Step 6: The atomic structure model after pyrolysis obtained in the step 5 is relaxed at 3000K for 500ps, and annealed to normal temperature and pressure state at a rate of 0.1K / fs, and finally relaxed for 100ps at normal temperature and pressure condition by using NPT ensemble, so that a fully balanced hydrolysis-pyrolysis amorphous SiOC atomic model is obtained, as shown in Figure 3 (right).It can be seen from the figure that there is a large amount of free carbon network in the amorphous SiOC structure simulated by the hydrolysis-pyrolysis method.

[0091] To sum up, the application discloses a method for constructing an amorphous atomic model by precursor hydrolysis-pyrolysis based on molecular dynamics simulation, which uses the characteristics that the main products of the precursor hydrolysis and pyrolysis process are water and hydrogen, and methane, uses a Python script program, selects reasonable criteria, judges the bonding distance between atoms, identifies the generated products, realizes batch and cyclic molecular dynamics simulation, and obtains an amorphous SiOC atomic model. The application finally realizes the automatic use of the open source molecular dynamics calculation software LAMMPS in batches, eliminates the influence of human subjective factors, improves the calculation efficiency, saves the time cost of researchers, and avoids the mistakes 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 speed of the gas products, and can construct an amorphous SiOC model with higher free carbon content, and improve the amorphous-nanocrystalline interface density of the material.

[0092] The above content only illustrates the technical idea of the application and cannot limit the protection scope of the application. Any modification made according to the technical idea of the application on the basis of the technical scheme falls within the protection scope of the claims of the application.

Claims

1. A method of molecular dynamics simulation for constructing an amorphous model of a precursor hydrolysis-pyrolysis, characterized in that, The method comprises the following steps: 1) constructing a precursor atomic model by using a melting annealing method; 2) relaxing the obtained precursor atomic model to a hydrolysis temperature to obtain a precursor atomic model under a hydrolysis condition; 3) performing a hydrolysis simulation on the precursor atomic model to obtain an atomic structure model after hydrolysis; 4) performing a molecular dynamics annealing simulation on the atomic structure model after hydrolysis obtained in step 3), and relaxing at a constant temperature and pressure for a set time to obtain an equilibrium precursor solidification atomic model; 5) performing a high-temperature pyrolysis calculation on the precursor solidification atomic model to obtain an atomic structure model after pyrolysis; 6) performing a molecular dynamics annealing simulation on the atomic structure model after pyrolysis obtained in step 5), and relaxing at a constant temperature and pressure for a set time to obtain a fully balanced hydrolysis-pyrolysis amorphous SiOC atomic model; In step 5), the high-temperature pyrolysis calculation on the precursor solidification atomic model to obtain an atomic structure model after pyrolysis comprises the following steps: 5.1) reading the precursor solidification atomic model, performing a molecular dynamics simulation on the precursor solidification atomic model at a pyrolysis temperature for a set time, making the precursor solidification atomic model undergo a pyrolysis reaction, and outputting a molecular dynamics simulation trajectory file; 5.2) reading the last frame structure of the molecular dynamics simulation trajectory file in step 5.1) as a pyrolysis intermediate structure; identifying the generated hydrogen gas pyrolysis product by a hydrogen-hydrogen bonding criterion, and recording the atomic serial numbers constituting the hydrogen gas product; identifying the generated methane pyrolysis product by a carbon-hydrogen bonding criterion, and recording the atomic serial numbers constituting the methane pyrolysis product; 5.3) deleting the hydrogen gas pyrolysis product and the methane pyrolysis product of the pyrolysis intermediate structure, and generating a new structure file as the precursor solidification atomic model for transmission to the molecular dynamics pyrolysis simulation in step 5.1); when the sol molecule side chain methyl and hydrogen functional groups are completely removed, the latest structure file is taken as the atomic structure model after pyrolysis.

2. The method of claim 1, wherein the precursor hydrolysis-pyrolysis constructed amorphous model is a molecular dynamics simulation method, and the precursor hydrolysis-pyrolysis constructed amorphous model is characterized by, The hydrolysis simulation on the precursor atomic model to obtain an atomic structure model after hydrolysis comprises the following steps: ① reading the precursor atomic model, performing a molecular dynamics simulation on the precursor atomic model at a hydrolysis temperature for a set time, making the sol molecule undergo a hydrolysis reaction, and outputting a molecular dynamics simulation trajectory file; ② reading the last frame structure of the molecular dynamics simulation trajectory file as a hydrolysis intermediate structure, identifying the generated water molecule hydrolysis product by an oxygen-hydrogen atom bonding criterion, and recording the atomic serial numbers constituting the water molecule; ③ deleting the water molecule product of the hydrolysis intermediate structure, reordering the atomic serial numbers in sequence, and generating a new structure file as the precursor atomic model for transmission to the molecular dynamics hydrolysis simulation in step ①; if no new water molecule is generated, it indicates that the hydrolysis reaction is complete, and the latest structure file is taken as the atomic structure model after hydrolysis.

3. The method of claim 2, wherein the precursor hydrolysis-pyrolysis constructed amorphous model is a molecular dynamics simulation method, characterized in that, The identification condition of the generated water molecule hydrolysis product by the oxygen-hydrogen atom bonding criterion is as follows: The bond lengths of oxygen-silicon, oxygen-carbon and oxygen-oxygen are greater than 1.61 Å, 1.872 Å and 1.68 Å, respectively; The coordination number of the oxygen-hydrogen bond must be equal to 2.

4. The method of claim 1, wherein the precursor hydrolysis-pyrolysis constructed amorphous model is a molecular dynamics simulation method, characterized by, 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, and the identification conditions are as follows: Hydrogen pyrolysis products: hydrogen-silicon, hydrogen-carbon, hydrogen-oxygen bond lengths are greater than 1.92 Å, 1.692 Å, 1.5 Å, respectively; Methane pyrolysis products: when the carbon atom bonds with the surrounding atoms, the shortest carbon-carbon, carbon-silicon, carbon-oxygen bond lengths must be greater than 2.064 Å, 2.292 Å, 1.872 Å, respectively, and the coordination number of carbon-hydrogen bond must be equal to 4.

5. The method of claim 1, wherein the precursor hydrolysis-pyrolysis constructed amorphous model is a molecular dynamics simulation method, characterized by, The precursor atomic model is constructed, and the NPT ensemble is selected to relax for not less than 100 ps at 300 K and 0.1 MPa.

6. The method of claim 1, wherein the precursor hydrolysis-pyrolysis constructed amorphous model is a molecular dynamics simulation method, characterized by, The hydrolysis simulation conditions are 400 K and 0.1 MPa, and the NPT ensemble is selected to relax for not less than 100 ps; the hydrolysis simulation cycle is 400 K and 0.1 MPa, and the NPT ensemble is selected, and the hydrolysis cycle simulation is 1000 times, and each calculation is 2 ps.

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

8. The method of claim 1, wherein the precursor hydrolysis-pyrolysis constructed amorphous model is a molecular dynamics simulation method, and the method further comprises: The atomic structure model obtained in step 5) is subjected to molecular dynamics annealing simulation, and the temperature is raised to 3000 K and relaxed for 500 ps, and then annealed to room temperature and pressure state at a rate of 0.1 K / fs, and finally relaxed for 100 ps by using the NPT ensemble. ​ 9. A computer-readable storage medium, characterized in that, The storage medium has a computer program stored thereon, and when the computer program is executed by the processor, the molecular dynamics simulation method for constructing an amorphous model by precursor hydrolysis-pyrolysis is realized.

Images