Method for predicting performance of monoclinic phase vanadium dioxide based on first principle

Abstract

The invention discloses a method for predicting the performance of monoclinic-phase vanadium dioxide based on a first principle, and the method comprises the following specific steps: S1, constructing a monoclinic-phase vanadium dioxide single crystal cell structure; S2, determining an optimal algorithm; and S3, processing and analyzing a result, and obtaining the optimal algorithm for a monoclinic-phase vanadium dioxide system. According to the modification method, the screening process of new materials can be accelerated by adopting the theoretical model which is based on the first principle and high in accuracy, the number of times of experimental trial and error can be reduced through calculation and prediction, and time and cost are saved.

Description

Technical Field

[0001] The invention relates to the technical field of new material application, and more specifically to a method for predicting the performance of monoclinic vanadium dioxide based on first principles. Background Art

[0002] Smart windows can automatically adjust light transmittance and balance indoor temperature. It has always been of great significance to seek a material that can adjust solar energy according to actual needs. Some transition metal oxides show a first-order phase transition from insulator to metal at a certain temperature. For example, at a temperature close to 68°C, vanadium dioxide (VO2) undergoes a reversible semiconductor-metal phase transition, and below 68°C it transforms into a monoclinic phase (P21 / c). At high temperatures, it presents a rutile structure. The phase transition causes V 4+ The distance between them decreases, and this phase change is accompanied by the rearrangement of atoms and electrons, in which the conductivity changes by about 4 to 5 orders of magnitude, and part of the infrared light will be reflected after the phase change. Due to the above unique thermal and optical effects, vanadium dioxide has become a potential solar energy-saving material. By adjusting infrared light, vanadium dioxide film can be used as an energy-saving material for buildings, vehicles and aircraft. At the same time, if applied to smart windows, the higher phase change temperature of vanadium dioxide film material is far from the 26°C human comfort level, which limits its practical application.

[0003] The practical application of vanadium dioxide thin film materials mainly involves three issues:

[0004] ① Reduce the phase transition temperature to a temperature that can be used in practice, ② Increase the transmittance of visible light, and ③ Improve the ability to regulate solar energy. The main methods for reducing the phase transition temperature to increase light transmittance and the temperature coefficient of resistance characteristics include element doping, pressurization, granulation, etc., but experimental methods are often difficult to implement due to problems such as site, equipment, and waste of resources. The first-principles method can be used to accurately calculate and simulate the electronic structure and optical properties of the system. Accurate theoretical models can accelerate the screening process of new materials, especially in computational materials science and high-throughput computing. Candidate materials with the desired properties can be quickly identified. Computational prediction can reduce the number of experimental trial and error, saving time and material costs.

[0005] In recent years, density functional theory (DFT) has been mostly used to study the electronic structure and optical properties of monoclinic vanadium dioxide. Density functional theory may lead to self-interaction errors due to excessive electron delocalization, and thus cannot correctly describe transition metal oxides with strongly localized d electrons. The DFT+U method approximately considers the strong localized Coulomb interaction between d electrons in transition metal oxides, and successfully reduces the self-interaction errors in transition metal oxides without significantly increasing the computational cost. DFT+U is a static correction to DFT, but does not capture the frequency-dependent screening performed by delocalized electrons. The meta-GGA functional includes kinetic energy density dependence, and generally achieves better accuracy and flexibility while maintaining efficiency, but it is unknown whether the meta-GGA functional can better predict the electronic structure of the monoclinic vanadium dioxide system to improve the accuracy of theoretical simulations of the system.

[0006] The technology to be solved by this technical solution is to seek a method to accurately predict the electronic structure of the vanadium dioxide system, so as to provide theoretical guidance for the subsequent modeling and modification of monoclinic vanadium dioxide, so as to achieve the purpose of practical use of vanadium dioxide films. Summary of the invention

[0007] The present invention discloses a method for predicting the performance of monoclinic vanadium dioxide based on first principles, the main purpose of which is to overcome the above-mentioned deficiencies and shortcomings of the prior art.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A method for predicting the performance of monoclinic vanadium dioxide based on first principles, the method comprising the following specific steps:

[0010] S1, constructing a monoclinic vanadium dioxide single crystal cell structure: constructing a vanadium dioxide single crystal cell model in a first crystal structure visualization software using monoclinic vanadium dioxide single crystal file data, and then outputting the model coordinates in the form of a POSCAR file using a second crystal structure visualization software;

[0011] S2, establish the optimal algorithm: set the input file for the monoclinic vanadium dioxide single crystal cell system, and use the electronic characteristic calculation software to calculate the system using SCAN, SCAN+U (U=1.0), SCAN+U (U=3.5), r 2 SCAN, r 2 SCAN+U(U=1.0),r 2The SCAN+U (U=3.5) and LDA+U (U=3.5) methods were used to optimize the structure, and the optimized coordinate file CONTCAR was obtained. After renaming it as POSCAR file, the above 7 methods were used to perform static self-consistent calculations on the monoclinic vanadium dioxide system to generate a charge density file. According to the charge density file, the input parameters of the electronic structure calculation were set, and the electronic properties were calculated using the above 7 methods. The band structure, state density structure and band gap E were obtained by analysis and calculation. g1 、E g2 Values:

[0012] S3, result processing and analysis: The structure of the optimized monoclinic vanadium dioxide system is displayed through the second crystal structure visualization software, and the data of crystal constants and crystal volume after structural optimization are obtained; the band structure diagram and state density diagram are drawn, the band gap value is read, and the optimal calculation simulation method is determined according to the band gap value. The band gap values ​​of the monoclinic vanadium dioxide single crystal system obtained by 7 algorithms are compared with the experimental value of 0.67eV to obtain the optimal calculation method.

[0013] Furthermore, the first crystal structure visualization software is Materials Studio software, the second crystal structure visualization software is VESTA software, and the electronic structure property calculation software is VASP software.

[0014] Furthermore, the specific method of S1 is: according to the crystal constant α=90°,β=122.61°,γ=90°,use the first crystal structure visualization software to construct the single cell structure of monoclinic vanadium dioxide and generate a CIF file; then import the CIF file into the second crystal structure visualization software, export the POSCAR file, search for the pseudopotentials of vanadium and oxygen in the pseudopotential library, and use the cat command to merge them into the pseudopotential file of vanadium dioxide, which is POTCAR.

[0015] Furthermore, the specific method of S2 is:

[0016] Step 1: Use SCAN, SCAN+U (U=1.0), SCAN+U (U=3.5), r 2 SCAN, r 2 SCAN+U(U=1.0),r 2 The SCAN+U (U=3.5) and LDA+U (U=3.5) methods were used to perform first-principles structural optimization calculations on the monoclinic vanadium dioxide single crystal structure using electronic structure property software. 2SCAN is the Meta-GGA algorithm, and the parameters are set as follows: the plane wave cutoff energy is set to 500 eV, the K point is generated by the Monkhorst-Pack method, the Brillouin zone integration k-point sampling value is 4×4×4, and the convergence criteria of the single atom energy and the interatomic interaction force are 1×10 -4 eV / atom and 0.01eV, IBRION is set to 2; in the Meta-GGA algorithm, METAGGA needs to be set to SCAN or R2SCAN, and ADDGRID needs to be set to True in the INCAR file; in the +U algorithm, LDAUTYPE needs to be set to 2, LDAUPRINT needs to be set to 2; LDAUU needs to be set to 1.0 or 3.5, and LDAUJ needs to be set to 0.0; the CONTCAR file of the crystal structure with the lowest energy state after the structure optimization of the seven algorithms is calculated using the electronic structure property calculation software;

[0017] Step 2: Rename the CONTCAR file after structural optimization to POSCAR file as the input file for static self-consistent calculation. Set the input file, ICHARG to 2, ISMEAR to -5, IBRION to -2, and use the electronic structure characteristic calculation software to perform static self-consistent calculation to generate the charge density data file.

[0018] Step 3: Use the charge density data file generated by the static self-consistent calculation as one of the input files, perform electronic structure calculation, set the input parameters, set the Line mode in the KPOINTS input file when calculating the energy band diagram, and obtain the high symmetry point coordinates of monoclinic vanadium dioxide through SeeK-path or vaspkit software; in the INCAR file, ISTART is set to 1, ICHARG is set to 11, LORBIT is set to 10, ISMEAR is set to 1 for calculating the energy band structure, and ISMEAR is set to -5 for calculating the state density; use the electronic structure characteristic calculation software to calculate the system's energy band, state density and band gap E g1 、E g2 The value of .

[0019] Furthermore, the methods used in step 1, step 2 and step 3 are consistent in the process of structural optimization, self-consistent static calculation and electronic structure calculation.

[0020] Furthermore, the band gap E g From the relation (αhυ) 2 =A(hυ- g )E, where α and hυ are the absorption coefficient and photon energy, and E g1 Yes V 3d || and π * The band gap value between g2is O 2p and π * The optical band gap between .

[0021] Furthermore, the calculations performed by the electronic structure property calculation software are performed on a supercomputing cloud server, and the number of processes required for the calculation is 56.

[0022] Furthermore, the end of geometry optimization is marked by the output of the calculation results indicating “reaching the required accuracy - stop minimizing structural energy”.

[0023] It can be seen from the above description and illustration of the present invention that, compared with the prior art, the advantages of the present invention are: the modification method of the present invention adopts a theoretical model based on first principles and with high accuracy to accelerate the screening process of new materials, and can reduce the number of experimental trial and error through calculation and prediction, thus saving time and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic flow chart of the implementation method of the present invention.

[0025] Figure 2 is the band gap E of the present invention g1 and E g2 Schematic diagram of .

[0026] Figure 3 (a) Figure 3 (b) Schematic diagram of the band structure and state density calculated using the LDA+U (U=3.5) method.

[0027] Figure 4 (a) Figure 4 (b) Schematic diagram of the band structure and state density calculated using the SCAN method.

[0028] Figure 5 (a) Figure 5 (b) Schematic diagram of the band structure and state density calculated using the SCAN+U (U=1.0) method.

[0029] Figure 6 (a) Figure 6 (b) Schematic diagram of the band structure and state density calculated using the SCAN+U (U=3.5) method.

[0030] Figure 7 (a) Figure 7 (b) is to adopt r 2 Schematic diagram of the band structure and state density calculated by the SCAN method.

[0031] Figure 8 (a) Figure 8 (b) is to adopt r 2Schematic diagram of the band structure and state density calculated by the SCAN+U (U=1.0) method.

[0032] Fig. 9 (a) Fig. 9 (b) is to adopt r 2 Schematic diagram of the band structure and state density calculated by the SCAN+U (U=3.5) method. DETAILED DESCRIPTION

[0033] The specific implementation of the present invention will be further described and illustrated below with reference to the accompanying drawings.

[0034] like Figures 1 to 9 As shown, a method for predicting the performance of monoclinic vanadium dioxide based on first principles includes the following steps:

[0035] S1, constructing a monoclinic vanadium dioxide single crystal cell model: constructing a vanadium dioxide single crystal cell model in the first crystal structure visualization software using the crystal file data, and then outputting the model coordinates in the form of a POSCAR file using the second crystal structure visualization software.

[0036] S2, establish the optimal algorithm: set the input file for the monoclinic vanadium dioxide single crystal cell system, and use the electronic characteristic calculation software to calculate the system using SCAN, SCAN+U (U=1.0), SCAN+U (U=3.5), r 2 SCAN, r 2 SCAN+U(U=1.0),r 2 SCAN+U (U=3.5) and LDA+U (U=3.5) methods were used for structural optimization. Some parameter settings for structural optimization: ISIF was set to 3 and POTIM was set to 0.05. The optimized coordinate file CONTCAR file was obtained, renamed as POSCAR file, and then the above 7 methods were used to perform static self-consistent calculations on the monoclinic vanadium dioxide system to generate a charge density file; according to the charge density file, the input parameters for electronic structure calculation were set, and the electronic properties were calculated using the above 7 methods; the band structure, state density structure and band gap E were obtained by analysis and calculation. g1 、E g2 The value of .

[0037] S3, result processing and analysis: The structure of the optimized monoclinic vanadium dioxide system is displayed through the second crystal structure visualization software, and the data of crystal constants and crystal volume after the structure are obtained; the band structure diagram and state density diagram are drawn, the band gap value is read, and the optimal calculation simulation method is determined according to the band gap value.

[0038] The first crystal visualization software is Materials Studio software, the second crystal structure visualization software is VESTA software, and the electronic property calculation software is VASP (Vienna Ab-initio Simulation Package).

[0039] The sign of successful structural optimization using VASP software is that the required accuracy is achieved in the output file and the structural energy minimization is stopped. The structural optimization criteria are that the convergence of single-atom energy and the convergence of interatomic interaction force are 1×10 -4 eV / atom and 0.01eV.

[0040] The ISIF setting of 3 means that the ion position, unit cell shape and volume are optimized simultaneously. POTIM is the step size, which is used to control the moving distance of the ions during the optimization process. The smaller the value of POTIM, the smaller the step size, and the smaller the distance the ions move, which is conducive to convergence but the calculation speed will be slower;

[0041] Table 1 shows the crystal constants, volume and Helmholtz free energy of the monoclinic vanadium dioxide system calculated by different algorithms. The results show that the structural changes are within a reasonable range.

[0042] In Table 1, free energy toten is the Helmholtz free energy output by vasp during the software structure optimization process. Structural optimization is to find the atomic arrangement state with the lowest energy in the current system. Under the same convergence standard, the smaller the Helmholtz free energy, the better the convergence effect. The analysis results show that the Helmholtz free energy after structural optimization of monoclinic vanadium dioxide using the SCAN method is the lowest and the effect is the best.

[0043] Table 2 Band gap E of monoclinic vanadium dioxide system calculated by different algorithms g1 、E g2 In the energy band structure, the energy band with the highest energy filled by electrons is the valence band, where E v represents the top of the valence band, and the lowest energy band not filled with electrons is the conduction band, E c Represents the energy of the conduction band bottom, and the difference between the conduction band bottom and the valence band top is the bandgap width E g1 , E g2 is the optical band gap, which is E c The difference between E1 and E2. The results show that the band gap value E of monoclinic vanadium dioxide calculated by SCAN algorithm is g1 (0.633eV) is closest to the experimental value (0.67eV) and has the best effect.

[0044] Table 1 Crystal constants, volumes and Helmholtz free energy of monoclinic vanadium dioxide calculated by different algorithms

[0045]

[0046] Table 2 Band gap E of monoclinic vanadium dioxide calculated by different algorithms g1 、E g2 value

[0047]

[0048] The modification method of the present invention adopts a theoretical model based on first principles and with high accuracy, which can accelerate the screening process of new materials, and can reduce the number of experimental trial and error through calculation prediction, thus saving time and cost.

[0049] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial improvement of the present invention using this concept should be regarded as an infringement of the protection scope of the present invention.

Claims

1. A method for predicting the properties of monoclinic vanadium dioxide based on first principles, characterized in that: The method comprises the following specific steps: S1, constructing a monoclinic vanadium dioxide single crystal cell structure: constructing a vanadium dioxide single crystal cell model in a first crystal structure visualization software using monoclinic vanadium dioxide single crystal file data, and then outputting the model coordinates in the form of a POSCAR file using a second crystal structure visualization software; S2, establish the optimal algorithm: set the input file for the monoclinic vanadium dioxide single crystal cell system, and use the electronic characteristic calculation software to calculate the system using SCAN, SCAN+U (U=1.0), SCAN+U (U=3.5), r 2 SCAN, r 2 SCAN+U(U=1.0),r 2 The SCAN+U (U=3.5) and LDA+U (U=3.5) methods were used to optimize the structure, and the optimized coordinate file CONTCAR was obtained. After renaming it as POSCAR file, the above 7 methods were used to perform static self-consistent calculations on the monoclinic vanadium dioxide system to generate a charge density file. According to the charge density file, the input parameters of the electronic structure calculation were set, and the electronic properties were calculated using the above 7 methods. The band structure, state density structure and band gap E were obtained by analysis and calculation. g1 、E g2 Values: S3, result processing and analysis: The structure of the optimized monoclinic vanadium dioxide system is displayed through the second crystal structure visualization software, and the data of crystal constants and crystal volume after structural optimization are obtained; the band structure diagram and state density diagram are drawn, the band gap value is read, and the optimal calculation simulation method is determined according to the band gap value. The band gap values ​​of the monoclinic vanadium dioxide single crystal system obtained by 7 algorithms are compared with the experimental value of 0.67eV to obtain the optimal calculation method.

2. The method for predicting the performance of monoclinic vanadium dioxide based on first principles according to claim 1, characterized in that: The first crystal structure visualization software is Materials Studio software, the second crystal structure visualization software is VESTA software, and the electronic structure property calculation software is VASP software.

3. The method for predicting the performance of monoclinic vanadium dioxide based on first principles according to claim 1, characterized in that: The specific method of S1 is: according to the crystal constant α=90°,β=122.61°,γ=90°, use the first crystal structure visualization software to construct the monoclinic vanadium dioxide single cell structure and generate a CIF file; The CIF file is imported into the second crystal structure visualization software, and the POSCAR file is exported. The pseudopotentials of vanadium and oxygen are searched in the pseudopotential library, and the cat command is used to merge them into the pseudopotential file of vanadium dioxide, which is POTCAR.

4. The method for predicting the performance of monoclinic vanadium dioxide based on first principles according to claim 1, characterized in that: The specific method of S2 is: Step 1: Use SCAN, SCAN+U (U=1.0), SCAN+U (U=3.5), r 2 SCAN, r 2 SCAN+U(U=1.0),r 2 The SCAN+U (U=3.5) and LDA+U (U=3.5) methods were used to perform first-principles structural optimization calculations on the monoclinic vanadium dioxide single crystal structure using electronic structure property software. 2 SCAN is the Meta-GGA algorithm, and the parameters are set as follows: the plane wave cutoff energy is set to 500 eV, the K point is generated by the Monkhorst-Pack method, the Brillouin zone integration k-point sampling value is 4×4×4, and the convergence criteria of the single atom energy and the interatomic interaction force are 1×10 -4 eV / atom and 0.01eV, IBRION is set to 2; in the Meta-GGA algorithm, METAGGA needs to be set to SCAN or R2SCAN, and ADDGRID needs to be set to True in the INCAR file; in the +U algorithm, LDAUTYPE needs to be set to 2, LDAUPRINT needs to be set to 2; LDAUU needs to be set to 1.0 or 3.5, and LDAUJ needs to be set to 0.0; the CONTCAR file of the crystal structure with the lowest energy state after the structure optimization of the seven algorithms is calculated using the electronic structure property calculation software; Step 2: Rename the CONTCAR file after structural optimization to POSCAR file as the input file for static self-consistent calculation. Set the input file, ICHARG to 2, ISMEAR to -5, IBRION to -2, and use the electronic structure characteristic calculation software to perform static self-consistent calculation to generate the charge density data file. Step 3: Use the charge density data file generated by the static self-consistent calculation as one of the input files, perform electronic structure calculation, set the input parameters, set the Line mode in the KPOINTS input file when calculating the energy band diagram, and obtain the high symmetry point coordinates of monoclinic vanadium dioxide through SeeK-path or vaspkit software; in the INCAR file, ISTART is set to 1, ICHARG is set to 11, LORBIT is set to 10, ISMEAR is set to 1 for calculating the energy band structure, and ISMEAR is set to -5 for calculating the state density; use the electronic structure characteristic calculation software to calculate the system's energy band, state density and band gap E g1 、E g2 The value of .

5. The method for predicting the performance of monoclinic vanadium dioxide based on first principles according to claim 4, characterized in that: The methods used in step 1, step 2 and step 3 are consistent in the process of structural optimization, self-consistent static calculation and electronic structure calculation.

6. The method for predicting the performance of monoclinic vanadium dioxide based on first principles according to claim 4, characterized in that: The band gap E g From the relation (αhυ) 2 =A(hυ- g E) is obtained by conversion, where α and hυ are the absorption coefficient and photon energy, and E g1 Yes V 3d || and π * The band gap value between g2 is O 2p and π * The optical band gap between .

7. The method for predicting the performance of monoclinic vanadium dioxide based on first principles according to claim 1, characterized in that: The calculations performed by the electronic structure property calculation software are performed on a supercomputing cloud server, and the number of processes required for the calculation is 56.

8. The method for predicting the performance of monoclinic vanadium dioxide based on first principles according to claim 1, characterized in that: The end of geometry optimization is marked by the output of the calculation results indicating "reaching the required accuracy - stop minimizing structural energy".

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