Molecular dynamics simulation method for electron-induced gas desorption

Abstract

The invention discloses a molecular dynamics simulation method for electron-induced gas desorption, and belongs to the technical field of molecular simulation. The method comprises the following steps: firstly, constructing an aluminum oxide molecular model, and then simulating adsorption equilibrium of hydrogen on the surface of aluminum oxide at different temperatures and air pressures by adopting a giant regular Monte Carlo method to obtain a stable adsorption configuration; then, based on the configuration, an electron force field is adopted to introduce explicit electron particles to simulate electron beam bombardment, and an electron-induced gas desorption kinetic process is simulated under a molecular dynamics framework; and finally, performing quantitative analysis on the desorption product. Through full-atom molecular dynamics simulation, coherent research from gas adsorption to electron-induced desorption is realized, the limitation that related experimental measurement is difficult and a micromechanism is difficult to reveal under a high-voltage condition is overcome, and an effective simulation tool is provided for deeply understanding a physical mechanism of dielectric surface gas desorption-induced discharge.

Description

Technical Field

[0001] This invention relates to the field of molecular simulation technology, and more specifically to a molecular dynamics simulation method for electron-induced gas desorption. Background Technology

[0002] In high-voltage vacuum electronic devices, gas adsorption and desorption on dielectric surfaces are key factors inducing early discharge and leading to device failure. During device manufacturing and operation, dielectric materials such as alumina adsorb a large number of gas molecules. When high voltage is applied or a local strong electric field is present, mechanisms such as Joule heating and electron bombardment provide energy for the adsorbed gas, triggering its rapid desorption. The instantaneously released gas forms a high-density gas cloud locally, significantly reducing insulation strength. Desorbed gas molecules are easily ionized under an electric field, ultimately inducing surface flashover or breakdown.

[0003] Currently, experiments measuring gas adsorption / desorption usually need to be carried out under high vacuum conditions. Under high pressure conditions, although the electron-induced effect still exists, experimental measurements often face problems such as large signal interference, poor repeatability, and difficulty in accurately detecting low-energy electrons, resulting in unreliable measurement results and an inability to accurately reveal the microscopic mechanism of electron-induced desorption.

[0004] Therefore, there is an urgent need for a technical means to reliably study the gas adsorption and electron-induced desorption processes at the microscopic scale under complex conditions such as high pressure and low-energy electrons, in order to gain a deeper understanding of the physical mechanism of gas desorption-induced discharge on dielectric surfaces. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a molecular dynamics simulation method for electron-induced gas desorption.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This application provides a molecular dynamics simulation method for electron-induced gas desorption, comprising the following steps:

[0008] Step S1. Construct an alumina molecular model;

[0009] Step S2. Based on the alumina molecular model, simulate the adsorption process of gas molecules on its surface to obtain a stable adsorption model;

[0010] Step S3. Based on a stable adsorption model, an explicit electronic force field is used to simulate the electron beam-induced gas desorption process.

[0011] Furthermore, step S1 includes:

[0012] Choose a standard alumina crystal structure;

[0013] The crystal structure is expanded to construct a three-dimensional model;

[0014] Export the constructed model as a data file readable by molecular dynamics simulation software.

[0015] Furthermore, step S2 includes:

[0016] Construct a simulation box containing an alumina substrate and a vapor phase region;

[0017] Gas molecules are randomly generated in the gas phase region;

[0018] The adsorption equilibrium of gas molecules on the alumina surface was simulated using the giant canonical Monte Carlo method under different preset temperature and / or preset pressure conditions.

[0019] The stable configuration that reaches adsorption equilibrium is derived as a stable adsorption model.

[0020] Furthermore, in step S2, the gas molecules are hydrogen; and / or

[0021] The adsorption process of gas molecules on its surface is simulated using the Lennard-Jones force field to describe the van der Waals interactions between atoms.

[0022] Furthermore, in step S2, the preset temperature is selected from at least one of 300K, 400K, and 500K; and / or

[0023] The preset air pressure is selected from 1 bar, 0.1 bar, 0.01 bar, 0.001 bar, 0.0001 bar, and 10 bar. -6 At least one of the following: bar.

[0024] Furthermore, step S3 includes:

[0025] Energy relaxation was applied to the stable adsorption model to bring the system to a steady state;

[0026] A simulated electron beam is introduced into the system, in which electrons are configured as explicit particles with mass and initial velocity.

[0027] The interaction between electrons and atomic systems is described using an electronic force field to simulate the kinetics of gas desorption induced by electron bombardment.

[0028] Furthermore, the electronic force field is an electronic force field in which electrons are described by deformable Gaussian wave packets; and / or

[0029] An effective nuclear potential is used for the atoms in alumina.

[0030] Furthermore, the energy of the electron beam is adjustable; and / or

[0031] The electron beam is introduced into a predefined cylindrical spatial region at a set density.

[0032] Furthermore, it also includes step S4:

[0033] Analyze the simulation results of the desorption process to obtain the evolution of the types and quantities of desorbed particles over time and / or the desorption yield.

[0034] Furthermore, step S4 includes:

[0035] Import the simulated trajectory file into visualization software for process observation and data analysis.

[0036] Compared with the prior art, this application has the following beneficial effects:

[0037] This application provides a molecular dynamics simulation method for electron-induced gas desorption, comprising the following steps: Step S1. Constructing an alumina molecular model; Step S2. Based on the alumina molecular model, simulating the adsorption process of gas molecules on its surface to obtain a stable adsorption model; Step S3. Based on the stable adsorption model, using an explicit electronic force field to simulate the electron beam-induced gas desorption process; By constructing a gas adsorption model on the alumina surface and using an explicit electronic force field to simulate the electron-induced desorption process, the entire process of gas adsorption to electron bombardment desorption under high pressure conditions can be realistically and controllably reproduced, overcoming the limitations of traditional experimental methods in high-pressure, low-energy electronic environments where measurements are unreliable and it is difficult to capture microscopic mechanisms. This provides an effective simulation research method for deeply revealing the microscopic mechanism of gas desorption-induced discharge on dielectric surfaces. Attached Figure Description

[0038] Figure 1 This is a schematic flowchart of the electron-induced gas desorption simulation method for alumina surface provided in this embodiment of the invention.

[0039] Figure 2 This is a crystal structure diagram of Al2O3 provided in an embodiment of the present invention.

[0040] Figure 3 This invention provides an embodiment of the method for measuring different air pressures (1 bar, 10 bar) at 300 K. -3 bar, 10 -6 (bar) diagram of the adsorption state of hydrogen on the surface of alumina.

[0041] Figure 4 This is a schematic diagram simulating the electron-induced gas desorption process provided in an embodiment of the present invention.

[0042] Figure 5This is a schematic diagram showing the evolution of the number of different particle types over time during electron-induced desorption at 300K, 1 bar pressure, and 20 eV incident electron energy, provided by an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Furthermore, in this invention, an element referred to as fixed to or disposed on another element may be directly disposed on the other element, or there may be an intermediate element. When an element is considered to be connected to another element, it may be directly connected to the other element, or there may be an intermediate element present simultaneously. The terms vertical, horizontal, left, right, and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0045] Example 1

[0046] This invention utilizes molecular dynamics simulation technology to progressively study the entire process from substrate modeling and gas adsorption simulation to electron-induced desorption. The specific implementation can be completed using molecular dynamics simulation platforms such as LAMMPS and GROMACS, and mainly includes the following four core steps:

[0047] Step S1. Construct an alumina molecular model.

[0048] This invention uses Al2O3 as the research object. First, it is necessary to construct its atomic-scale model. In practice, a standard Al2O3 crystal structure file is selected from a publicly available crystal structure database. Then, according to the size requirements of the actual simulation system, the crystal structure is expanded in the X, Y, and Z directions to construct a three-dimensional supercell model with periodic boundary conditions to ensure the separation of surface effects from bulk properties. After the modeling is completed, the model is exported as a data format file that can be recognized by the simulation software, such as the Al2O3.data file. This file should contain the coordinates, element types, lattice vectors, and bonding information of all atoms.

[0049] Step S2. Based on the alumina molecular model, simulate the adsorption process of gas molecules on its surface to obtain a stable adsorption model.

[0050] The goal of this step is to obtain stable adsorption configurations of hydrogen molecules on the alumina surface under different temperatures and preset pressures.

[0051] First, the simulation system is constructed and parameters are initialized. The alumina model prepared in the first step is placed at the bottom of the box, and the height in the Z direction is increased to leave enough space for the gas phase region. The spatial dimension is set to three dimensions, and periodic boundary conditions are applied in all directions. The simulation unit system is selected as the metal unit system, in which the energy unit is electron volt, the distance unit is Å, and the time unit is ps.

[0052] Secondly, a certain number of H2 molecules are randomly generated within the gas phase region of the simulation chamber to simulate the gas phase environment. The non-bonded interactions between atoms are described using the Lennard-Jones potential function, with an appropriate cutoff radius set, such as 10 Å.

[0053] Next, a grand canonical Monte Carlo (GCMC) simulation was performed to study the adsorption behavior. The temperature was controlled using an NVT ensemble, and the system was relaxed to a set background temperature (300 K, 400 K, or 500 K) through a temperature coupling method. In the GCMC simulation, a chemical potential corresponding to the target gas pressure was set; the background gas pressure could be selected as 1 bar, 10 bar, or 10 bar. -3 bar or 10 -6 During the simulation, the system randomly attempts to insert, delete, or move hydrogen molecules until adsorption equilibrium is reached. Finally, the atomic configuration file of this state is exported as the initial structure for subsequent desorption simulations. This process allows for a systematic study of the relationship between adsorption capacity and environmental conditions, and the results can be observed using visualization software, such as... Figure 3 As shown, the differences in adsorption states at different pressures under 300K are illustrated.

[0054] Step S3. Based on a stable adsorption model, an explicit electronic force field is used to simulate the electron beam-induced gas desorption process.

[0055] This step starts with the stable adsorption model obtained in the second step and simulates the desorption kinetics process induced by electron beam bombardment.

[0056] First, the simulation environment is reset and the system energy is relaxed. The simulation unit system is switched to real units, where the time step is usually on the order of fs, which is more suitable for simulating fast processes involving electrons. The energy of the alumina system with adsorbed hydrogen is minimized to eliminate local unreasonable configurations. Then, a molecular dynamics simulation is run for a period of time in the NVE microcanonical ensemble, for example, 500,000 steps, to allow the total energy of the system to fully relax and reach a steady state.

[0057] Secondly, a force field suitable for electron-atom coupling simulation is configured; the core is the use of an electronic force field. Within this force field framework, each valence electron participating in the reaction is explicitly described as an independent particle with mass and coordinates, and its electron cloud shape is characterized by a Gaussian wave packet of variable width, thus naturally describing the polarization, delocalization, and charge transfer processes of electrons. For aluminum and oxygen atoms in alumina, an effective nuclear potential is used to describe the equivalent interaction between their inner-shell electrons and the atomic nucleus, so as to significantly reduce the number of electrons and improve computational efficiency. The van der Waals interactions between all atoms in the system are still handled by the Lennard-Jones potential function.

[0058] Then, a simulated electron beam is constructed and introduced into the system; an electron incident region is defined above the simulated region, such as a cylindrical space with a radius of 2.5 Å and a height of 3000 Å; within this region, a large number of electron particles, such as 3000, are randomly generated to simulate a high-density electron beam; each electron particle is assigned an initial velocity vector corresponding to a preset incident energy, such as 20 eV, with the direction perpendicular to the alumina surface.

[0059] Finally, molecular dynamics simulations of electron-atom coupling were performed; the equations of motion for both electrons and atoms were integrated simultaneously within the NVE ensemble; the simulations showed how electrons convert kinetic energy into the system's internal energy through inelastic scattering with adsorbed hydrogen molecules and alumina surface atoms, inducing a series of events such as vibrational excitation, ionization, and dissociation of hydrogen molecules, ultimately leading to the desorption of gas molecules from the surface. This dynamic process can be observed using visualization tools, as illustrated in the diagram below. Figure 4 As shown.

[0060] Step S4: Import the simulated trajectory file into visualization software for process observation and data analysis; after the simulation calculation is completed, analyze the output trajectory data to extract physical mechanisms and quantitative information.

[0061] The trajectory files containing all particle positions and velocities saved during the simulation, such as LAMMPS dump files, are imported into professional scientific visualization and analysis software, such as OVITO or VMD. This software allows for dynamic playback of the entire electron bombardment and gas desorption process, providing a direct visual observation of the phenomena. Figure 4 As shown; furthermore, by performing programmatic analysis on the trajectory data, the evolution of different desorption products over simulation time can be quantitatively statistically analyzed; such as Figure 5 As shown, curves showing the changes in the number of hydrogen ions, hydrogen atoms, hydrogen molecules, E molecules, and hydrogen anions over time can be obtained. Based on these data, key physical quantities, such as the yield of electron-induced desorption and the branching ratio of different products, can be calculated, thereby revealing the reaction pathway and kinetic mechanism of electron-induced gas desorption at the microscopic level.

[0062] Example 2

[0063] The technical solution of this application will be further described in detail below with reference to the accompanying drawings:

[0064] First, see Figure 1 The implementation process of the method of this invention mainly includes four core stages:

[0065] Construction of the alumina substrate model.

[0066] Simulation of gas adsorption under different conditions.

[0067] Electron beam-induced gas desorption kinetics simulation.

[0068] Visualization and quantitative analysis of simulation results.

[0069] The following is a detailed explanation of each stage.

[0070] Phase 1: Construction of the alumina-based molecular model

[0071] This phase aims to create an atomic-level alumina substrate model for simulation, with the corresponding crystal structure as follows: Figure 2 As shown.

[0072] During implementation, the standard stoichiometric α-Al₂O₃ crystal structure file is first obtained from authoritative crystallography databases (such as ICSD and MaterialsProject). Then, according to the size requirements of the simulation system, the crystal unit cell is expanded in the X, Y, and Z spatial directions using materials simulation software (such as VESTA and Atomsk) or scripts. For example, a three-dimensional periodic supercell model with a surface size of approximately 1.5 nm × 1.5 nm and a thickness of approximately 1.5 nm can be constructed to ensure sufficient surface representativeness and reduce the interaction of periodic mirror images. Finally, the constructed model is exported in a data format recognizable by the molecular dynamics software LAMMPS to generate an Al₂O₃.data file. This file precisely contains the coordinates, element types, lattice constants, and chemical bond information of all aluminum and oxygen atoms, providing an accurate initial configuration for subsequent simulations.

[0073] Phase 2: Simulation of hydrogen adsorption equilibrium on the alumina surface

[0074] The goal of this stage is to obtain a stable adsorption distribution of hydrogen molecules on the alumina surface under different ambient temperatures and pressures. Typical results are shown below. Figure 3 As shown.

[0075] The specific implementation steps are as follows:

[0076] In the LAMMPS software, the Al2O3.data file exported in the first stage is read in and the height of the box in the z-direction is expanded to set the gas phase region. The simulation units are set to metal units, the spatial dimension is three-dimensional, and periodic boundary conditions are applied in all directions. In the gas phase space above the box, a predetermined number of hydrogen molecules are randomly generated using the create_atoms command to initialize the gas phase environment.

[0077] The van der Waals interactions between all atoms (Al, O, H) were described using Lennard-Jones potential functions, and literature-verified potential parameters were set for each atom pair. First, the entire system, including the substrate and gas phase, was minimized and fully relaxed under the NVT ensemble, and the system temperature was controlled at a set value, such as 300K, 400K, or 500K, using a Nosé-Hoover hot bath.

[0078] In the relaxed system, the grand canonical Monte Carlo method was applied to simulate the adsorption equilibrium. The target gas phase pressure (e.g., 1 bar, 10 bar) was set using the `fix gcmc` command. -3 bar and 10 -6 The chemical potential corresponding to bar, etc.; the GCMC simulation will randomly perform insertion, deletion and movement operations on hydrogen molecules under constant temperature and volume conditions until the system reaches chemical potential equilibrium, that is, the adsorption and desorption rates are dynamically equal; this process simulates the interaction between gas molecules and material surfaces under real environment.

[0079] After equilibrium is reached, export the final atomic configuration file; import this file into the visualization analysis software OVITO to observe, for example... Figure 3 The adsorption state is shown; through the analysis software's custom analysis script, it is possible to statistically calculate different pressures (e.g., 1 bar, 10 bar, etc.). -3 bar, 10 -6 The adsorption surface density of hydrogen on the alumina surface at bar (bar) visually demonstrates the change in adsorption capacity with pressure (see...). Figure 3 (a, 3b, 3c)

[0080] Phase 3: Kinetic simulation of electron-induced gas desorption

[0081] This stage uses the stable adsorption model obtained in the second stage as the initial structure to simulate the dynamic process of gas desorption induced by electron beam bombardment. A schematic diagram is shown below. Figure 4 As shown.

[0082] Switching the simulation unit system to the real unit system, where the fs-level time step is more suitable for describing rapid processes involving electrons, and then performing energy minimization to eliminate local stress after reading the stable adsorption model, followed by running molecular dynamics simulations (e.g., 500,000 steps) in the NVE (microcanonical) ensemble for a period of time to allow the total energy of the system to fully relax under isolated conditions and reach a stable state, thus preparing for electron injection.

[0083] By using the eff potential function in LAMMPS, the valence electrons participating in the reaction are treated as explicit, massive particles. Each electron is described by a deformable Gaussian wave packet, the width of which is a dynamic variable, thus enabling self-consistent simulation of quantum effects such as electron cloud polarization and charge transfer. To balance computational accuracy and efficiency, an effective nuclear potential is used for aluminum and oxygen atoms, explicitly describing only their valence and conduction band electrons.

[0084] Above the simulation region, a cylindrical electron source region is defined (e.g., radius 0.25 nm, height 300 nm); a large number of electron particles (e.g., three thousand) are randomly generated within this region, either once or in batches, using the LAMMPS command; by assigning a specific initial velocity to each electron particle (its magnitude is derived from a preset electron beam energy, such as 20 eV), a high-density electron beam incident vertically is simulated bombarding the material surface, such as... Figure 4 As shown.

[0085] Molecular dynamics simulations were run in the NVE ensemble to solve the equations of motion for electrons and atomic nuclei. Electrons transferred energy to the adsorbed hydrogen molecules and alumina lattice through inelastic scattering, triggering a series of complex events such as vibrational excitation, dissociation, and ionization of hydrogen molecules, ultimately leading to the desorption of various products from the surface.

[0086] Phase 4: Visualization and Mechanism Analysis of Simulation Results

[0087] This stage analyzes the trajectory data output from the third stage simulation to extract quantitative information and reveal microscopic mechanisms. Typical analysis results are as follows: Figure 5 As shown.

[0088] Import the trajectory files saved during the simulation (such as LAMMPS dump files) into OVITO software; through the software's playback function, the entire evolution process of electron bombardment and gas desorption can be observed dynamically and intuitively (e.g., Figure 4 The instantaneous state shown); quantitative statistics can be performed on trajectory data by writing or using OVITO's built-in analysis routines; for example, different types of desorption products (such as H) can be analyzed. + Ions, H atoms, H - The evolution of the quantity of ions (and H2 molecules) over simulation time; Figure 5 This illustrates a typical evolution curve: in the initial stage, high-energy electrons directly cause hydrogen ionization, producing a large amount of H₂. + and electrons; over time, some H + H atoms combine with base electrons to form H atoms, and an electron-rich environment may also encourage H atoms to capture electrons to form H₂. - Meanwhile, some undissociated H2 molecules undergo physical desorption after gaining sufficient kinetic energy. Based on this data, key physical quantities such as electron-induced desorption yield and branching ratio of each product can be further calculated, thereby revealing the complete dynamic chain at the atomic and electronic scale.

[0089] This invention constructs a complete simulation framework from atomic modeling to mechanistic analysis through the four closely integrated and progressively advancing implementation stages described above. In particular, by introducing an explicit electronic force field, this method successfully achieves a realistic simulation of electron-induced surface processes at the classical molecular dynamics scale, providing an innovative theoretical research platform for the design and failure analysis of high-voltage insulating materials.

[0090] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0091] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A molecular dynamics simulation method for electron-induced gas desorption, characterized in that, Includes the following steps: Step S1. Construct an alumina molecular model; Step S2. Based on the alumina molecular model, simulate the adsorption process of gas molecules on its surface to obtain a stable adsorption model; Step S3. Based on a stable adsorption model, an explicit electronic force field is used to simulate the electron beam-induced gas desorption process.

2. The method according to claim 1, characterized in that, Step S1 includes: Choose a standard alumina crystal structure; The crystal structure is expanded to construct a three-dimensional model; Export the constructed model as a data file readable by molecular dynamics simulation software.

3. The method according to claim 1, characterized in that, Step S2 includes: Construct a simulation box containing an alumina substrate and a vapor phase region; Gas molecules are randomly generated in the gas phase region; The adsorption equilibrium of gas molecules on the alumina surface was simulated using the giant canonical Monte Carlo method under different preset temperature and / or preset pressure conditions. The stable configuration that reaches adsorption equilibrium is derived as a stable adsorption model.

4. The method according to claim 3, characterized in that, In step S2, the gas molecules are hydrogen; and / or The adsorption process of gas molecules on its surface is simulated using the Lennard-Jones force field to describe the van der Waals interactions between atoms.

5. The method according to claim 3, characterized in that, In step S2, the preset temperature is selected from at least one of 300K, 400K, and 500K; and / or The preset air pressure is selected from 1 bar, 0.1 bar, 0.01 bar, 0.001 bar, 0.0001 bar, and 10 bar. -6 At least one of the following: bar.

6. The method according to claim 1, characterized in that, Step S3 includes: Energy relaxation was applied to the stable adsorption model to bring the system to a steady state; A simulated electron beam is introduced into the system, in which electrons are configured as explicit particles with mass and initial velocity. The interaction between electrons and atomic systems is described using an electronic force field to simulate the kinetics of gas desorption induced by electron bombardment.

7. The method according to claim 6, characterized in that, Electrons in the said electronic force field are described by deformable Gaussian wave packets; and / or An effective nuclear potential is used for the atoms in alumina.

8. The method according to claim 6, characterized in that, The energy of the electron beam is adjustable; and / or The electron beam is introduced into a predefined cylindrical spatial region at a set density.

9. The method according to any one of claims 1 to 8, characterized in that, It also includes step S4: Analyze the simulation results of the desorption process to obtain the evolution of the types and quantities of desorbed particles over time and / or the desorption yield.

10. The method according to claim 9, characterized in that, Step S4 includes: Import the simulated trajectory file into visualization software for process observation and data analysis.

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