Calculation method for optical property of infrared band in thermal control material

Abstract

The invention discloses a method for calculating the optical property of an infrared band in a thermal control material, and belongs to the field of spacecraft thermal control material design. The method aims at solving the problems that most of existing mainstream calculation thoughts focus on related calculation in a sunlight band, and calculation research on optical properties of materials in a middle-infrared band is relatively few. The method comprises the following steps: establishing a unit cell model, and performing high-precision optimization on the structure model through a step-by-step optimization method; calculating a second-order force constant matrix, a BORN effective charge, a dielectric constant tensor, a third-order force constant matrix and a tri-phonon scattering rate; determining an optical phonon vibration mode of the center of the Brillouin region with infrared activity; and calculating the dielectric function of the material according to the Lorentz oscillator model, and further calculating the refractive index and the extinction coefficient of the material. According to the method, the calculation precision and efficiency of the optical property of the infrared band in infrared optics in the thermal control material are remarkably improved, a reliable theoretical basis is provided for research and development of new materials, the experiment cost can be effectively reduced, and the research and development period is shortened.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal control material design for spacecraft, and specifically relates to a method for calculating the mid-infrared band optical properties of thermal control materials. Background Art

[0002] As a special functional material, the thermal control coating for aerospace can achieve precise temperature control by adjusting the infrared thermal radiation characteristics of the spacecraft, and is widely used on the surfaces of spacecraft such as satellites, manned spaceflight, and space stations. Traditional thermal control materials include materials such as ZnO, TiO 2 , ZrO 2 , SiO 2 , etc., and new types of intelligent thermal control materials include materials such as VO 2 , WO x , La 1-x Sr x MnO 3 , etc. The intrinsic infrared optical properties of these thermal control materials have an important impact on the performance of their thermal control coatings. Therefore, the research and development of new thermal control materials with excellent infrared optical properties is of great significance for meeting the thermal control requirements of spacecraft.

[0003] The core parameters for the design of new thermal control materials include their absorptivity in the solar light band and emissivity in the infrared light band, which can reflect the regulation ability of the material in space thermal radiation management. The intrinsic optical constants (refractive index n and extinction coefficient k) of the material are the basis for calculating its optical properties, and are crucial for the development of new thermal control materials and the design of thermal control coatings. Usually, the complex dielectric function (ε) of the new material can be obtained through theoretical calculation, and then the optical constants of the material can be obtained by using the relationship between the complex refractive index and the complex dielectric function of the material. However, the current mainstream optical property calculation methods mainly focus on the analysis of the electronic behavior of the material: based on Fermi's golden rule, by describing the photon absorption caused by electron transitions, the imaginary part of the dielectric function is calculated; and then through the Kramers-Kronig transformation relationship, the real part of the dielectric function is further obtained. Since the light absorption process caused by electron transitions mainly focuses on the solar light band with higher energy and shorter wavelength, this method cannot accurately calculate the optical properties of thermal control materials in the mid-infrared band with larger wavelengths.

[0004] Limited by the wavelength limitations of traditional calculation methods, it is impossible to accurately obtain the optical properties in the mid-infrared band when designing new thermal control materials, resulting in difficulty in accurately predicting the thermal control performance of materials, and further affecting the accuracy and reliability of the thermal control function of spacecraft. Therefore, there is an urgent need to develop a calculation method for the optical properties of thermal control materials in the mid-infrared band to accurately describe the infrared thermal radiation characteristics of thermal control materials, provide a theoretical basis and technical support for the research and development of new optical materials in the mid-infrared band, and strongly promote the design of thermal control materials and the development of thermal control coatings. Summary of the Invention

[0005] Compared with the calculation of optical properties only targeting electronic behavior, the present invention provides a calculation method for the mid-infrared optical properties of dielectric materials based on phonon behavior. For the mid-infrared optical properties of thermal control materials, based on the density functional theory, phonon spectra are calculated using software packages such as VASP, Phonopy, THIRDORDER.PY, and ShengBTE, and the dielectric function in the mid-infrared band is fitted according to the Lorentz oscillator model.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The calculation method for the optical properties of dielectric materials in the mid-infrared band includes the following steps:

[0008] Step 1: Establish a unit cell model and perform high-precision optimization on the unit cell model through a step-by-step optimization method;

[0009] Step 2: Calculate the second-order force constant matrix, BORN effective charge, dielectric constant tensor, third-order force constant matrix, and three-phonon scattering rate;

[0010] Step 3: Determine the optical phonon vibration modes at the center of the Brillouin zone with infrared activity;

[0011] Step 4: Calculate the dielectric function of the material according to the Lorentz oscillator model; use the relationship between the complex refractive index of the material and the dielectric function to calculate the refractive index and extinction coefficient of the material; thus, the calculation is completed.

[0012] Further defined, the thermal control material is an inorganic material, such as silicon dioxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), vanadium dioxide (VO 2 ), lanthanum strontium manganite (La 1-x Sr x MnO 3 , LSMO), silicon nitride (Si 3 N 4 ), silicon carbide (SiC), calcium fluoride (CaF 2 ) and other inorganic materials.

[0013] Further defined, in step one, the unit cell model is established by retrieving unit cell information through Materials Studio software or The Materials Project crystal website, and exporting the unit cell model cif file.

[0014] Further defined, in step one, the high-precision optimization of the unit cell model by the step-by-step optimization method is achieved through the following steps:

[0015] Step 1.1: Convert the cif file into a POSCAR file through VESTA software; generate a POTCAR file according to the unit cell elements and functionals; generate KPOINTS and INCAR files through the K-point and cut-off energy ENCUT convergence test;

[0016] Step 1.2: Set the force convergence parameter in INCAR so that IBRION = 1, ISIF = 3, EDIFFG = -1E-2, and perform the first structural optimization; then copy the calculated CONTCAR as POSCAR, set EDIFFG to -1E-3, and perform the second optimization;

[0017] Step 1.3: Further improve the force convergence accuracy so that ISIF = 2, EDIFFG = -1E-4, and copy the CONTCAR calculated in the previous step as POSCAR to perform the third optimization; complete the high-precision optimization.

[0018] Further defined, in step two, calculate the second-order force constant matrix, Born effective charge, and dielectric constant tensor through the following steps: Call the Phonopy software package, set IBRION = 8, LEPSILON =.TRUE. in INCAR, and perform the calculation using density functional perturbation theory (DFPT); extract the high-frequency dielectric constant tensor and Born effective charge from the calculated OUTCAR, and generate a BORN file, and extract and generate the FORCE_CONSTANTS second-order force constant matrix file from the calculated vasprun.xml file.

[0019] Further limitation: In step 2, the third-order force constant matrix is calculated through the following steps: Call the THIRDORDER.PY software package, appropriately expand the primitive unit cell, and consider an appropriate number of nearest neighbors as the cut-off value. Use the finite displacement method to generate several POSCAR-00* files; copy the POSCAR-00* files to the job-00* folder and rename them to POSCAR. Prepare the POTCAR, INCAR, and KPOINTS files. Set NSW = 0 and IBRION = -1 in the INCAR, and perform single-point energy calculations in sequence; after all calculations are completed, collect and generate the FORCE_CONSTANTS_3RD third-order force constant matrix file from the vasprun.xml file obtained from each calculation.

[0020] Further limitation: In step 2, the three-phonon scattering rate is calculated through the following steps: Generate a CONTROL file according to the element type, lattice information, etc., and place it in the same folder as the FORCE_CONSTANTS_2ND second-order force constant matrix file calculated in step 2.1 and the FORCE_CONSTANTS_3RD third-order force constant matrix file calculated in step 2.2; call the ShengBTE software package for calculation; extract the three-phonon scattering rate from the calculated BTE.w_anharmonic file.

[0021] Further limitation: Determining the optical phonon vibration mode at the center of the Brillouin zone with infrared activity is carried out according to the following steps:

[0022] Step 3.1: Set the tolerance to 0.001, generate a symm.conf configuration file, and execute the command phonopy --readfc --dim="111" symm.conf, where phonopy represents calling the phonopy program, --readfc represents reading the force constant, --dim="111" represents setting the supercell size of the crystal, "111" means only considering the initial primitive cell, and symm.conf represents the symm.conf configuration file, which is used to assist phonon calculations; extract the frequency and irreducible representation of the optical phonon vibration mode at the Gamma point (0, 0, 0) from the calculation result irreps.yaml file.

[0023] Step 3.2: Upload the crystal cif file on the Bilbao Crystallographic Server website (https: / / www.cryst.ehu.es / rep / sam.html) to obtain the irreducible representation of the infrared-active optical phonon mode of the crystal; compare the results of step 3.1 to obtain the frequency corresponding to the infrared-active optical phonon mode.

[0024] Step 3.3: Generate the band.conf configuration file according to the high-symmetry point path of the unit cell, and execute the command phonopy -c POSCAR -p -s band.conf, where phonopy means calling the phonopy program, -c POSCAR means reading the crystal structure file POSCAR, -p means calculating the phonon band structure map, and -s band.conf means specifying the band.conf file for calculation; after the calculation is completed, the phonon spectrum map is obtained;

[0025] Step 3.4: Considering the longitudinal-transverse (LO-TO) splitting of the infrared-active modes, enable the non-analytical term correction, set NAC =.TRUE., and specify the non-analytical term correction direction Q_DIRECTION to generate a new symm.conf configuration file and band.conf configuration file; respectively execute the commands in Steps 3.1 and 3.3 to obtain the frequencies of the optical phonon vibration modes and the phonon spectrum map at the corrected Gamma point (0, 0, 0);

[0026] Step 3.5: Compare the frequencies of the optical phonon vibration modes and the phonon spectrum map before and after considering the LO-TO splitting. At the Gamma point, the one with the higher frequency after the LO-TO splitting is the LO frequency, and the lower one is the TO frequency.

[0027] Furthermore, it is specified that in Step 4, the dielectric function ε(ω) of the material is calculated through the Lorentz oscillator model shown by the following formula:

[0028]

[0029] where ε(ω) is the dielectric function, ε ∞ is the high-frequency dielectric constant, ω j is the resonance frequency, j represents all infrared-active modes, ω is the frequency in the mid-infrared band, S j is the oscillator strength of the j-th phonon mode, γ j is the three-phonon scattering rate of the j-th phonon mode, and LO and TO respectively represent the longitudinal and transverse optical phonon modes;

[0030] Calculate the refractive index n(ω) and extinction coefficient k(ω) of the material through the following relationship:

[0031]

[0032] where n(ω) is the refractive index, k(ω) is the extinction coefficient, ε 1 (ω) is the real part of the dielectric function, and ε 2 (ω) is the imaginary part of the dielectric function.

[0033] The present invention utilizes the influence of phonon action on the dielectric function in the infrared band to accurately describe the optical properties of thermal control materials in this band. By calculating the phonon modes with infrared activity and using the Lorentz oscillator model to describe them, the present invention effectively captures the contribution of phonon modes to the dielectric function of the material. The Lorentz oscillator model provides an accurate frequency dependence for the calculation of the dielectric function by simulating the dynamic behavior of the interaction between phonon modes and photons, thereby enhancing the prediction ability of the optical response of materials in the mid-infrared band. The method of the present invention provides a more refined theoretical tool for optimizing infrared optical performance and designing new materials.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention provides a new method for calculating the optical properties of thermal control materials in the mid-infrared band, which can more comprehensively consider the optical characteristics of materials in this band and make up for the deficiencies of the prior art in the application of the mid-infrared band. Based on density functional theory, using software packages such as VASP, Phonopy, THIRDORDER.PY, and ShengBTE, and fitting the dielectric function through the Lorentz oscillator model, considering the influence of phonon action on optical properties, significantly improving the calculation accuracy and efficiency of the optical properties of thermal control materials in the mid-infrared band.

[0036] The method of the present invention not only provides a reliable theoretical basis for the research and development of new materials in the mid-infrared band, promoting the development of technologies such as intelligent thermal control; but also reduces the consumption of experimental materials, thereby reducing costs and shortening the research and development cycle, strongly promoting the development of thermal control technology and having broad application prospects.

[0037] In order to further understand the features and technical content of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the accompanying drawings are only for reference and illustration purposes and are not used to limit the present invention. Description of the Drawings

[0038] Figure 1 It is the calculation flowchart of Embodiment 1 of the present invention. Detailed Embodiments

[0039] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and at the same time do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention. Detailed Embodiment 1:

[0041] This embodiment provides a method for calculating the optical properties of a thermal control material in the mid-infrared band. This calculation uses software packages such as VASP, Phonopy, THIRDORDER.PY, and ShengBTE, and fits the dielectric function according to the Lorentz oscillator model, as Figure 1 shown. Specifically, calculate the dielectric function of α-SiO 2 in the mid-infrared band. The specific steps are as follows:

[0042] Step 1. Establish a unit cell model and perform high-precision optimization on the structural model;

[0043] The specific content of Step 1 is as follows:

[0044] Step 1.1: Retrieve the unit cell information of α-SiO 2 through the The Materials Project crystal website (https: / / legacy.materialsproject.org) and export the cif file;

[0045] Step 1.2: Use VESTA software to convert the cif file into a POSCAR file; adopt the PBE (Perdew-Burke-Ernzerhof) exchange-correlation functional to generate the POTCAR file; set the K-points to a Gamma k-point network of 9×9×5, and set the cut-off energy ENCUT to 520 eV to generate the KPOINTS and INCAR files;

[0046] Step 1.3: Use the VASP software package, set IBRION = 1, ISIF = 3, and EDIFFG = -1E-2 in INCAR to perform the first structural optimization; then copy the calculated CONTCAR as POSCAR, set EDIFFG to -1E-3, and perform the second optimization;

[0047] Step 1.4: Further improve the force convergence accuracy, make ISIF = 2, EDIFFG = -1E-4, and copy the CONTCAR obtained in the previous step as POSCAR to perform the third optimization; complete the high-precision optimization.

[0048] Step 2: Calculate the second-order force constant matrix, BORN effective charge, dielectric constant tensor, third-order force constant matrix, and three-phonon scattering rate;

[0049] The specific content of Step 2 is as follows:

[0050] Step 2.1: Call the Phonopy software package, set IBRION = 8 and LEPSILON =.TRUE. in INCAR, and perform calculations using density functional perturbation theory (DFPT); extract the high-frequency dielectric constant tensor and Born effective charges from the calculated OUTCAR and generate a BORN file, and extract and generate a second-order force constant matrix file FORCE_CONSTANTS from the calculated vasprun.xml file;

[0051] Step 2.2: Call the THIRDORDER.PY software package, expand the primitive unit cell by 2×2×2, select the 5th nearest neighbor atom as the cut-off value, and generate 264 POSCAR-00* files using the finite displacement method; copy the POSCAR-00* files to the job-00* folder and rename them to POSCAR, prepare the POTCAR, INCAR, and KPOINTS files, set NSW = 0 and IBRION = -1 in INCAR, and perform single-point energy calculations in sequence; after all calculations are completed, collect and generate a third-order force constant matrix file FORCE_CONSTANTS_3RD from the vasprun.xml file obtained from each calculation;

[0052] Step 2.3: Generate a CONTROL file according to the element type and lattice information, and place it in the same folder as the second-order force constant matrix file FORCE_CONSTANTS_2ND calculated in Step 2.1 and the third-order force constant matrix file FORCE_CONSTANTS_3RD calculated in Step 2.2; call the ShengBTE software package for calculation; extract the three-phonon scattering rate from the calculated BTE.w_anharmonic file.

[0053] Step 3: Determine the optical phonon vibration modes at the center of the Brillouin zone with infrared activity;

[0054] The specific steps of Step 3 are as follows:

[0055] Step 3.1: Set the tolerance to 0.001, generate a symm.conf configuration file, and execute the command phonopy --readfc --dim = "222" symm.conf, where phonopy represents calling the phonopy program, --readfc represents reading the force constants, --dim = "222" represents setting the supercell size of the crystal to 2×2×2 times that of the primitive unit cell, and symm.conf represents the symm.conf configuration file, which is used to assist phonon calculations; extract the frequencies and irreducible representations of the optical phonon vibration modes at the Gamma point (0,0,0) from the calculation result irreps.yaml file;

[0056] Step 3.2: Upload the α-SiO 2 crystal cif file to the Bilbao Crystallographic Server website (https: / / www.cryst.ehu.es / rep / sam.html) to obtain the irreducible representation of the infrared-active optical phonon modes of the crystal; comparing with the results of Step 3.1, the frequencies corresponding to the infrared-active optical phonon modes can be obtained;

[0057] Step 3.3: Generate a band.conf configuration file according to the high-symmetry point path of the unit cell, and execute the command phonopy -c POSCAR -p -s band.conf, where phonopy means calling the phonopy program, -c POSCAR means reading the crystal structure file POSCAR, -p means calculating the phonon band structure map, and -s band.conf means specifying the band.conf file for calculation; after the calculation is completed, a phonon spectrum map is obtained;

[0058] Step 3.4: Considering the longitudinal-transverse (LO-TO) splitting of the infrared-active modes, enable the non-analytical term correction, set NAC =.TRUE., and specify the non-analytical term correction direction Q_DIRECTION to generate a new symm.conf configuration file and band.conf configuration file; respectively execute the commands in Steps 3.1 and 3.3 to obtain the frequencies of the optical phonon vibration modes and the phonon spectrum map at the Gamma point (0, 0, 0) after correction;

[0059] Step 3.5: Compare the frequencies and phonon spectrum maps of the optical phonon vibration modes before and after considering the LO-TO splitting. At the Gamma point, the one with the higher frequency after the LO-TO splitting is the LO frequency, and the lower one is the TO frequency.

[0060] Step 4: Calculate the dielectric function of the material according to the Lorentz oscillator model; use the relationship between the complex refractive index and the dielectric function of the material to calculate the refractive index and extinction coefficient of the material;

[0061] The specific content of Step 4 is as follows:

[0062] Calculate the dielectric function ε(ω) of the material through the Lorentz oscillator model shown by the following formula:

[0063]

[0064] where ε(ω) is the dielectric function, ε ∞ is the high-frequency dielectric constant, ω jis the resonant frequency, j represents all infrared active modes, ω is the frequency in the mid-infrared band, S j is the oscillator strength of the j-th phonon mode, γ j is the three-phonon scattering rate of the j-th phonon mode. LO and TO represent longitudinal and transverse optical phonon modes respectively; the refractive index n(ω) and extinction coefficient k(ω) of the material are calculated through the following relational expressions:

[0065]

[0066] wherein, n(ω) is the refractive index, k(ω) is the extinction coefficient, ε 1 (ω) is the real part of the dielectric function, ε 2 (ω) is the imaginary part of the dielectric function.

[0067] The method of this embodiment significantly improves the calculation accuracy and efficiency.

[0068] The above is only a preferred embodiment of a calculation method for the optical properties of a thermal control material in the mid-infrared band. The protection scope of a calculation method for the optical properties of a thermal control material in the mid-infrared band is not limited to the above embodiments. Any technical solutions falling within this concept belong to the protection scope of the present invention. It should be noted that for those skilled in the art, several improvements and variations made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for calculating the optical properties of thermal control materials in the mid-infrared band, characterized in that: The following steps are involved: Step 1: Establish a unit cell model and optimize the unit cell model with high precision through a step-by-step optimization method; Step 2: Calculate the second-order force constant matrix, BORN effective charge, dielectric constant tensor, third-order force constant matrix, and three-phonon scattering rate; Step 3, determine the optical phonon vibration mode at the center of the infrared-active Brillouin zone; Step 4: Calculate the dielectric function of the material based on the Lorentz oscillator model; the calculation is completed.

2. The method according to claim 1, characterized in that: The thermal control material is an inorganic material.

3. The method according to claim 1, characterized in that: In step 1, the unit cell model is established by retrieving the unit cell information through MaterialsStudio software or The Materials Project crystal website, and exporting the unit cell model cif file.

4. The method according to claim 1, characterized in that: In step 1, high-precision optimization is achieved through the following steps: Step 1.1: Use VESTA software to convert the cif file into a POSCAR file, then generate a POTCAR file, and then generate KPOINTS and INCAR files through the K point and cutoff energy ENCUT convergence test; Step 1.2: Set the force convergence parameters in INCAR so that IBRION = 1, ISIF = 3, EDIFFG = -1E-2, perform the first structural optimization, then copy the calculated CONTCAR to POSCAR, set EDIFFG to -1E-3, and perform the second optimization; Step 1.3: Further improve the force convergence accuracy so that ISIF=2, EDIFFG=-1E-4, and copy the CONTCAR calculated in the previous step to POSCAR for the third optimization; complete the high-precision optimization.

5. The method according to claim 4, characterized in that: Generate a POTCAR file based on the unit cell elements and functionals.

6. The method according to claim 4, characterized in that: In step 2, the second-order force constant matrix, BORN effective charge, and dielectric constant tensor are calculated by the following steps: call the Phonopy software package, set IBRION=8, LEPSILON=.TRUE. in INCAR, and use density functional perturbation theory (DFPT) for calculation; extract the high-frequency dielectric constant tensor and BORN effective charge in the calculated OUTCAR, and generate a BORN file; extract and generate the FORCE_CONSTANTS second-order force constant matrix file from the calculated vasprun.xml file.

7. The method according to claim 1, characterized in that: In step 2, the third-order force constant matrix is ​​calculated by the following steps: call the THIRDORDER.PY software package, expand the primitive cell appropriately, consider an appropriate number of neighboring atoms (nearest neighbors) as the cutoff value, and use the finite displacement method to generate several POSCAR-00* files; copy the POSCAR-00* file to the job-00* folder and rename it to POSCAR, prepare POTCAR, INCAR, and KPOINTS files, set NSW=0 and IBRION=-1 in INCAR, and perform single-point energy calculations in turn; after all calculations are completed, collect and generate the FORCE_CONSTANTS_3RD third-order force constant matrix file from the vasprun.xml file obtained in each calculation.

8. The method according to claim 1, characterized in that: In step 2, the three-phonon scattering rate is calculated by the following steps: Generate a CONTROL file based on the element type, lattice information, etc., and place it in the same folder as the FORCE_CONSTANTS_2ND second-order force constant matrix file and the FORCE_CONSTANTS_3RD third-order force constant matrix file; The ShengBTE software package is called for calculation; the three-phonon scattering rate is extracted from the calculated BTE.w_anharmonic file.

9. The method according to claim 1, characterized in that: In step 3, the optical phonon vibration mode at the center of the infrared-active Brillouin zone is determined by the following steps: Step 3.1: Set the tolerance to 0.001, generate the symm.conf configuration file, and execute the command phonopy --readfc --dim="111"symm.conf, where phonopy means calling the phonopy program, --readfc means reading the force constant, --dim="111" means setting the supercell size of the crystal, "111" means only considering the initial primitive cell, and symm.conf means the symm.conf configuration file, which is used to assist phonon calculations; extract the frequency and irreducible representation of the optical phonon vibration mode at the Gamma point (0,0,0) from the calculation result irreps.yaml file; Step 3.2: Upload the crystal cif file on the Bilbao Crystallographic Server website to obtain the irreducible representation of the infrared active optical phonon mode of the crystal; compare the results of step 3.1 to obtain the frequency corresponding to the infrared active optical phonon mode; Step 3.3: Generate the band.conf configuration file according to the high symmetry point path of the unit cell, and execute the command phonopy-cPOSCAR-ps band.conf, where phonopy means calling the phonopy program, -c POSCAR means reading the crystal structure file POSCAR, -p means calculating the phonon band structure spectrum, and -s band.conf means specifying the band.conf file for calculation; After the calculation is completed, the phonon spectrum is obtained; Step 3.4: Consider the infrared active mode longitudinal wave-transverse wave (LO-TO) splitting, enable non-analytical correction, set NAC = TRUE, and specify the non-analytical correction direction Q_DIRECTION, and generate new symm.conf configuration files and band.conf configuration files; Execute the commands of steps 3.1 and 3.3 respectively to obtain the frequency and phonon spectrum of the optical phonon vibration mode at the corrected Gamma point (0,0,0); Step 3.5: Compare the frequencies and phonon spectra of the optical phonon vibration modes before and after LO-TO splitting. At the Gamma point, the higher frequency after LO-TO splitting is the LO frequency, and the lower frequency is the TO frequency.

10. The method according to claim 1, characterized in that: In step 4, the dielectric function ε(ω) of the material is calculated by the following formula: Where ε(ω) is the dielectric function, ε ∞ is the high frequency dielectric constant, ω j is the resonant frequency, j represents all infrared active modes, ω is the frequency in the mid-infrared band, S j is the oscillator strength of the jth phonon mode, γ j is the three-phonon scattering rate of the jth phonon mode, LO and TO represent the longitudinal and transverse optical phonon modes, respectively; The refractive index n(ω) and extinction coefficient k(ω) of the material are calculated by the following relationship: Among them, n(ω) is the refractive index, k(ω) is the extinction coefficient, ε1(ω) is the real part of the dielectric function, and ε2(ω) is the imaginary part of the dielectric function.

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