A method for analyzing glass phase separation based on molecular dynamics simulation

Abstract

The present invention discloses a method for analyzing glass phase separation based on molecular dynamics simulation. The method comprises the following steps: constructing an amorphous initial structure model of the glass; selecting a potential function for the interaction forces between the atoms of the glass according to the types of the initial glass atoms, and performing correction processing to obtain a corrected potential function; using the corrected potential function to evolve the amorphous initial structure model into a glass structure, and collecting the atomic coordinate information of the glass structure; inputting the atomic coordinate information into the visualization software VMD to obtain a glass phase separation structure diagram, and further obtaining the microscopic structure information of the glass phase separation. Based on the molecular dynamics theory, the present invention obtains the structural phase separation information at the atomic level of the glass through the molecular dynamics simulation method, makes up for the deficiency that the experimental research cannot achieve the atomic-level structure analysis, helps to more accurately understand the glass structure phase separation behavior, and regulates the glass phase separation.

Description

Technical Field

[0001] The present invention belongs to the field of glass materials, and particularly relates to a method for analyzing glass phase separation based on molecular dynamics simulation. Background Art

[0002] Fluoride-containing oxide glass is an optical material that combines the advantages of fluoride glass and oxide glass. Its most prominent feature is that the wide adjustability of the glass composition brings about the adjustability of a series of optical properties, thus making its application range extremely wide. However, fluoride-containing oxide glass is prone to forming fluoride ion agglomeration phase separation, which seriously reduces the optical properties of fluoride-containing oxide glass. Therefore, it is crucial to control the influence of the glass composition of fluoride-containing oxide on structural phase separation.

[0003] With the progress of computer hardware and computer operation speed, and at the same time, various calculation principles and theoretical simulation technologies have gradually matured, and computational materials science has begun to take shape. Computational materials science can simulate different real experiments through a computer, and at the same time can clearly and accurately understand the microscopic structure, can simulate a large number of experiments that cannot be completed in reality, calculate the properties of different models, thus greatly saving experimental time and improving experimental efficiency. In the field of glass, researchers perform molecular dynamics simulation (MD) on glass through a computer to obtain comprehensive information on the movement trajectories of each atom in the glass system, and then use statistical methods to process these data information to obtain the influence of components on structural changes in the model system. For example, a series of parameters that can characterize the internal structure of glass, such as the radial distribution function, bond angle distribution, and coordination number distribution, are obtained. By analyzing these parameters, the component design is continuously adjusted to optimize the internal structure of the glass to meet our requirements.

[0004] According to the different effects on the glass - forming ability, the ions in fluoride - containing oxide glasses can be divided into three categories: The first category is network - forming substances. They can form glass independently and form their own unique network systems in the glass. The second category is network - modifying substances or network - modifiers. They cannot form glass independently but can change the properties of the glass. Their cations are outside the glass - structure network and are called network - modifying ions. The third category is network intermediates. Their role is between glass - forming substances and network - modifying substances. Under certain conditions, they can all form their own tetrahedral structures, connect the broken - and - shortened chains, and can increase the stability of the glass. The different proportions of glass - forming substances, network - modifiers, and network intermediates in fluoride - containing oxide glasses will directly affect the different internal structures of the glass. Existing research on glass phase separation can be carried out using detection techniques such as EM, SAXS, VLS (visible - light scattering), etc., to observe the phase - separation shape, quantity, particle - size distribution, etc. However, these tests are expensive, difficult to reserve, and have a long cycle, and finally only simple phase - separation structure morphology characteristics can be obtained (Method and system for molecular - dynamics simulation of the spatial - structure characteristics of an alumina thin film (CN114528713 A); A method for exploring the diffusion properties of each atom in a system based on molecular - dynamics simulation (CN110021380 A); A method for predicting the properties of modified asphalt based on molecular - dynamics simulation (CN 110491452 A)). Summary of the Invention

[0005] In order to overcome the deficiencies of the existing technology, the present invention provides a method for analyzing glass phase separation based on molecular - dynamics simulation. By adopting molecular - dynamics simulation, selecting the force - field function between atoms, setting the simulation parameters and method steps, the position information of each atom in the fluoride - containing oxide glass system can be directly obtained. Through visualization software, the phase - separation characteristics of the glass structure can be accurately obtained, thus providing guidance for regulating phase separation.

[0006] Using the molecular - dynamics simulation technology, the present invention can not only obtain the morphological characteristics of the phase - separation structure of fluoride - containing oxide glasses, but also obtain the structural parameters at the atomic level, which is beneficial to further analyzing the phase - separation structure characteristics.

[0007] The object of the present invention is achieved by at least one of the following technical solutions.

[0008] A method for analyzing glass phase separation based on molecular - dynamics simulation, comprising the following steps:

[0009] S1. Construct an amorphous initial - structure model of the glass through PACKMOL software. According to the experimentally measured glass density, determine the side length of the amorphous initial - structure model, and export the coordinate file of the initial glass atoms;

[0010] S2. Select the potential function of the interaction force between the atoms of the glass according to the types of the initial glass atoms in step S1, and perform correction processing to obtain the corrected potential function;

[0011] S3. Use the corrected potential function obtained in step S2 through molecular dynamics simulation to evolve the amorphous initial structure model in step S1 into a glass structure, and collect the atomic coordinate information of the glass structure;

[0012] S4. Input the atomic coordinate information collected in step S3 into the visualization software VMD to obtain the glass phase separation structure diagram, and further obtain the microscopic structure information of the glass phase separation.

[0013] Further, in step S1, the glass refers to a fluorine-containing oxide glass, including fluorophosphate glass, fluorosilicate glass or fluoroborate glass.

[0014] Further, in step S2, the types of glass atoms include network formers, network modifiers and network intermediates.

[0015] Further, the network formers include P, Si and B; the network modifiers include alkali metals and alkaline earth metal elements; the network intermediates include Al, Ti, Pb and Ga.

[0016] Further, in step S2, the selected potential function is the Buckingham potential function, and the expression of the potential function is:

[0017]

[0018] Among them, r represents the distance between atom i and atom j, q i and q j respectively represent the charges of atom i and atom j, and A ij , B ij , C ij are the Buckingham potential parameters between atom i and atom j.

[0019] Further, in step S2, the correction processing is to perform correction processing on the Buckingham potential, and the form of the correction formula is as follows:

[0020]

[0021] Among them, D ij , n ij , E ij are the correction parameters between atom i and atom j, and the correction parameters are obtained when the first derivative and the second derivative of the correction function and the potential function are continuous.

[0022] Further, in step S3, evolving the amorphous initial structure model in step S1 into a glass structure involves first relaxing it at 5000K for 500 ps, then decreasing the temperature from 5000K to 300K at a rate of 0.2K / step with a step size of 2 fs, and relaxing it for 20 ps after reaching 300K.

[0023] Further, in step S4, the microstructure information refers to the structure characterization parameters describing the phase separation characteristics of the glass, including the coordination number and the structure cluster ratio.

[0024] Further, the coordination number refers to the number of other fluoride ions in the nearest neighbor atomic layer of a fluoride ion, which is calculated by formula (3):

[0025]

[0026] where ρ is the density of the glass, g(r) is the radial distribution function of fluorine-fluorine, and r 0 is the minimum value after the first peak of the radial distribution function.

[0027] Further, the structure cluster ratio characterizes the aggregation degree of fluoride ions in the glass structure and is calculated by formula (4):

[0028]

[0029] where CN F-F is the coordination number of fluorine-fluorine, r c is the cut-off radius used when calculating CN F-F ; N F represents the number of fluorine atoms in the volume V box of the amorphous initial structure model of the glass.

[0030] Compared with the prior art, the present invention has the following advantages and effects:

[0031] The present invention provides a method for analyzing glass phase separation based on molecular dynamics simulation. This method can obtain the atomic position information in fluoride-containing oxide glass by molecular dynamics simulation, clearly see the glass structure at the atomic level through visualization software, and obtain structural information such as coordination number and structure cluster ratio by calculation. The structural phase separation information of fluoride-containing oxide glass can be obtained without actual experiments throughout the process, greatly reducing the experimental cost. Based on this information, the components can be improved, which can be used to control the phase separation of fluoride-containing oxide glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flowchart of a method for analyzing glass phase separation based on molecular dynamics simulation in an embodiment of the present invention.

[0033] Figure 2The planar graph after processing the output structure data with a component of 20Al in the embodiments of the present invention 2 O 3 % in the visualization software VMD.

[0034] Figure 3 The planar graph after processing the output structure data with a component of 25Al in the embodiments of the present invention 2 O 3 % in the visualization software VMD.

[0035] Figure 4 The planar graph after processing the output structure data with a component of 30Al in the embodiments of the present invention 2 O 3 % in the visualization software VMD.

[0036] Figure 5 The planar graph after processing the output structure data with a component of 35Al in the embodiments of the present invention 2 O 3 % in the visualization software VMD. Detailed implementation manners

[0037] The following will further illustrate the specific implementation of the present invention in conjunction with the drawings and embodiments, but the scope of protection required by the present invention is not limited thereto.

[0038] Embodiment:

[0039] In one embodiment, a method for analyzing phase separation of glass based on molecular dynamics simulation is used to regulate the phase separation of fluoro-phosphate glass in the P 2 O 5 -Al 2 O 3 -CaO-CaF 2 -YbF 3 system, as Figure 1 shown, including the following steps:

[0040] S1. Construct an amorphous initial structure model of the glass through PACKMOL software, determine the side length of the amorphous initial structure model according to the experimentally measured glass density, and export the coordinate file of the initial glass atoms;

[0041] The glass refers to fluorine-containing oxide glass, including fluoro-phosphate glass, fluoro-silicate glass or fluoro-borate glass.

[0042] In one embodiment, the glass under study is fluoro-phosphate glass, and the glass composition is 40P 2 O 5 -xAl 2 O 3 -(40-x)CaO-15CaF2 -5YbF 3 (x = 20, 25, 30, 35 mol%), the information of the amorphous initial structure model is shown in Table 1. The amorphous initial structure model of the glass was constructed by PACKMOL software and the structure file was exported.

[0043] Table 1 Information on the construction of the glass model

[0044]

[0045] S2. Select the potential function of the interaction force between the atoms of the glass according to the types of the initial glass atoms in step S1, and perform a correction process to obtain the corrected potential function.

[0046] The types of glass atoms include network formers, network modifiers, and network intermediates.

[0047] The network formers include P, Si, and B; the network modifiers include alkali metals and alkaline earth metal elements; the network intermediates include Al, Ti, Pb, and Ga.

[0048] The selected potential function is the Buckingham potential function, and the expression of the potential function is:

[0049]

[0050] Among them, r represents the distance between atom i and atom j, q i and q j represent the charges of atom i and atom j respectively, and A ij , B ij , C ij are the Buckingham potential parameters between atom i and atom j, and these parameters are generally cited from relevant literature and databases.

[0051] The correction process is to correct the Buckingham potential. Due to the existence of the exponential form in the Buckingham potential formula, when two atoms are infinitely close to each other, the interatomic force will be infinitely small, which violates the physical law; therefore, a correction formula needs to be added to correct the Buckingham potential, and the form of the correction formula is as follows:

[0052]

[0053] Among them, D ij , n ij , E ij are the correction parameters between atom i and atom j, and the correction parameters are obtained when the first derivative and the second derivative of the correction function and the potential function are continuous.

[0054] The potential function of the interaction force between atoms in the modified glass is shown in Table 2. The determined modified Buckingham potential function is written into the in file for executing the Lammps running command.

[0055] Table 2 Potential function of the interaction force between atoms in the modified glass

[0056]

[0057]

[0058] S3. Using the modified potential function obtained in step S2 through molecular dynamics simulation, evolve the amorphous initial structure model in step S1 into a glass structure, and collect the atomic coordinate information of the glass structure;

[0059] In one embodiment, molecular dynamics simulation is performed on the constructed glass model through the molecular dynamics software Lammps. First, the energy of the glass initial structure is minimized, and then the glass system is relaxed for 500 ps at 5000 K under the NVT ensemble to remove the internal stress of the system and improve the accuracy of the simulation. Then, the glass model is cooled from 5000 K to 300 K at a rate of 0.2 K / step, and after reaching 300 K, it is relaxed for another 20 ps. The NVT ensemble (canonical ensemble) is used throughout the cooling process, and the time step is 2 fs. Finally, the atomic coordinate information of the fluorophosphate glass at equilibrium is output every 100 steps under the NVE ensemble (microcanonical ensemble), and the total number of steps is 20000 steps.

[0060] S4. Input the atomic coordinate information collected in step S3 into the visualization software VMD to obtain the glass phase separation structure diagram, and further obtain the microscopic structure information of the glass phase separation;

[0061] The microscopic structure information refers to the structural characterization parameters describing the glass phase separation characteristics, including the coordination number and the structure cluster ratio.

[0062] The coordination number refers to the number of other fluoride ions in the nearest neighbor atomic layer of a fluoride ion, which is calculated by formula (3):

[0063]

[0064] where ρ is the density of the glass, g(r) is the radial distribution function of fluorine-fluorine, and r 0 is the minimum value after the first peak of the radial distribution function.

[0065] The structure cluster ratio characterizes the aggregation degree of fluoride ions in the glass structure and is calculated by formula (4):

[0066]

[0067] Among them, CN F-F is the coordination number of fluorine-fluorine, and r c is the intercept radius used when calculating CN F-F ; N F represents the number of fluorine atoms within the volume V box of the amorphous initial structure model of the glass.

[0068] In one embodiment, by opening the glass structure file output by Lammps with the visualization software VMD, the glass phase separation structure can be clearly seen, as shown in Figure 2 , Figure 3 , Figure 4 , Figure 5 . Import the glass structure file output by Lammps into a python script to calculate the coordination number between F-F and the structure cluster rate, as shown in Table 3.

[0069] Table 3 Coordination number between F-F and structure cluster rate.

[0070]

[0071]

[0072] Through visualization software and calculations, it can be obtained that as the network intermediate Al 3+ continuously replaces the network modifier Ca 2 + , the phase separation region of the fluorophosphate glass continuously decreases, and the coordination number of F-F and the structure cluster rate continuously decrease, realizing the regulation of the phase separation of the fluorophosphate glass.

[0073] The above embodiments are only the implementation manners of the present invention, and are only used to explain the present invention, rather than limiting the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for analyzing glass phase separation based on molecular dynamics simulation, characterized in that, it includes the following steps: S1. Construct an amorphous initial structure model of the glass through PACKMOL software. According to the glass density measured by experiments, determine the side length of the amorphous initial structure model, and export the coordinate file of the initial glass atoms; S2. Select the potential function of the interaction force between the atoms of the glass according to the types of the initial glass atoms in step S1, and perform correction processing to obtain the corrected potential function; the selected potential function is the Buckingham potential function, and the expression of the potential function is: Among them, r represents the distance between atoms i and atom j . q i and q j respectively represent the charges of atoms i and atom j . A ij , B ij , C ij are the Buckingham potential parameters between atoms i and atom j . S3. Use the corrected potential function obtained in step S2 through molecular dynamics simulation to evolve the amorphous initial structure model in step S1 into a glass structure, and collect the atomic coordinate information of the glass structure; S4. Input the atomic coordinate information collected in step S3 into visualization software to obtain a glass phase separation structure diagram, and further obtain the microscopic structure information of the glass phase separation; the microscopic structure information refers to the structural characterization parameters describing the characteristics of the glass phase separation, including the coordination number and the structure cluster ratio; the coordination number refers to the number of other fluoride ions in the nearest neighbor atomic layer of a fluoride ion, which is calculated by formula (3): Among them, ρ is the density of the glass, g ( r ) is the radial distribution function of fluorine-fluorine, r 0 is the minimum value after the first peak of the radial distribution function; The structure cluster ratio characterizes the aggregation degree of fluoride ions in the glass structure, and is calculated by formula (4): Among them, CN F-F is the coordination number of fluorine-fluorine, r c is the intercept radius used in the calculation of CN F-F ; N F represents the volume of the amorphous initial structure model of the glass V box and the number of fluorine atoms inside.

2. The method for analyzing glass phase separation based on molecular dynamics simulation according to claim 1, characterized in that, in step S1, the glass refers to fluoride-containing oxide glass, including fluorophosphate glass, fluorosilicate glass or fluoroborate glass.

3. The method for analyzing glass phase separation based on molecular dynamics simulation according to claim 1, characterized in that, in step S2, the types of glass atoms include network formers, network modifiers and network intermediates.

4. The method for analyzing glass phase separation based on molecular dynamics simulation according to claim 3, characterized in that, the network formers include P, Si and B; the network modifiers include alkali metals and alkaline earth metal elements; the network intermediates include Al, Ti, Pb and Ga.

5. The method for analyzing glass phase separation based on molecular dynamics simulation according to claim 1, characterized in that, in step S2, the correction processing is to correct the Buckingham potential, and the form of the correction formula is as follows: Among them, D ij , n ij , E ij are the correction parameters between atoms i and atom j , and the correction parameters are obtained when the first-order and second-order derivatives of the correction function and the potential function are continuous.

6. The method for analyzing glass phase separation based on molecular dynamics simulation according to claim 1, characterized in that, in step S3, evolving the amorphous initial structure model in step S1 into a glass structure is first relaxed at 5000K for 500ps, then decreased from 5000K to 300K, the decreasing rate is 0.2K / step, the step size is 2fs, and after reaching 300K, it is relaxed for 20ps.

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