High-performance layered nitride thermoelectric material screening method and system

Abstract

The invention discloses a high-performance layered nitride thermoelectric material screening method and system. The method comprises the following steps: acquiring a series of crystal structures of initial layered nitride; carrying out magnetic test on the material by utilizing first principle calculation, and selecting a non-magnetic material; carrying out structure optimization on the non-magnetic material, carrying out static calculation and electron energy band structure calculation after calculation convergence, and selecting a material with a band gap range of 0.1-3 eV and high energy band structure degeneracy; calculating partial charge density of the material, and judging whether two-dimensional electron gas exists or not, namely, alternate occurrence of a conductive layer and an insulating layer; stability judgment: carrying out phonon spectrum and molecular dynamics simulation calculation on the material, and selecting the material with phonon spectrum without imaginary frequency and stable dynamics; the heat transport performance of the material is calculated, the lattice heat conductivity and Green Ehson parameters are obtained, and the material with high non-harmony is found; and finally, carrying out electric transport calculation to obtain the ZT value of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric material screening, and in particular to a method and system for screening high-performance layered nitride thermoelectric materials. Background Art

[0002] Thermoelectric materials are materials that can directly convert thermal energy (such as solar energy, waste heat, etc.) into electrical energy. If thermoelectric devices with low cost and high thermoelectric conversion efficiency can be developed, it will be of great help in alleviating the current energy crisis and environmental pollution. Thermoelectric performance is usually expressed by the dimensionless thermoelectric figure of merit (ZT). ZT = S 2 T / ( + ), it can be seen from the formula that due to the nature of the material itself, it is impossible to improve the Seebeck coefficient and electrical conductivity at the same time. The only way to achieve the optimal thermoelectric figure of merit is to appropriately increase the power factor or significantly reduce the thermal conductivity.

[0003] Since the thermoelectric conversion efficiency of traditional materials is too low, this has promoted the development of thermoelectric materials towards more advanced and complex combinations. Layered compounds often have electronic properties superior to those of traditional metals and semiconductors. Transition metal (TM) oxides have attracted widespread attention due to their unconventional carrier transport properties. The most representative example is the two-dimensional electron gas (2DEG) in the SrTiO3 heterointerface. The destruction of the interface degeneracy allows the material to form a conduction band channel in the 2DEG layer, which plays an important role in its high electron mobility, superconductivity, ferromagnetism and Seebeck coefficient, showing enhanced electron mobility and improved conductivity; and people have conducted in-depth research on layered TM oxides composed of alternating conductive layers composed of TM ions and insulating barrier layers, and discovered unique electromagnetic properties; and KCoO2-type layered composite nitrides show strong band anisotropy, large effective mass and better electrical transport properties. However, the excellent 2DEG performance only appears in very thin regions near the heterostructure interface. It might be more interesting if this 2DEG was contained at high density in bulk materials, where the 2DEG properties would appear throughout the bulk phase, but to the best of our knowledge, such materials are rare.

[0004] A layered ternary transition metal nitride semiconductor AMN2, where A and M are alkaline earth metal atoms and transition metal atoms, has been identified as a promising thermoelectric material due to its unique two-dimensional electronic structure embedded in a bulk crystal structure. It adopts a tetragonal KCoO2-type layered crystal structure with a natural superlattice consisting of MN conducting layers and AN insulating layers along the c-axis, and two-dimensional electronic structures and anisotropic transport properties can be expected. So far, the number of known AMN2 compounds is small compared to layered complex metal oxides and chalcogenides, and there may still be unknown AMN2 layered complex metal nitrides that may exhibit new physical properties.

[0005] Therefore, an efficient screening method is urgently needed to identify potential thermoelectric materials in AMN2. Summary of the invention

[0006] Purpose of the invention: In order to overcome the above shortcomings, the purpose of the present invention is to provide a method and system for screening high-performance layered nitride thermoelectric materials.

[0007] In order to solve the above technical problems, the present invention provides a method for screening high-performance layered nitride thermoelectric materials, comprising: Step S1: obtaining a layered nitride material according to the initial crystal structure of the material, and then performing a magnetic test on the layered nitride material using first-principles calculations to obtain a non-magnetic material; Step S2: Optimizing the structure of the non-magnetic material, and then performing static calculation and electronic band structure calculation to screen out the preset band gap material; Step S3: Calculate the preset charge density of the preset bandgap material to determine whether there is a two-dimensional electron gas. If so, execute the next step. If not, exclude the material without a two-dimensional electron gas. Step S4: perform phonon spectrum and molecular dynamics calculations to screen out materials with no imaginary frequency and stable dynamics; Step S5: Perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, and then obtain a target layered nitride material that meets preset requirements.

[0008] In one aspect, in step S1, the method comprises the following steps: Step S11: optimizing the layered nitride material using first principle calculation software to obtain spatial structure information data of the layered nitride material, and then constructing force field information data and preset grid density data for each spatial structure contained in the layered nitride material; Step S12: In the spatial structure information data of the layered nitride material, the electronic wave function is processed using the projected plane wave and the electronic structure is calculated using the PBE-GGA exchange-correlation functional; Step S13: setting a preset spin polarization parameter according to the spatial structure information data in the layered nitride material, so as to screen out non-magnetic layered nitride materials.

[0009] In one aspect, it is characterized in that, in step S2, the method comprises the following steps: Step S21: increasing the grid density of the non-magnetic material to perform structural relaxation; Step S22: After the structure converges, a self-consistent calculation is performed to generate a charge density file of the material; Step S23: using the projected augmented wave method and the generalized gradient approximation as the exchange-correlation function to calculate the electronic band structure of the material, and then screening out materials within a preset band gap range.

[0010] In one aspect, in step S3, the method comprises the following steps: Step S31: calculating the partial charge density of the valence band top and the conduction band bottom of the material in the preset band gap range, and determining whether the charge density of the conduction band bottom of the material appears in the atomic layer formed by the transition metal-nitrogen bond; Step S32: If yes, it is determined that the material in the preset bandgap range has two-dimensional electron gas; if no, it is determined that the material in the preset bandgap range does not have two-dimensional electron gas, and the material in the preset bandgap range is excluded.

[0011] In one aspect, in step S4, the method comprises the following steps: Step S41: calculating the phonon dispersion curve of the layered nitride material; Step S42: Calculate the phonon spectrum of the layered nitride material using a finite displacement method; Step S43: Determine whether the phonon dispersion curve has a negative value. If so, it is determined that the phonon spectrum has imaginary frequency, the lattice dynamics is unstable, and the unstable layered nitride material is removed; if not, it is determined that the phonon spectrum does not have imaginary frequency, the lattice dynamics is stable, and the layered nitride material with no imaginary frequency in the phonon spectrum is screened out.

[0012] On the one hand, in step S4, the method includes: using a canonical ensemble to test the thermal stability of a layered nitride material without imaginary frequency, expanding the cell in three directions simultaneously, using molecular dynamics simulation and setting the start and end temperatures during calculation, and then obtaining temperature and energy data over time to ensure thermodynamic stability.

[0013] In one aspect, in step S5, the method comprises the following steps: Step S51: obtaining the second-order force constant of the stable layered nitride material according to the phonon spectrum; Step S52: using a finite displacement method to obtain a third-order force constant of a stable layered nitride material; Step S53: Solving the Boltzmann transport equation according to the second-order force constant and the third-order force constant to obtain the lattice thermal conductivity of the stable layered nitride material.

[0014] In one aspect, in step S5, the method comprises the following steps: Step S54: performing data processing on the stable layered nitride material to generate Greeneson parameters of the layered nitride material; Step S55: calculating the relaxation time of the layered nitride material by first principle calculation software; Step S56: using thermoelectric calculation software to calculate the electrical transport of the layered nitride material, and generate electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor.

[0015] In one aspect, in step S5, the method comprises the following steps: Step S57: Calculate the thermoelectric figure of merit of the layered nitride material according to the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity and temperature data: in, is the Seebeck coefficient, is the conductivity, is the working temperature of the material, is the lattice thermal conductivity, is the electronic thermal conductivity; Step S58: using the thermoelectric figure of merit to evaluate the thermoelectric performance of the layered nitride material, and obtaining a target layered nitride material that meets preset requirements.

[0016] The present application also provides a high-performance layered nitride thermoelectric material screening system for executing the screening method, comprising: A magnetic testing module is used to obtain layered nitride materials based on the initial crystal structure of the material, and then use first-principles calculations to perform magnetic testing on the layered nitride materials to obtain non-magnetic materials; The bandgap test module is used to optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out preset bandgap materials; A charge density test module is used to calculate a preset charge density of a preset band gap material to determine whether there is a two-dimensional electron gas. If so, the next step is executed. If not, the material without a two-dimensional electron gas is excluded. Lattice stability test module, used to perform phonon spectrum and molecular dynamics calculations to screen out materials with no imaginary frequencies and stable dynamics; The thermoelectric figure of merit calculation module is used to perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, and then obtain the target layered nitride material that meets the preset requirements.

[0017] Beneficial effects of the high performance layered nitride thermoelectric material screening method of the present application: Based on first-principles calculations, magnetic and stability judgments, structural relaxation and electronic structure calculations are performed to obtain the lattice thermal conductivity, power factor and ZT value of the material. It has the advantages of fast speed and accurate calculation results. It can quickly identify the performance of the material and quickly identify high-performance layered nitride thermoelectric materials. Compared with traditional algorithms, it is more efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0019] Figure 1 This is the first flow chart of the high-performance layered nitride thermoelectric material screening method provided by an embodiment of the present invention.

[0020] Figure 2 This is the second flow chart of the high-performance layered nitride thermoelectric material screening method provided by an embodiment of the present invention.

[0021] Figure 3 It is a flow chart of a magnetic testing method for layered nitride materials provided in an embodiment of the present invention.

[0022] Figure 4 It is a flow chart of a method for testing the bandgap range of layered nitride materials provided in an embodiment of the present invention.

[0023] Figure 5 Schematic diagram of charge density of layered nitride materials provided by an embodiment of the present invention.

[0024] Figure 6 It is a flow chart of a material two-dimensional electron gas determination method provided by an embodiment of the present invention.

[0025] Figure 7 It is a flow chart of a material virtual frequency determination method provided by an embodiment of the present invention.

[0026] Figure 8 It is a schematic diagram of the lattice thermal conductivity of the layered nitride material provided by an embodiment of the present invention at different temperatures.

[0027] Fig. 9 It is a schematic diagram of the Grün Essen parameters of the layered nitride material provided in an embodiment of the present invention.

[0028] Fig.10It is a schematic diagram of the ZT value of the layered nitride material provided by an embodiment of the present invention at different temperatures.

[0029] Fig.11 It is a flow chart of a method for obtaining a target layered nitride material provided by an embodiment of the present invention.

[0030] Fig.12 It is a schematic diagram of module connection of a high-performance layered nitride thermoelectric material screening system provided by an embodiment of the present invention.

[0031] Description of the Figures in the Specification: 101. Magnetic test module, 102. Bandgap test module, 103. Charge density test module, 104. Lattice stability test module, 105. Thermoelectric figure of merit calculation module. DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0033] The present application proposes a method of searching for layered metal nitride materials containing two-dimensional electron gas in bulk metal nitrides, in the hope of obtaining high thermoelectric performance in layered complex metal nitride materials. The implementation case described is only a part of the present invention, not all embodiments. It should be noted that in the specific implementation method, the software calculation part involved is based on density functional theory, and the commonly used VASP (Vienna Ab-inito Simulation Package, which is based on density functional theory and uses plane wave pseudopotential method to perform ab initio molecular dynamics and first principle electronic structure calculations) software and QE (Quantum Espresso, a free and open source quantitative calculation software for electronic structure, simulation, relaxation, including superconducting calculations, electron energy loss spectrum, ballistic transport and other functions) software are used for calculation, so as to efficiently and accurately obtain the data in each step of the present invention.

[0034] Therefore, reference Figure 1 , Figure 2 As shown, in some embodiments, a method for screening high-performance layered nitride thermoelectric materials is provided, the method comprising the following steps: Step S1: obtaining a layered nitride material according to the initial crystal structure of the material, and then performing a magnetic test on the layered nitride material using first-principles calculations to obtain a non-magnetic material.

[0035] Specifically, in step S1, a series of nitride crystal structures with the general formula AMN2 are obtained from the Materials Project database. These crystals adopt a tetragonal KCoO2 layered structure and belong to the space group P4 / nmm. This crystal structure has typical layered characteristics, consisting of MN (M represents transition metal elements) conductive layers and AN (A represents alkaline earth or rare earth metal) insulating layers alternately stacked and arranged along the c-axis direction. Such a structural design makes the material exhibit anisotropic conductive and insulating properties in a specific direction. In order to further study the magnetic characteristics of these layered nitride materials, a calculation method based on first principles is used for analysis; specifically, VASP (Vienna Ab initio Simulation Package) software is used to perform structural optimization and magnetic testing on these materials. VASP is a software package widely used for calculating the electronic structure and atomic structure optimization of materials. It is based on density functional theory (DFT) and can accurately simulate the physical and chemical properties of materials. When performing calculations, VASP software requires four main input files: POSCAR, POTCAR, KPOINTS and INCAR files, which respectively provide the spatial structure information, potential energy information, mesh density and detailed settings of calculation control parameters of the material: POSCAR file contains the spatial structure information of the crystal, including unit cell parameters, atomic positions and their arrangement; in POSCAR file, the processing of electron wave functions uses the projected augmented plane wave (PAW) method, which can more accurately describe the behavior of electrons near the nucleus. The POTCAR file represents the pseudopotential information related to the atomic interaction of the material. It defines the force field used in the calculation process, determines the interaction model between atoms, and ensures the precision and accuracy of the calculation results. The KPOINTS file defines the sampling density of the Brillouin zone, that is, the k-point mesh density. For this calculation, a lower mesh density is used to balance the relationship between calculation accuracy and resource consumption. INCAR file is the main parameter file for controlling the calculation process. It contains a series of calculation settings, such as the number of iterations of the electronic self-consistent field (SCF) calculation, the convergence criteria, etc. In order to test the magnetic properties of the material, the parameter ISPIN=2 is added to the INCAR file, which means that spin polarization calculations will be performed to consider the possible magnetic state of the material. In the electronic structure calculation process, the PBE-GGA (Perdew-Burke-Ernzerhof generalized gradient approximation) exchange correlation functional is used. This functional has high accuracy in dealing with the electronic correlation effect of the system and is suitable for describing the electronic structure characteristics of nitride materials. After the calculation is completed, the magnetic results will be output in the OSZICAR file. If MAG=0 is displayed at the end of the file, it means that the material does not have spontaneous magnetism and is a non-magnetic material. These materials will be retained.

[0036] Therefore, reference Figure 3 As shown, in step S1, the method further includes the following steps: Step S11: using VASP software to optimize the layered nitride material, obtaining spatial structure information data of the layered nitride material, and then constructing force field information data and preset grid density data for each spatial structure contained in the layered nitride material.

[0037] Step S12: In the spatial structure information data of the layered nitride material, the electronic wave function is processed using the projected augmented plane wave and the electronic structure is calculated using the PBE-GGA exchange-correlation functional.

[0038] Step S13: setting a preset spin polarization parameter according to the spatial structure information data in the layered nitride material, so as to screen out non-magnetic layered nitride materials.

[0039] Step S2: Optimize the structure of the non-magnetic material, and then perform static calculation and electronic band structure calculation to screen out the preset band gap material.

[0040] Specifically, in step S2, for materials that appear to be non-magnetic in preliminary magnetic tests, the calculation accuracy will be further improved to obtain more detailed electronic structure information. Specifically, the mesh density of these materials is increased, that is, a more detailed k-point sampling density is defined in the KPOINTS file, and the material is fully structurally relaxed again. The purpose of structural relaxation is to minimize the energy of the system by optimizing the atomic positions, thereby obtaining a more stable crystal structure. After the structure converges, a self-consistent calculation (SCF calculation) is performed to obtain the charge density distribution of the material. To ensure the calculation accuracy, the plane wave cutoff energy is uniformly set to 500 eV in the calculation. The plane wave cutoff energy determines the maximum momentum of the electron wave function expansion, which affects the accuracy and speed of the calculation; in addition, the self-consistent energy convergence accuracy is set to 10 ‑7 eV to ensure the high accuracy of the electron self-consistent field calculation process; at the same time, the convergence standard of the atomic interaction force was set to 10 ‑2eV, which means that the optimization process will continue to accurately determine the position of atoms before this standard is reached. After the electronic structure calculation is completed, the data is processed using the VASPKIT tool to obtain the specific electronic band information of the material, especially the band gap value; VASPKIT is a tool for post-processing VASP calculation data, which can effectively extract and analyze the electronic structure information of the material, such as band structure, state density, band gap, etc., and pay attention to those layered transition metal nitride materials with a band gap of 0.1~3eV, because this band gap range usually corresponds to semiconductor materials and is suitable for thermoelectric and electronic device applications. In the screening process, special attention is paid to materials with high band or valley degeneracy, because at a given carrier concentration, the increase in band or valley degeneracy of such materials will reduce the Fermi level. This energy level change can produce a higher Seebeck coefficient in a relatively low temperature range, improving the thermoelectric performance of the material; the Seebeck coefficient is a key parameter for measuring the thermoelectric effect of a material. A high Seebeck coefficient means that the material can produce a large voltage output under a temperature gradient.

[0041] Therefore, reference Figure 4 As shown, in step S2, the method includes the following steps: Step S21: increasing the grid density of the non-magnetic material to perform structural relaxation; Step S22: After the structure converges, a self-consistent calculation is performed to generate a charge density file of the material; Step S23: using the projected augmented wave method and the generalized gradient approximation as the exchange-correlation function to calculate the electronic band structure of the material, and then screening out materials with a band gap range of 0.1 to 3 eV.

[0042] Step S3: Calculate the preset charge density of the preset bandgap material to determine whether there is a two-dimensional electron gas. If so, execute the next step. If not, exclude the material without a two-dimensional electron gas.

[0043] refer to Figure 5As shown, specifically, in step S3, in order to deeply explore the electronic structure of the material, the partial charge density of the material is calculated, focusing on the partial charge density distribution of the two energy bands, the valence band maximum (VBM) and the conduction band minimum (CBM). This step helps to understand the spatial distribution of electrons at different energy levels in the material and their role in the crystal structure. When calculating the partial charge density, the linear mode is used in the KPOINTS file to improve the accuracy of the description of the distribution of electrons in the Brillouin zone. The linear mode allows more accurate tracking of the behavior of electrons in specific energy bands, especially the distribution of electrons at the edge of the energy band. The focus will be on observing the charge density distribution at the bottom of the conduction band in the material and analyzing whether these charges are mainly concentrated in the atomic layer composed of transition metals and nitrogen atoms. If the calculation results show that the charge density at the bottom of the conduction band is obviously concentrated in the atomic layer formed by the transition metal-nitrogen bond, this usually indicates that a cylindrical Fermi surface structure has been formed inside the material. This Fermi surface morphology is closely related to the existence of a two-dimensional electron gas (2D electron gas, 2DEG), which is a phenomenon in which electrons move freely in a two-dimensional plane but are restricted in the third dimension. It usually gives materials unique physical properties, such as enhanced electron mobility and high conductivity. Materials with two-dimensional electron gas usually exhibit unique physical properties and significantly enhanced thermoelectric performance under specific conditions, mainly because quasi-two-dimensional electron gas can promote the efficient transport of electrons and improve the performance of materials in the thermoelectric effect. If this concentration characteristic is not observed in the charge density distribution at the bottom of the conduction band, it indicates that the material does not have the characteristics of quasi-two-dimensional electron gas, and can be excluded in subsequent analysis.

[0044] Therefore, reference Figure 6 As shown, in step S3, the method includes the following steps: Step S31: Calculate the partial charge density of the valence band top and conduction band bottom of the material in the preset band gap range, and determine whether the charge density at the conduction band bottom of the material appears in the atomic layer formed by the transition metal-nitrogen bond.

[0045] Step S32: If yes, execute step S320: determine that the material in the preset bandgap range has two-dimensional electron gas; if not, execute step S321: determine that the material in the preset bandgap range does not have two-dimensional electron gas, and exclude the material in the preset bandgap range.

[0046] Step S4: Perform phonon spectrum and molecular dynamics calculations to screen out materials with no imaginary frequency and stable dynamics.

[0047] Specifically, in step S4, in order to verify the lattice stability of the material, the phonon spectrum calculation and thermal stability test of the layered nitride material are performed. The phonon spectrum calculation is performed using Phonopy software; this software is a crystal phonon analysis program developed based on Python and is widely used for phonon calculations based on first principles. Phonopy can efficiently calculate the phonon spectrum of the material through the finite displacement method to evaluate its lattice stability. In the calculation process of Phonopy, the same input file as the electronic structure calculation in the previous stage is used, but in this step, the POSCAR file needs to be defined as the supercell structure of the material. For the bulk structure, in order to ensure the accuracy of the calculation, the lengths of the three coordinate axes in the supercell are kept greater than 10 angstroms. This requirement ensures that in the optimized structure, the Hellmann-Feynman force acting on each atom can be fully calculated by introducing a small displacement of the atom. The calculation of these forces is the key to accurately obtain the dynamic properties of the material. After completing the calculation of the displacement method, Phonopy software will generate a Hessian matrix to describe the second-order force constants of the material. Through these force constants, the phonon dispersion curve of the material can be obtained. If there is no negative value in the phonon dispersion curve, it means that the phonon spectrum of the material has no imaginary frequency, which proves that its lattice dynamics is stable; on the contrary, if there is a negative value in the phonon dispersion curve, it means that the lattice dynamics of the material is unstable and not suitable as a stable functional material. After confirming the lattice dynamics stability of the material, the canonical ensemble is further used to test the thermal stability of the material. In order to perform molecular dynamics simulation (AIMD), the material is expanded in three directions at the same time to make the total number of atoms reach about 100 to improve the calculation accuracy. In the INCAR file, IBRION=0 is set to start the molecular dynamics simulation, and the starting temperature (TEBEG) and the ending temperature (TEEND) are set to control the temperature change of the simulation process. The appropriate SMASS parameters are selected according to the actual situation of the system to optimize the performance of the molecular dynamics simulation. Through simulation, the data of temperature and energy changes over time are recorded to analyze the thermal stability of the material at different temperatures. If the energy fluctuations of the material at different temperatures are small and remain stable during the entire simulation process, it can be considered that the material has good thermodynamic stability.

[0048] Therefore, reference Figure 7 As shown, in step S4, the method includes the following steps: Step S41: Calculate the phonon dispersion curve of the layered nitride material.

[0049] Step S42: Calculate the phonon spectrum of the layered nitride material using the finite displacement method.

[0050] Step S43: Determine whether the phonon dispersion curve has a negative value. If so, execute step S430: Determine whether the phonon spectrum has imaginary frequency, the lattice dynamics is unstable, and remove the unstable layered nitride material; if not, execute step S431: Determine whether the phonon spectrum has no imaginary frequency, the lattice dynamics is stable, and screen out the layered nitride material with no imaginary frequency in the phonon spectrum.

[0051] Step S5: Perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, and then obtain a target layered nitride material that meets preset requirements.

[0052] Specifically, in step S5, in order to further study the lattice thermal conductivity of the material, a detailed calculation is performed based on the Boltzmann transport equation. This calculation process requires the analysis of the second-order and third-order force constants of the material to accurately describe the influence of lattice vibration and anharmonic effects on thermal conduction. First, the calculation process of the second-order force constant is the same as the phonon spectrum analysis. The supercell structure is used for calculation, and its lattice dynamics stability is ensured, that is, there is no imaginary frequency phenomenon in the phonon spectrum. After completing the calculation of the second-order force constant through the Phonopy software, the result file FORCE_CONSTANTS is named FORCE_CONSTANTS_2ND. Next, the third-order force constant of the material is calculated using the Thirdorder software. The Thirdorder software is a tool specifically used to study the intermolecular interaction force. When calculating the third-order force constant, the size of the supercell structure should be at least consistent with the second-order force constant calculation. This process will generate a series of POSCAR structure files containing small displacements, and other input files remain consistent with the second-order force constant calculation. After completing the static calculation, the third-order force constant of the material is obtained by processing these data, combined with the second-order force constant calculated previously, and finally the complete lattice thermal conductivity calculation is run in the ShengBTE software to obtain the lattice thermal conductivity. To analyze the thermal conductivity of materials, refer to Figure 8 shown.

[0053] Further, the Grüneisen parameter of the material is calculated, refer to Fig. 9As shown. It is a key parameter used to describe the anharmonic effect of phonons. In the calculation of the lattice thermal conductivity of the material, the Green-Eisen constant of the material was further calculated based on the data obtained previously using the ShengBTE software. The Green-Eisen constant is obtained by analyzing the second-order and third-order force constant data in the lattice thermal conductivity calculation. This parameter quantifies the effect of the lattice on the phonon frequency when it expands or contracts due to heat. A larger Green-Eisen constant means that the material will experience stronger phonon scattering during heat transport. When the Green-Eisen constant is large, it indicates that the lattice vibration inside the material is significantly affected by anharmonic effects. This strong phonon scattering will significantly reduce the lattice thermal conductivity of the material, causing the material to exhibit extremely low thermal conductivity characteristics. For thermoelectric materials, low lattice thermal conductivity is conducive to improving the thermoelectric figure of merit of the material, that is, it reduces the heat loss inside the material, allowing thermal energy to be more efficiently converted into electrical energy. Through this step of analysis of the Greenesen constant, four structures were finally screened out, among which the BaHfN2 material showed extremely low lattice thermal conductivity, a property that suggests that the material may have a very high thermoelectric figure of merit in thermoelectric applications. Based on its lattice thermal conductivity and Greenesen constant, BaHfN2 is very likely to become a thermoelectric material with excellent performance in the thermoelectric field.

[0054] Furthermore, in order to analyze the thermoelectric properties of the material, the relaxation time of the material was calculated using Quantum ESPRESSO (QE) software. ). The calculation process of relaxation time is similar to the calculation steps of VASP software, which mainly includes the following steps: first, optimize the geometric structure of the material to ensure that its crystal structure is in the lowest energy state; then, perform self-consistent field calculation to obtain the electron density and energy distribution of the material; then, perform phonon spectrum calculation to explore the dynamic characteristics of the material by analyzing the phonon mode; in the phonon spectrum calculation, confirm that there is no imaginary frequency in the phonon spectrum of the material through Fourier transform and dynamic matrix calculation to ensure that its lattice remains stable during vibration. Finally, use the electroacoustic coupling module to calculate the relaxation time of the material. The relaxation time is a key parameter that describes the scattering process of electrons or phonons in the material. After obtaining the relaxation time, the BoltzTraP software was used to analyze the electrical transport characteristics of the layered nitride material to calculate the material's electrical conductivity ( ), Seebeck coefficient (S), electronic thermal conductivity ( ) and power factor (PF) to evaluate its performance in thermoelectric applications.

[0055] Further, refer to Fig.10 As shown, according to the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity and temperature data obtained above, enter the formula After that, the thermoelectric performance of the material can be accurately evaluated. In this formula, the ZT value is a measure of the thermoelectric figure of merit of the material. A higher ZT value indicates that the material is more efficient in the thermoelectric conversion process. By substituting the calculated parameters into the formula, the thermoelectric performance of the material at different temperatures can be accurately evaluated. At present, among all the candidate materials, BaHfN2 material is found to have the lowest lattice thermal conductivity and the highest thermoelectric figure of merit at room temperature (ZT value close to 2.5). This value is very outstanding in the field of thermoelectric materials, indicating that BaHfN2 material has great potential and is a very excellent high-performance layered nitride thermoelectric material in the field of thermoelectrics.

[0056] Therefore, reference Fig.11 As shown, in step S5, the method includes the following steps: Step S51: obtaining the second-order force constant of the stable layered nitride material according to the phonon spectrum; Step S52: using a finite displacement method to obtain a third-order force constant of a stable layered nitride material; Step S53: Solving the Boltzmann transport equation according to the second-order force constant and the third-order force constant to obtain the lattice thermal conductivity of the stable layered nitride material.

[0057] Step S54: performing data processing on the stable layered nitride material to generate Greeneson parameters of the layered nitride material; Step S55: calculating the relaxation time of the layered nitride material by first principle calculation software; Step S56: using thermoelectric calculation software to calculate the electrical transport of the layered nitride material, and generate electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor.

[0058] Step S57: Calculate the thermoelectric figure of merit of the layered nitride material according to the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity and temperature data: in, is the Seebeck coefficient, is the conductivity, is the working temperature of the material, is the lattice thermal conductivity, is the electronic thermal conductivity; Step S58: using the thermoelectric figure of merit to evaluate the thermoelectric performance of the layered nitride material, and obtaining a target layered nitride material that meets preset requirements.

[0059] In some embodiments, reference Fig.12 As shown, it also relates to a high-performance layered nitride thermoelectric material screening system for performing a high-performance layered nitride thermoelectric material screening method, comprising: The magnetic testing module is used to obtain layered nitride materials based on the initial crystal structure of the material, and then use first-principles calculations to perform magnetic testing on the layered nitride materials to obtain non-magnetic materials.

[0060] The bandgap test module is used to optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out preset bandgap materials.

[0061] The charge density test module is used to calculate the preset charge density of the preset band gap material to determine whether there is a two-dimensional electron gas. If so, the next step is executed; if not, the material without a two-dimensional electron gas is excluded.

[0062] The lattice stability test module is used to perform phonon spectrum and molecular dynamics calculations to screen out materials with no imaginary frequencies and stable dynamics.

[0063] The thermoelectric figure of merit calculation module is used to perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, and then obtain the target layered nitride material that meets the preset requirements.

[0064] In some embodiments, a computer medium is also provided, wherein a computer program is stored on the computer medium, and the computer program is executed by a processor to implement the method for screening high-performance layered nitride thermoelectric materials.

[0065] In some embodiments, it also relates to a computer, comprising a computer medium according to the above. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0066] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for screening high-performance layered nitride thermoelectric materials, characterized in that: The method comprises the following steps: Step S1: obtaining a layered nitride material according to the initial crystal structure of the material, and then performing a magnetic test on the layered nitride material using first-principles calculations to obtain a non-magnetic material; Step S2: Optimizing the structure of the non-magnetic material, and then performing static calculation and electronic band structure calculation to screen out the preset band gap material; Step S3: Calculate the preset charge density of the preset bandgap material to determine whether there is a two-dimensional electron gas. If so, execute the next step. If not, exclude the material without a two-dimensional electron gas. Step S4: perform phonon spectrum and molecular dynamics calculations to screen out materials with no imaginary frequency and stable dynamics; Step S5: Perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, and then obtain a target layered nitride material that meets preset requirements.

2. A method for screening high-performance layered nitride thermoelectric materials according to claim 1, characterized in that: In step S1, the method comprises the following steps: Step S11: optimizing the layered nitride material using first principle calculation software to obtain spatial structure information data of the layered nitride material, and then constructing force field information data and preset grid density data for each spatial structure contained in the layered nitride material; Step S12: In the spatial structure information data of the layered nitride material, the electronic wave function is processed using the projected plane wave and the electronic structure is calculated using the PBE-GGA exchange-correlation functional; Step S13: setting a preset spin polarization parameter according to the spatial structure information data in the layered nitride material, so as to screen out non-magnetic layered nitride materials.

3. A method for screening high-performance layered nitride thermoelectric materials according to claim 1 or 2, characterized in that: In step S2, the method comprises the following steps: Step S21: increasing the grid density of the non-magnetic material to perform structural relaxation; Step S22: After the structure converges, a self-consistent calculation is performed to generate a charge density file of the material; Step S23: using the projected augmented wave method and the generalized gradient approximation as the exchange-correlation function to calculate the electronic band structure of the material, and then screening out materials within a preset band gap range.

4. A method for screening high-performance layered nitride thermoelectric materials according to claim 3, characterized in that: In step S3, the method comprises the following steps: Step S31: calculating the partial charge density of the valence band top and the conduction band bottom of the material in the preset band gap range, and determining whether the charge density of the conduction band bottom of the material appears in the atomic layer formed by the transition metal-nitrogen bond; Step S32: If yes, it is determined that the material in the preset bandgap range has two-dimensional electron gas; if no, it is determined that the material in the preset bandgap range does not have two-dimensional electron gas, and the material in the preset bandgap range is excluded.

5. A method for screening high-performance layered nitride thermoelectric materials according to claim 4, characterized in that: In step S4, the method comprises the following steps: Step S41: calculating the phonon dispersion curve of the layered nitride material; Step S42: Calculate the phonon spectrum of the layered nitride material using a finite displacement method; Step S43: Determine whether the phonon dispersion curve has a negative value. If so, it is determined that the phonon spectrum has imaginary frequency, the lattice dynamics is unstable, and the unstable layered nitride material is removed; if not, it is determined that the phonon spectrum does not have imaginary frequency, the lattice dynamics is stable, and the layered nitride material with no imaginary frequency in the phonon spectrum is screened out.

6. A method for screening high-performance layered nitride thermoelectric materials according to claim 5, characterized in that: In step S4, the method includes: using a canonical ensemble to perform a thermal stability test on a layered nitride material without imaginary frequency, expanding the cell in three directions simultaneously, using molecular dynamics simulation and setting the start and end temperatures during calculation, and then obtaining temperature and energy data over time to ensure thermodynamic stability.

7. A method for screening high-performance layered nitride thermoelectric materials according to claim 5, characterized in that: In step S5, the method comprises the following steps: Step S51: obtaining the second-order force constant of the stable layered nitride material according to the phonon spectrum; Step S52: using a finite displacement method to obtain a third-order force constant of a stable layered nitride material; Step S53: Solving the Boltzmann transport equation according to the second-order force constant and the third-order force constant to obtain the lattice thermal conductivity of the stable layered nitride material.

8. A method for screening high-performance layered nitride thermoelectric materials according to claim 7, characterized in that: In step S5, the method comprises the following steps: Step S54: performing data processing on the stable layered nitride material to generate Greeneson parameters of the layered nitride material; Step S55: calculating the relaxation time of the layered nitride material by first principle calculation software; Step S56: using thermoelectric calculation software to calculate the electrical transport of the layered nitride material, and generate electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor.

9. A method for screening high-performance layered nitride thermoelectric materials according to claim 8, characterized in that: In step S5, the method comprises the following steps: Step S57: Calculate the thermoelectric figure of merit of the layered nitride material according to the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity and temperature data: in, is the Seebeck coefficient, is the conductivity, is the working temperature of the material, is the lattice thermal conductivity, is the electronic thermal conductivity; Step S58: using the thermoelectric figure of merit to evaluate the thermoelectric performance of the layered nitride material, and obtaining a target layered nitride material that meets preset requirements.

10. A high-performance layered nitride thermoelectric material screening system for executing the screening method according to any one of claims 1 to 9, characterized in that: include: A magnetic testing module is used to obtain layered nitride materials based on the initial crystal structure of the material, and then use first-principles calculations to perform magnetic testing on the layered nitride materials to obtain non-magnetic materials; The bandgap test module is used to optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out preset bandgap materials; A charge density test module is used to calculate a preset charge density of a preset band gap material to determine whether there is a two-dimensional electron gas. If so, the next step is executed. If not, the material without a two-dimensional electron gas is excluded. Lattice stability test module, used to perform phonon spectrum and molecular dynamics calculations to screen out materials with no imaginary frequencies and stable dynamics; The thermoelectric figure of merit calculation module is used to perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, and then obtain the target layered nitride material that meets the preset requirements.

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