CN111223530A - Research method for diffusion coefficient of water vapor and oxygen in amorphous silicon dioxide - Google Patents

Research method for diffusion coefficient of water vapor and oxygen in amorphous silicon dioxide Download PDF

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CN111223530A
CN111223530A CN202010024866.1A CN202010024866A CN111223530A CN 111223530 A CN111223530 A CN 111223530A CN 202010024866 A CN202010024866 A CN 202010024866A CN 111223530 A CN111223530 A CN 111223530A
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孙志刚
陈壮壮
陈西辉
宋迎东
牛序铭
熊严
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Nanjing University of Aeronautics and Astronautics
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Abstract

The invention discloses a research method for diffusion coefficients of water vapor and oxygen in amorphous silicon dioxide, which comprises the following steps: the method comprises the following steps: establishing an initial model by using Material Studio, and setting atom grouping and charge number; step two: compiling a script by using lammps to simulate the melting process of the silicon dioxide; step three: setting simulation parameters to simulate the diffusion process of water oxygen in amorphous silicon dioxide; step four: processing and analyzing data; the method can accurately and effectively calculate the diffusion coefficients of water vapor and oxygen in the amorphous silicon dioxide, and lays a foundation for the establishment of an oxidation kinetic model; the method analyzes the atomic diffusion process from the micro-nano scale, can clearly and visually observe the atomic position change, and has novel means; the method is suitable for simulation in different environments, overcomes the defects of harsh experimental research conditions, huge consumption and the like, and is more economic and safe.

Description

Research method for diffusion coefficient of water vapor and oxygen in amorphous silicon dioxide
Technical Field
The invention belongs to the technical field of diffusion coefficient research, and particularly relates to a method for researching diffusion coefficients of water vapor and oxygen in amorphous silicon dioxide.
Background
The continuous silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiC/SiC composite) has the characteristics of high specific strength, specific stiffness, high temperature resistance, corrosion resistance, low density and the like, can effectively realize weight reduction of hot end components, and is an important candidate material for the hot end components of the aircraft engine. The aircraft engine takes aviation kerosene as main fuel, and the main component of the aviation kerosene is hydrocarbon (C)xHy)。CxHyAnd the combustion of the external air stream from the compressor produces large amounts of water vapor (about 10%) and carbon oxides. When the SiC/SiC composite material is rich in oxygen (O)2) And water vapor (H)2O) in a high-temperature (900-1300 ℃ C.) environment, the SiC matrix and the fibers neutralize O in the environment2React to form amorphous SiO2Formation of a dense oxide film, H2O will react with SiO2Reaction to form Si (OH)4Gas, so that SiO2The layer thickness becomes thinner. On the other hand, H2O and O2Diffusion into SiO2The layer reacts with the SiC matrix and fibers inside, causing a rapid decay in its mechanical properties, which in turn leads to a reduction in the life of the material.
The diffusion/interface cooperative control theory shows that O2And H2O through SiO2Layer reaches SiO2The diffusion rate of the SiC interface greatly determines the oxidation rate of the internal SiC, so that O is accurately simulated2And H2O in amorphous SiO2The diffusion rate is important for establishing an oxidation dynamic model of the material, and a solid theoretical basis is laid for further researching the mechanical property of the SiC/SiC composite material in the service environment of the aircraft engine.
In the prior art, patent CN 108304677A' is directed to analyzing the diffusion of contaminants in the pores of a porous carbon materialA simulation method for analyzing the diffusion performance of pollutants in the pores of a porous carbon material is disclosed, a molecular dynamics simulation method is utilized to obtain the relation between the geometric structure of the internal pore channels of the adsorbent and the diffusion rate of the pollutants, but the diffusion of the pollutants is based on pore substances and is not suitable for a compact structure. Patent CN110021380A "a method for exploring diffusion properties of atoms in a glass system based on molecular dynamics simulation" discloses a method for exploring diffusion properties of atoms in a glass system by statistical analysis of glass structure at different temperatures based on molecular dynamics simulation, but the method is limited to self-diffusion of glass, unlike the case where a mixed gas diffuses in an amorphous substance. The article Molecular Dynamics of Water Structure and Diffusion in Silica Nanopores at 298K carries out a Molecular Dynamics study of liquid water Diffusion in Silica Nanopores with diameters in the range of 1-4 nm. It was shown that in this range, the blocking resulted in the disappearance of water resembling a bulk liquid, and finally the diffusion coefficient was found to be 10-9m2In the order of/s. However, the method is only suitable for simulating the diffusion of liquid water in pores at normal temperature and is not suitable for simulating O in high-temperature environment2And H2O in amorphous SiO2In the process of (1). The paper 'carbon dioxide molecular dynamics simulation of dense silicon dioxide surface' develops the structure and the property of carbon dioxide on the surface of amorphous silicon dioxide, and is very helpful for the process mechanism of cleaning microelectronics by supercritical carbon dioxide, but the method is not suitable for the environment of water-oxygen coupling in the combustion chamber of an aircraft engine. The article Transport of rare gases and molecular water in fused silica by molecular dynamics simulation investigated the kinetics and diffusivity of noble gases and molecular water in fused silica. The results show that the diffusion rates of the noble gases studied differ by less than an order of magnitude, with the smaller the size of the noble gas, the greater its diffusion rate. However, this method is only suitable for simulating the presence of water vapor and noble gases in molten SiO2Medium diffusion, not suitable for studying water vapor and oxygen in amorphous SiO2In the process of (1).
Therefore, it is necessary to establish a ring that can effectively simulate high temperatureAmbient water vapor and oxygen in amorphous SiO2Method of diffusion coefficient.
Disclosure of Invention
In order to solve the problem that the diffusion coefficients of water vapor and oxygen in amorphous silica cannot be effectively calculated in the prior art, the invention provides a research method for the diffusion coefficients of water vapor and oxygen in amorphous silica, which adopts a molecular dynamics method to establish a simulation method for the diffusion process of water oxygen in amorphous silica in a high-temperature (1000-.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for researching the diffusion coefficient of water vapor and oxygen in amorphous silicon dioxide comprises the following steps:
the method comprises the following steps: establishing an initial model by using Material Studio, and setting atom grouping and charge number;
step two: compiling a script by using lammps to simulate the melting process of the silicon dioxide;
step three: setting simulation parameters to simulate the diffusion process of water oxygen in amorphous silicon dioxide;
step four: and (4) processing and analyzing data.
Further, the first step comprises the following steps:
α -SiO is derived by using Material Studio software2Establishing supercell (shown in figure 1), connecting Si atoms on the surfaces of two ends in the vertical upward Z direction with O-H bonds to saturate the valence of the Si atoms, expanding the region in the Z direction, placing water molecules and oxygen molecules, establishing a diffusion initial configuration, and setting SiO2And Si atoms, O atoms, H atoms in O-H, O atoms in water molecules and H atoms in water molecules, and exporting the data file.
Further, the second step comprises the following steps:
selecting a simulation process unit, and setting a periodic boundary condition and a truncation radius;
from crystalline SiO2The steps for preparing amorphous silica are as follows: fixed H2O molecule and O2Molecular coordinates, controlling the temperature and pressure of the system, and cooling twice to obtain amorphous SiO2The model obtains a stable structure after fully relaxing the domain;
the amorphous silicon dioxide preparation process adopts Morse function to describe SiO2The interaction between the atoms is carried out,
Figure BDA0002362091270000031
wherein the content of the first and second substances,
Figure BDA0002362091270000032
is the force between any two atoms of Si atom and O atom, D0Gamma is the function parameter of the Morse potential function, RijIs the distance between any two atoms of Si atom, O atom and H atom, R0Cutoff radius, e is 2.7182;
by calculating the amorphous SiO2A Radial Distribution Function (RDF) of the samples, describing a Radial Distribution Function curve of the samples; and comparing the position of the first peak of the system RDF of the sample and the positions of the first valley and the second peak of the Si-O with experimental data, and verifying the correctness of the preparation method.
Further, in the second step, the unit of the simulation process is real, a periodic boundary condition is set, and the truncation radius is
Figure BDA0002362091270000033
Further, in the second step, crystalline SiO is removed2The steps for preparing amorphous silica are as follows: firstly, under an NVT ensemble, after a system is heated to 4000K, the temperature is reduced from 4000K to 300K through a quenching rate of 25K/ps, then under the NPT ensemble, the temperature of a model reaches 4000K through heating of 75ps, and after the model is fully melted to form a constant size, the temperature is reduced to 300K through the quenching rate of 25K/ps under the NPT ensemble; the whole process adopts a time step of 0.5fs, and the pressure is kept at 1.013 multiplied by 105Pa。
Further, the third step includes the following steps:
reading a data file for completing the melting process, and describing the interaction among atoms by adopting a Lennard-Jones potential function:
Figure BDA0002362091270000034
wherein u isLJ(rij) Is short-range acting force between any two atoms of Si atom, O atom and H atom, epsilon and sigma are parameters of L-J potential function, rijIs the interstitial-to-cardiac distance of any two atoms of Si atom, O atom and H atom, rcIs a cutoff radius;
remote force is expressed in coulomb force:
Figure BDA0002362091270000041
wherein E represents a long-range coulomb force, C is a long-range action parameter, qi、qjAny two atomic electric quantities of Si atom, O atom and H atom;
the action potential function parameter between any two atoms adopts Lorentz-Bertholt mixing rule, namely
Figure BDA0002362091270000042
εij＝εi 1/2εj 1/2，σi、εi、σj、εjIs a parameter of same interatomic interaction potential, sigmaij、εijIs the action potential parameter between any two atoms of Si atom, O atom and H atom.
The diffusion of water oxygen in amorphous silica was simulated at 1000 deg.C, 1100 deg.C, 1200 deg.C, 1300 deg.C, respectively.
Further, the fourth step includes the following steps:
the change relation of mean-squared displacement (MSD) of the water oxygen in the amorphous silicon dioxide along with time is obtained in the third step, and the diffusion coefficient is expressed by using Einstein method as follows:
Figure BDA0002362091270000043
wherein D is the diffusion coefficient, ri(t) is the atomic position at time t, and the average value of the same type of atoms is calculated, ri(0) Is the initial time atomic position.
Compared with the prior art, the invention has the following beneficial effects:
(1) the method can accurately and effectively calculate the diffusion coefficients of water vapor and oxygen in the amorphous silicon dioxide, and lays a foundation for the establishment of an oxidation kinetic model;
(2) the method analyzes the atomic diffusion process from the micro-nano scale, can clearly and visually observe the atomic position change, and has novel means;
(3) the method is suitable for simulation in different environments, overcomes the defects of harsh experimental research conditions, huge consumption and the like, and is more economic and safe.
Drawings
FIG. 1 is an initial model diagram;
FIG. 2 is a graph of a radial distribution function;
FIG. 3 (a), (b), (c) and (d) are graphs of MSD as a function of time in amorphous silica for water vapor and oxygen at 1000 deg.C, 1100 deg.C, 1200 deg.C, 1300 deg.C, respectively;
FIG. 4 is a graph of the real-time output of water oxygen in amorphous silica.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1
A method for researching the diffusion coefficient of water vapor and oxygen in amorphous silicon dioxide comprises the following steps:
the method comprises the following steps: establishing an initial model by using Material Studio, and setting atom grouping and charge number;
the first step comprises the following steps:
using Material Studio softPiece, derived α -SiO2Establishing supercell (shown in figure 1), connecting Si atoms on the surfaces of two ends in the vertical upward Z direction with O-H bonds to saturate the valence of the Si atoms, expanding the region in the Z direction, placing water molecules and oxygen molecules, establishing a diffusion initial configuration, and setting SiO2Si atoms, O atoms, H atoms in O-H, O atoms in water molecules and H atoms in water molecules, and exporting the data file;
step two: compiling a script by using lammps to simulate the melting process of the silicon dioxide;
the second step comprises the following steps:
selecting a simulation process unit real, setting a periodic boundary condition, and cutting off a radius of
Figure BDA0002362091270000051
From crystalline SiO2The steps for preparing amorphous silica are as follows: fixed H2O molecule and O2Molecular coordinates, controlling the temperature and pressure of the system, and cooling twice to obtain amorphous SiO2A model; specifically, firstly, under an NVT ensemble, after the system is heated to 4000K, the temperature is reduced from 4000K to 300K through a quenching rate of 25K/ps, then under the NPT ensemble, the temperature of the model reaches 4000K through heating of 75ps, and after the model is fully melted to form a constant size, the temperature is reduced to 300K through the quenching rate of 25K/ps under the NPT ensemble; the whole process adopts a time step of 0.5fs, and the pressure is kept at 1.013 multiplied by 105Pa；
The amorphous silicon dioxide preparation process adopts Morse function to describe SiO2The interaction between the atoms is carried out,
Figure BDA0002362091270000052
wherein the content of the first and second substances,
Figure BDA0002362091270000053
is the interaction between any two of Si atom and O atom (in the case where Si-Si, Si-O and O-O are present), D0Gamma is the Morse potential functionNumber of function parameters, RijIs the distance between any two atoms of Si atom, O atom and H atom, R0Cutoff radius, e is 2.7182;
by calculating the amorphous SiO2A Radial Distribution Function (RDF) of the samples, describing a Radial Distribution Function curve of the samples; and comparing the position of the first peak of the system RDF of the sample and the positions of the first valley and the second peak of the Si-O with experimental data, and verifying the correctness of the preparation method.
Step three: setting simulation parameters to simulate the diffusion process of water oxygen in amorphous silicon dioxide;
the third step comprises the following steps:
reading a data file for completing the melting process, and describing the interaction among atoms by adopting a Lennard-Jones potential function:
Figure BDA0002362091270000061
wherein u isLJ(rij) Is short-range acting force between any two atoms of Si atom, O atom and H atom, epsilon and sigma are parameters of L-J potential function, rijIs the interstitial-to-cardiac distance of any two atoms of Si atom, O atom and H atom, rcIs a cutoff radius;
remote force is expressed in coulomb force:
Figure BDA0002362091270000062
wherein E represents a long-range coulomb force, C is a long-range action parameter, qi、qjAny two atomic electric quantities of Si atom, O atom and H atom;
the action potential function parameter between any two atoms adopts Lorentz-Bertholt mixing rule, namely
Figure BDA0002362091270000063
εij＝εi 1/2εj 1/2，σi、εi、σj、εjIs a parameter of same interatomic interaction potential, sigmaij、εijIs the action potential parameter between any two atoms of Si atom, O atom and H atom.
Simulating the diffusion of water and oxygen in the amorphous silicon dioxide at 1000 ℃, 1100 ℃, 1200 ℃ and 1300 ℃ respectively;
step four: processing and analyzing data;
the fourth step comprises the following steps:
the change relation of mean-squared displacement (MSD) of the water oxygen in the amorphous silicon dioxide along with time is obtained in the third step, and the diffusion coefficient is expressed by using Einstein method as follows:
Figure BDA0002362091270000064
wherein D is the diffusion coefficient, ri(t) is the atomic position at time t, and the average value of the same type of atoms is calculated, ri(0) Is the initial time atomic position.
Example 2
A method for researching the diffusion coefficient of water vapor and oxygen in amorphous silicon dioxide comprises the following steps:
the method comprises the following steps: deriving SiO by using Material Studio software2The unit cell model is based on the construction of 8 × 8 × 15 supercell (as shown in fig. 1), and Si atoms on the surface of both ends in the Z direction are connected with O-H bonds, so that the valence state of the Si atoms is saturated. Expansion in the Z direction
Figure BDA0002362091270000071
Placing 50 water molecules and 50 oxygen molecules in the expanded region, thereby creating
Figure BDA0002362091270000072
The total number of 9082 atoms. Set up SiO2The charge of the Si atom is 1.3e, the charge of the O atom is-0.65 e, the H atom in O-H is 0.325e, the O atom in water molecule is-0.82 e, and the H atom is 0.41 e. And exporting the data file.
Step two: imitate byThe program unit is real, a periodic boundary condition is set, and the truncation radius is
Figure BDA0002362091270000073
From crystalline SiO2The steps for preparing amorphous silica are as follows: fixed H2O molecule and O2Molecular coordinates, controlling the temperature and pressure of the system, and slowly cooling from 4000K to 300K twice to obtain amorphous SiO2And (4) modeling. Firstly, under an NVT ensemble, after the system is heated to 4000K, the temperature is slowly reduced from 4000K to 300K through a 25K/ps quenching rate, then under an NPT ensemble, the temperature of a model reaches 4000K through 75ps heating, and after the model is fully melted to form a constant size, the temperature is reduced to 300K through the 25K/ps quenching rate under the NPT ensemble. The whole process adopts a time step of 0.5fs, and the pressure is kept at 1.013 multiplied by 105Pa。
The Morse function is selected to describe SiO2Interatomic interaction
Figure BDA0002362091270000074
Wherein the content of the first and second substances,
Figure BDA0002362091270000075
is the force between any two atoms of Si atom and O atom, D0Gamma is the function parameter of the Morse potential function, RijIs the distance between any two atoms of Si atom, O atom and H atom, R0Cutoff radius, e is 2.7182;
the parameters are shown in table 1:
TABLE 1 SiO2Parameters of force field
Figure BDA0002362091270000076
Calculation of amorphous SiO2The Radial Distribution Function (RDF) of a sample describes the Radial Distribution Function curve of the sample (see fig. 2). Position of first peak of system RDF of sample and Si-O first peakThe positions of the valley and the second peak are compared with the experimental data, and the correctness of the preparation method is verified.
TABLE 2 comparison of structural parameters
Structural parameters MD analog/nm Test value/nm
First peak position of O-O RDF 0.279 0.2626
First peak position of Si-Si RDF 0.243 0.3077
First peak position of Si-O RDF 0.173 0.1608
Second peak position of Si-O RDF 0.355 0.425
Step three:
reading a data file for completing the melting process, and describing the interaction among atoms by adopting a Lennard-Jones potential function:
Figure BDA0002362091270000081
wherein u isLJ(rij) Is short-range acting force between any two atoms of Si atom, O atom and H atom, epsilon and sigma are parameters of L-J potential function, rijIs the interstitial-to-cardiac distance of any two atoms of Si atom, O atom and H atom, rcIs a cutoff radius;
remote force is expressed in coulomb force:
Figure BDA0002362091270000082
wherein E represents a long-range coulomb force, C is a long-range action parameter, qi、qjAny two atomic electric quantities of Si atom, O atom and H atom;
the action potential function parameter between any two atoms adopts Lorentz-Bertholt mixing rule, namely
Figure BDA0002362091270000083
εij＝εi 1/2εj 1/2，σi、εi、σj、εjIs a parameter of same interatomic interaction potential, sigmaij、εijIs the action potential parameter between any two atoms of Si atom, O atom and H atom;
the parameters are as follows:
TABLE 3L-J force field parameters
Figure BDA0002362091270000084
Figure BDA0002362091270000091
The diffusion of water oxygen in amorphous silica was simulated at 1000 deg.C, 1100 deg.C, 1200 deg.C, 1300 deg.C, respectively.
Step four:
the mean-square displacement (MSD) of the water oxygen in the amorphous silica is obtained from step three. The diffusion coefficient is expressed using the Einstein method as:
Figure BDA0002362091270000092
wherein D is the diffusion coefficient, ri(t) is the atomic position at time t, and the average value of the same type of atoms is calculated, ri(0) Is the initial time atomic position.
Plotting MSD as a function of time is shown in FIG. 3
Curve fitting was performed, and the diffusion coefficient calculated by equation (4) was as shown in table 4,
TABLE 4 diffusion coefficient
Figure BDA0002362091270000093
A schematic diagram of the diffusion process is shown in fig. 4.
From the above analysis and fig. 3, it can be seen that the rising stage of the MSD curve of the water molecule is short, and the water molecule has completely entered SiO immediately after the start of the simulation2Internally, this is in SiO with water vapor2The solubility of inner is much higher than that of oxygen. After both molecules are completely dissolved, oxygen is in SiO2The internal diffusion coefficient of water vapor is about 1-2 orders of magnitude greater, probably due to the viscous and adsorptive nature of water vapor, while the rate of diffusion increases with increasing temperature.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims (7)

1. A method for researching the diffusion coefficient of water vapor and oxygen in amorphous silicon dioxide is characterized by comprising the following steps:
the method comprises the following steps: establishing an initial model by using Material Studio, and setting atom grouping and charge number;
step two: compiling a script by using lammps to simulate the melting process of the silicon dioxide;
step three: setting simulation parameters to simulate the diffusion process of water oxygen in amorphous silicon dioxide;
step four: and (4) processing and analyzing data.
2. The method for studying the diffusion coefficient of water vapor and oxygen in amorphous silica as claimed in claim 1, wherein said first step comprises the steps of:
α -SiO is derived by using Material Studio software2Establishing supercell, connecting Si atoms on the surfaces of two ends in the vertical upward Z direction with O-H bonds to saturate the valence state of the Si atoms, expanding the region in the Z direction, placing water molecules and oxygen molecules, establishing a diffusion initial configuration, and setting SiO2And Si atoms, O atoms, H atoms in O-H, O atoms in water molecules and H atoms in water molecules, and exporting the data file.
3. The method for studying the diffusion coefficient of water vapor and oxygen in amorphous silica according to claim 1, wherein the second step comprises the steps of:
selecting a simulation process unit, and setting a periodic boundary condition and a truncation radius;
from crystalline SiO2The steps for preparing amorphous silica are as follows: fixed H2O molecule and O2Molecular coordinates, controlling the temperature and pressure of the system, and cooling twice to obtain amorphous SiO2The model obtains a stable structure after fully relaxing the domain;
the amorphous silicon dioxide preparation process adopts Morse function to describe SiO2The interaction between the atoms is carried out,
Figure FDA0002362091260000011
wherein the content of the first and second substances,
Figure FDA0002362091260000012
is the intercropping of any two atoms of Si atom and O atomForce, D0Gamma is the function parameter of the Morse potential function, RijIs the distance between any two atoms of Si atom, O atom and H atom, R0Cutoff radius, e is 2.7182;
by calculating the amorphous SiO2A radial distribution function of the sample, describing a radial distribution function curve of the sample; the position of the first peak of the system RDF and the positions of the first and second Si-O valleys of the sample were compared to the experimental data.
4. The method for studying the diffusion coefficient of water vapor and oxygen in amorphous silica as claimed in claim 3, wherein in the second step, the simulation process unit is real, the periodic boundary condition is set, and the truncation radius is
Figure FDA0002362091260000021
5. The method for studying the diffusion coefficient of water vapor and oxygen in amorphous silica as claimed in claim 3, wherein in the second step, the diffusion coefficient of water vapor and oxygen in amorphous silica is determined from crystalline SiO2The steps for preparing amorphous silica are as follows: fixed H2O molecule and O2The molecular coordinate is that firstly, under an NVT ensemble, after the system is heated to 4000K, the temperature is reduced from 4000K to 300K through a quenching rate of 25K/ps, then under the NPT ensemble, the temperature of the model is reduced to 4000K through heating of 75ps, and after the model is fully melted to form a constant size, the temperature is reduced to 300K through the quenching rate of 25K/ps under the NPT ensemble; the whole process adopts a time step of 0.5fs, and the pressure is kept at 1.013 multiplied by 105Pa。
6. The method for studying the diffusion coefficient of water vapor and oxygen in amorphous silica as claimed in claim 1, wherein said step three comprises the steps of:
reading a data file for completing the melting process, and describing the interaction among atoms by adopting a Lennard-Jones potential function:
Figure RE-FDA0002440135890000022
wherein u isLJ(rij) Is short-range acting force between any two atoms of Si atom, O atom and H atom, epsilon and sigma are parameters of L-J potential function, rijIs the interstitial-to-cardiac distance of any two atoms of Si atom, O atom and H atom, rcIs a cutoff radius;
remote force is expressed in coulomb force:
Figure RE-FDA0002440135890000023
wherein E represents a long-range coulomb force, C is a long-range action parameter, qi、qjAny two atomic electric quantities of Si atom, O atom and H atom;
the action potential function parameter between any two atoms adopts Lorentz-Bertholt mixing rule, namely
Figure RE-FDA0002440135890000024
σi、εi、σj、εjIs a parameter of same interatomic interaction potential, sigmaij、εijIs the action potential parameter between any two atoms of Si atom, O atom and H atom; the diffusion of water oxygen in amorphous silica was simulated at 1000 deg.C, 1100 deg.C, 1200 deg.C, 1300 deg.C, respectively.
7. The method for studying the diffusion coefficient of water vapor and oxygen in amorphous silica according to claim 1, wherein said step four comprises the steps of:
the change relation of the mean square displacement of the water and the oxygen in the amorphous silicon dioxide along with the time is obtained in the third step, and the diffusion coefficient is expressed by using an Einstein method as follows:
Figure FDA0002362091260000031
wherein D is the diffusion coefficient, ri(t) is the atomic position at time t, and the average value of the same type of atoms is calculated, ri(0) Is the initial time atomic position.
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CN110097927A (en) * 2019-05-10 2019-08-06 青岛理工大学 The method for testing ionic diffusion coefficient under electric field action based on molecular dynamics

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