Prediction method for dynamic behavior of sulfur hexafluoride under external electric field based on Materials Studio

Abstract

The invention relates to the technical field of electrical equipment gas state prediction, in particular to a Materials Studio-based sulfur hexafluoride dynamic behavior prediction method under an external electric field, and the method comprises the following steps: S1) constructing a sulfur hexafluoride single molecular model, and carrying out energy and structure optimization; s2) setting an electric field parameter, and calculating a structure parameter and a spectrum curve of the sulfur hexafluoride single molecular model; s3) establishing a simulation unit with a periodic boundary condition, wherein the simulation unit comprises 128 sulfur hexafluoride molecules; s4) performing dynamic simulation on the simulation unit, calculating a mean square displacement curve and a radial distribution function, and fitting a predicted value of the diffusion coefficient; the method can predict the change of molecular structure and property of sulfur hexafluoride under the action of external electric fields with different intensities and the change of kinetic parameters, and provides reference for related experimental research of sulfur hexafluoride gas.

Description

Technical Field

[0001] The present invention relates to the technical field of design and electrical equipment insulating gas state prediction, and particularly designs a method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio. Background Art

[0002] Sulfur hexafluoride gas is still widely used in high-voltage electrical equipment due to its excellent physical properties. Under high-voltage working conditions, partial discharge is one of the common faults. Monitoring the gas state is an important task. It has a great impact on the operation of the equipment and can optimize the design of electrical equipment and improve the reliability and safety of the equipment.

[0003] At present, through the continuous study of the insulating properties of gases, the discharge phenomenon and laws of sulfur hexafluoride have been deeply explored, and an empirical formula for the breakdown voltage has been obtained, which is consistent with the experimental results within a certain range. The progress in numerical simulation has supplemented the research on the changes in the number density of electrons, the number density of ions, the electric field distribution and other phenomena during the discharge process. When studying the gas discharge mechanism and detecting the gas state, it is also of great significance to predict the changes in the properties of single molecules of sulfur hexafluoride under different external electric fields and the influence of external electric fields on the gas dynamics. They can provide data references for related research on detecting the gas state.

[0004] Therefore, a prediction method for the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio is needed to provide certain help in studying the microscopic discharge mechanism of gaseous sulfur hexafluoride and making it reasonably applied. Summary of the invention

[0005] The purpose of the present invention is to provide a prediction method for the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio. The method can use quantum mechanics methods to predict the influence of different external electric field conditions on the molecular properties of sulfur hexafluoride, and use molecular dynamics methods to predict the state changes of sulfur hexafluoride gas under different conditions, so as to provide more microscopic data and references for the utilization and state detection of insulating gas in electrical equipment and reduce experimental costs.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio, comprising the following steps:

[0007] S1) constructing a single molecule model of sulfur hexafluoride and performing energy and structure optimization;

[0008] S2) setting electric field parameters to calculate the structural parameters and spectral curve of a single molecule model of sulfur hexafluoride;

[0009] S3) establishing a simulation cell with periodic boundary conditions, including 128 sulfur hexafluoride molecules;

[0010] S4) performing a dynamic simulation on the simulation unit, calculating a mean square displacement curve and a radial distribution function, and fitting a predicted value of the diffusion coefficient;

[0011] Furthermore, in the step S1, when constructing the sulfur hexafluoride molecule, an initial molecular model of sulfur hexafluoride with a correct molecular formula is established, and based on the quantum mechanics atomic orbital linear combination method, the calculation method, basis set, and accuracy are set, and the constructed molecule is energy optimized and geometrically optimized to obtain the lowest energy configuration;

[0012] Furthermore, in step S2, electric_field is added to the input parameters to control the intensity and direction of applying different external electric fields;

[0013] Furthermore, the calculated molecular structural parameters include the total energy of the molecular ground state, the charge layout and the change of the molecular energy level, and the spectral curves include the infrared absorption spectrum and the Raman intensity spectrum;

[0014] Furthermore, in the step S3, the established dynamics simulation unit is subjected to geometric optimization and annealing simulation to obtain the lowest energy state;

[0015] Furthermore, in step S4, external electric fields of different strengths are applied to the simulation unit through script editing to simulate the working environment of sulfur hexafluoride gas in electrical equipment, and molecular dynamics calculations are performed on the lowest energy configuration under the NVT ensemble.

[0016] Furthermore, the mean square displacement curve and radial distribution function curve of the molecule are calculated from the trajectory file output by the molecular dynamics calculation, and the slope of the mean square displacement curve is calculated to obtain the change of the diffusion coefficient.

[0017] Compared with existing calculations and experiments, the present invention has the following beneficial effects: it provides a prediction method for the molecular structure and dynamic behavior of sulfur hexafluoride under an external electric field based on MaterialsStudio, which can construct a molecular model of sulfur hexafluoride, predict the changes in the molecular structure of sulfur hexafluoride molecules under the action of external electric fields of different intensities, and the changes in molecular dynamics parameters, and provide a reference for experimental research related to sulfur hexafluoride gas. By comparing the simulation with relevant literature, the initial model is closer to the experimental value; based on the advantages of software simulation calculation, the experimental cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of the method of the present invention.

[0019] Figure 2This is a model diagram of a single molecule of sulfur hexafluoride after optimization in an embodiment of the present invention.

[0020] Figure 3 It is a model diagram of a simulation unit with a periodic boundary that achieves the lowest energy configuration in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, this embodiment provides a method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio, comprising the following steps:

[0023] S1) constructing a single molecule model of sulfur hexafluoride and performing energy and structure optimization;

[0024] Establish an initial molecular model of sulfur hexafluoride with a correct molecular formula; perform energy optimization and geometry optimization on the constructed molecule, set the calculation method, basis set and accuracy, perform energy optimization and geometry optimization on the constructed molecule, and obtain the lowest energy configuration;

[0025] According to the number of atoms and molecular bonds of sulfur hexafluoride, the initial model was constructed using the sketch atom tool. The central sulfur atom was connected to the six surrounding fluorine atoms by a single bond.

[0026] The monomer model was optimized with the help of the DMOL3 module of the Materials Studio platform. The calculation parameters were set to LDA-PWC functional, DND 4.4 basis set, symmetry calculation was checked, no special treatment was performed on electrons and nuclei, and the energy threshold was set to 2.0×10 -5 Ha, the displacement threshold is set to The gradient threshold is set to The maximum number of iterations for geometry optimization is set to 500. Figure 2 The molecule has a regular octahedral structure, all SFS bond angles are 90 degrees, and the SF bond length is 1.581nm.

[0027] S2) setting electric field parameters to calculate the structural parameters and spectral curve of a single molecule model of sulfur hexafluoride;

[0028] Add electric fields with intensities of 0 a.u., 0.01 au, 0.02 au, 0.03 au, 0.04 au, and 0.05 au along the X-axis direction, and the calculation method and other parameters are the same as those in step S1, and calculate the structural parameters and spectral curves of the optimized sulfur hexafluoride single molecule model under different electric fields. The structural parameters include the total energy of the molecular ground state, the charge layout, and the change of the molecular energy level, and the spectral curves include infrared absorption spectrum, Raman intensity spectrum, and ultraviolet absorption spectrum. ;

[0029] Taking the example of adding an electric field of 0.01 au parallel to the x-axis, in order to intuitively see the changes in the structure from the three-dimensional model, first change the calculation task to geometry optimization, clear the use of symmetry option, call out the input file, add the keyword "electric_field 0.01 0 0" in the parameter part, and run the calculation.

[0030] After the calculation is completed, the calculation task of the opened molecular 3D document is changed to energy, and the calculation properties include electron density, frequency, optics, orbitals, population analysis, and Frequency (check Intensity).

[0031] Click vibrational analysis to calculate the 15 vibration modes and vibration intensities of the sulfur hexafluoride molecule, and then broaden and plot the infrared spectrum of the molecule. Click analysis-electron density, check view isosurface on input, import the surface, select display-style, change the value of the surface, and different surfaces will appear around the molecule to obtain the distribution of electrons around the molecule. Click analysis-optics and use Gaussian broadening to obtain the absorption spectrum of the molecule; click analysis-orbtics to filter the available energy levels to obtain the HOMO energy level and LUMO energy level of the molecule, check view isosurface on input, import the surface, and see the position of the energy levels. According to E g =E lumo -E homo , calculate the energy gap. Click analysis-population analysis to get the change of Mayer bond order of sulfur hexafluoride molecule under different electric field strengths. Click analysis-Raman spectrum to calculate Raman intensity spectrum, set the temperature to 298K, change the incident light wavelength to 514.5nm, reverse the horizontal and vertical axes, and get the Raman intensity spectrum of sulfur hexafluoride molecule.

[0032] After changing the size of the electric field, run the calculation again using the above method.

[0033] S3) establishing a simulation cell with periodic boundary conditions, including 128 sulfur hexafluoride molecules;

[0034] With the help of the Amorphous Cell module of the Materials Studio platform, a sulfur hexafluoride simulation cell with periodic boundary conditions was constructed based on the Monte Carlo method. The calculation task was set to Construction, containing 128 sulfur hexafluoride molecules, and the density was defined as 0.006 g / cm 3 .

[0035] With the help of Forcite module in Materials Studio, molecular dynamics calculations are performed on the simulation units, the electrostatic interaction is calculated using the Ewald method, and the van der Waals interaction is calculated using an atom-based method.

[0036] Geometry optimization parameter settings: select compassⅡ force field, set charge to Forcefield assigned, set energy threshold to 0.001 kcal / mol, and set gradient threshold to The maximum number of iterations is set to 1000.

[0037] Annealing simulation parameter settings: number of cycles is 10, initial temperature is 298K, maximum temperature is 500K, step size is 1ps, a total of 10000 steps, molecular dynamics calculations are performed under NVT ensemble, and the temperature control method is Andersen.

[0038] The optimized simulation unit is as follows Figure 3 , run a shorter molecular dynamics simulation on this structure.

[0039] S4) performing a dynamic simulation on the simulation unit, calculating a mean square displacement curve and a radial distribution function, and fitting a predicted value of the diffusion coefficient;

[0040] Molecular dynamics simulations were performed on the simulation unit with the lowest energy configuration, and different electric field parameters were set.

[0041] During the calculation process, the temperature of the simulation unit was always 298K, and the molecular dynamics calculation under the NVT ensemble was performed on the lowest energy configuration. Through script editing, different strengths of external electric fields were added, parallel to the X-axis direction, with magnitudes of 0a.u., 0.01au, 0.02au, 0.03au, 0.04au, and 0.05au, respectively. The number of optimization steps was 10,000 steps, the duration was set to 10ps, the time step was 1fs, and a frame trajectory was obtained every 0.1ps. The calculation was run to obtain a total of 100 frames of molecular dynamics simulation trajectory files.

[0042] Select the trajectory file obtained in the calculation results, click analysis-Mean square displacement, and draw the image. Click analysis-Radial distribution function, and the Cutoff is The sampling interval is Draw the image.

[0043] The diffusion coefficient of a material is defined by the following equation,

[0044]

[0045] in, represents the position vector of the atom at time t, represents the initial position of the atom, and N represents the number of molecules in the simulated system. The diffusion coefficient can better understand the changes in molecular mobility. In molecular dynamics simulation, it is obtained by solving the slope of the mean square displacement curve.

[0046] The method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio provided by the present invention can well simulate the model of sulfur hexafluoride, and the simulation results are compared with related studies to verify the correctness of the calculation model. Based on the advantages of computer simulation, the experimental cost can be reduced. The present invention predicts the changes in the structure and properties of individual molecules of sulfur hexafluoride molecules under the influence of external electric fields of different intensities by calculation, and uses the model to show the microscopic factors of the discharge and decomposition of sulfur hexafluoride under high pressure conditions. The present invention can further reveal the microscopic properties of the gas with the help of the results of the simulation unit molecular dynamics calculation, including the mean square displacement curve and the radial distribution function curve with the electric field strength, and the diffusion coefficient curve with the electric field strength.

[0047] The present invention is not limited to the examples described above. For various parameters and details, more appropriate numerical values ​​and change operation sequences can be modified according to actual experience. Without departing from the concept of the present invention, the technical solutions that can be obtained by researchers in this field through continuous practical attempts and modifications all fall within the protection scope of the present invention.

Claims

1. A prediction method for the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio. It is characterized by: The following steps are involved: S1) constructing a single molecule model of sulfur hexafluoride and performing energy and structure optimization; S2) setting electric field parameters to calculate the structural parameters and spectral curve of a single molecule model of sulfur hexafluoride; S3) establishing a simulation cell with periodic boundary conditions, including 128 sulfur hexafluoride molecules; S4) performing a dynamic simulation on the simulation unit, calculating a mean square displacement curve and a radial distribution function, and fitting a predicted value of the diffusion coefficient; In the step S2, the calculated structural parameters include the total energy of the molecular ground state, the charge layout and the molecular energy level, and the spectral curve includes the infrared absorption spectrum and the Raman intensity spectrum.

2. The method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio according to claim 1, characterized in that: In the step S1, the optimized calculation method and parameters are set to LDA-PWC functional, DND4.4 basis set, and no special treatment is performed on the electrons and cores to obtain the lowest energy structure of the molecule.

3. The method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio according to claim 1, characterized in that: In the step S2, the electric field keyword electric_field is set to control the intensity and direction of the applied external electric field.

4. The method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio according to claim 1, characterized in that: In step S3, a dynamic simulation unit is established, and the calculation task is set to Construction, the number of molecules is 128, and the density is 0.006 g / cm 3 .

5. The method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio according to claim 1, characterized in that: In step S4, external electric fields of different strengths are applied to the simulation unit through script editing, the initial configuration is optimized for 10,000 steps using conjugate gradients, the time step is 1 ps, and molecular dynamics simulation is performed in the NVT ensemble.

6. The method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio according to claim 1, characterized in that: The changes in the structure and properties of single sulfur hexafluoride molecules under the influence of external electric fields of different intensities were predicted.

7. The method for predicting the kinetic behavior of sulfur hexafluoride under an external electric field based on Materials Studio according to claim 1, characterized in that: The prediction results of sulfur hexafluoride obtained in Materials Studio, including the mean square displacement curve, the radial distribution function curve changing with the electric field strength, and the diffusion coefficient curve changing with the electric field strength.

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