A high-performance layered nitride thermoelectric material screening method and system

Abstract

This invention discloses a method and system for screening high-performance layered nitride thermoelectric materials, comprising: obtaining a series of crystal structures of initial layered nitrides; performing magnetic tests on the materials using first-principles calculations to select non-magnetic materials; optimizing the structure of non-magnetic materials, and after calculation convergence, performing static calculations and electronic band structure calculations to select materials with a band gap range of 0.1~3 eV and high band structure degeneracy; calculating the partial charge density of the materials to determine whether there is a two-dimensional electron gas, i.e., alternating conductive and insulating layers; determining stability by performing phonon spectrum and molecular dynamics simulations on the materials to select materials with no imaginary frequencies in the phonon spectrum and stable dynamics; calculating the thermal transport properties of the materials, obtaining the lattice thermal conductivity and Green'sson parameters, and searching for materials with strong anharmonicity; and finally performing electrical transport calculations to obtain the ZT value of the materials.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric material screening technology, specifically to a method and system for screening high-performance layered nitride thermoelectric materials. Background Technology

[0002] Thermoelectric materials are materials that can directly convert thermal energy (such as solar energy and waste heat) into electrical energy. Developing low-cost, high-efficiency thermoelectric devices would be of great help in alleviating the current energy crisis and environmental pollution. Thermoelectric performance is usually expressed using the dimensionless thermoelectric figure of merit (ZT). ZT = S 2 T / ( + As can be seen from the formula, due to the properties of the material itself, it is not possible to simultaneously increase the Seebeck coefficient and electrical conductivity. Only by appropriately increasing the power factor or significantly reducing the thermal conductivity can the thermoelectric figure of merit be optimized.

[0003] The low thermoelectric conversion efficiency of traditional materials has driven the development of more advanced and complex combinations of thermoelectric materials. Layered compounds often exhibit superior electronic properties compared to traditional metals and semiconductors. Transition metal (TM) oxides have attracted widespread attention due to their unconventional carrier transport characteristics. The most representative example is the two-dimensional electron gas (2DEG) in the heterointerface of SrTiO3. The disruption of interface degeneracy allows the formation of conduction band channels in the 2DEG layer, which plays an important role in its high electron mobility, superconductivity, ferromagnetism, and Seebeck coefficient, exhibiting enhanced electron mobility and improved electrical conductivity. Furthermore, layered TM oxides composed of alternating conductive layers consisting of TM ions and insulating barrier layers have been extensively studied, revealing unique electromagnetic properties. KCoO2-type layered composite nitrides exhibit strong band anisotropy, large effective mass, and better electrical transport performance. However, the excellent 2DEG properties only appear in a very thin region near the interface of the heterostructure. It would be more interesting if such 2DEG were contained in bulk materials at high density, in which case the 2DEG properties would appear throughout the bulk phase, but such materials are known to be 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 employs a tetragonal KCoO2-type layered crystal structure with a natural superlattice along the c-axis consisting of a conductive layer (MN) and an insulating layer (AN), suggesting the potential for two-dimensional electronic structure and anisotropic transport properties. To date, the number of known AMN2 compounds is limited compared to layered composite metal oxides and chalcogenides, suggesting the existence of unknown AMN2 layered composite metal nitrides that may exhibit novel physical properties.

[0005] Therefore, there is an urgent need for an efficient screening method 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 this invention is to provide a method and system for screening high-performance layered nitride thermoelectric materials.

[0007] To address the aforementioned technical problems, this invention provides a method for screening high-performance layered nitride thermoelectric materials, comprising:

[0008] Step S1: Based on the initial crystal structure of the material, obtain the layered nitride material, and then use first-principles calculations to perform magnetic tests on the layered nitride material to obtain a non-magnetic material;

[0009] Step S2: Optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out materials with preset band gaps;

[0010] Step S3: Calculate the preset charge density of the preset bandgap material and determine whether a two-dimensional electron gas exists. If yes, proceed to the next step; otherwise, exclude the material that does not have a two-dimensional electron gas.

[0011] Step S4: Perform phonon spectrum and molecular dynamics calculations to screen for materials with no imaginary frequencies and stable dynamics;

[0012] Step S5: Perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, thereby obtaining the target layered nitride material that meets the preset requirements.

[0013] In one aspect, step S1 includes the following steps:

[0014] Step S11: Optimize the layered nitride material using first-principles calculation software to obtain spatial structure information data of the layered nitride material, and then construct force field information data and preset grid density data for each spatial structure contained in the layered nitride material;

[0015] Step S12: In the spatial structure information data of layered nitride materials, the electronic wave function is processed using projected plane wave and the electronic structure is calculated using PBE-GGA exchange correlation functional.

[0016] Step S13: Based on the spatial structure information data in the layered nitride material, set the preset spin polarization parameters to screen out non-magnetic layered nitride materials.

[0017] In one aspect, the method is characterized in that, in step S2, the method includes the following steps:

[0018] Step S21: Increase the mesh density of the non-magnetic material to perform structural relaxation;

[0019] Step S22: After the structure converges, perform self-consistent calculations to generate the charge density file of the material;

[0020] Step S23: Using the projection-attached wave method, the electronic band structure of the material is calculated by using the generalized gradient approximation as the exchange correlation function, and then materials within the preset band gap range are screened out.

[0021] In one aspect, step S3 includes the following steps:

[0022] Step S31: Calculate the partial charge density at the top of the valence band and the bottom of the conduction band of the material within the preset band gap range, and determine whether the charge density at the bottom of the conduction band of the material appears in the atomic layer composed of transition metal-nitrogen bonds;

[0023] 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.

[0024] In one aspect, step S4 includes the following steps:

[0025] Step S41: Calculate the phonon dispersion curve of the layered nitride material;

[0026] Step S42: Calculate the phonon spectrum of the layered nitride material using the finite displacement method;

[0027] Step S43: Determine whether there is a negative value in the phonon dispersion curve. If so, determine that the phonon spectrum has an imaginary frequency, the lattice dynamics are unstable, and remove the unstable layered nitride material. If not, determine that the phonon spectrum does not have an imaginary frequency, the lattice dynamics are stable, and screen out the layered nitride material with no imaginary frequency in the phonon spectrum.

[0028] In one aspect, in step S4, the method includes: using a canonical ensemble to test the thermal stability of layered nitride materials without imaginary frequencies, expanding the cell simultaneously in three directions, using molecular dynamics simulation and setting start and end temperatures during calculation, thereby obtaining temperature and energy data over time to ensure thermodynamic stability.

[0029] In one aspect, step S5 includes the following steps:

[0030] Step S51: Obtain the second-order force constant of the stable layered nitride material based on the phonon spectrum;

[0031] Step S52: Obtain the third-order force constants of stable layered nitride materials using the finite displacement method;

[0032] Step S53: Solve the Boltzmann transport equation based on the second-order and third-order force constants to obtain the lattice thermal conductivity of the stable layered nitride material.

[0033] In one aspect, step S5 includes the following steps:

[0034] Step S54: Perform data processing on the stable layered nitride material to generate the Green's Eisen parameters of the layered nitride material;

[0035] Step S55: Calculate the relaxation time of the layered nitride material using first-principles calculation software;

[0036] Step S56: Use thermoelectric calculation software to calculate the electrical transport of the layered nitride material, and generate the electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor.

[0037] In one aspect, step S5 includes the following steps:

[0038] Step S57: Calculate the thermoelectric figure of merit of the layered nitride material based on the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity, and temperature data.

[0039]

[0040] in, The Seebeck coefficient is... For electrical conductivity, The operating temperature of the material. For lattice thermal conductivity, Electron thermal conductivity;

[0041] Step S58: Use thermoelectric figure of merit to evaluate the thermoelectric properties of the layered nitride material to obtain a target layered nitride material that meets the preset requirements.

[0042] This application also provides a high-performance layered nitride thermoelectric material screening system for performing the aforementioned screening method, comprising:

[0043] The magnetic testing module is used to obtain layered nitride materials based on the initial crystal structure of the materials, and then to perform magnetic testing on the layered nitride materials using first-principles calculations to obtain non-magnetic materials;

[0044] The bandgap testing module is used to optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out materials with preset bandgap.

[0045] The charge density testing module is used to calculate the preset charge density of the preset bandgap material and determine whether a two-dimensional electron gas exists. If it does, the next step is executed; otherwise, the material without a two-dimensional electron gas is excluded.

[0046] The lattice stability testing module is used to perform phonon spectrum and molecular dynamics calculations to screen out materials that are dynamically stable and have no imaginary frequencies.

[0047] 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, thereby obtaining the target layered nitride material that meets the preset requirements.

[0048] The beneficial effects of the screening method for high-performance layered nitride thermoelectric materials in this application are as follows:

[0049] Based on first-principles calculations, this method performs magnetic and stability assessments, structural relaxation, and electronic structure calculations to obtain the lattice thermal conductivity, power factor, and ZT value of materials. It has the advantages of high speed and accurate calculation results, and can quickly identify the properties of materials, thereby quickly identifying high-performance layered nitride thermoelectric materials. Compared with traditional algorithms, it is more efficient. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0051] Figure 1 This is the first flowchart of the screening method for high-performance layered nitride thermoelectric materials provided in the embodiments of the present invention.

[0052] Figure 2 This is the second flowchart of the screening method for high-performance layered nitride thermoelectric materials provided in the embodiments of the present invention.

[0053] Figure 3 This is a flowchart of the magnetic testing method for layered nitride materials provided in the embodiments of the present invention.

[0054] Figure 4 This is a flowchart of a method for testing the band gap range of layered nitride materials provided in an embodiment of the present invention.

[0055] Figure 5 This is a schematic diagram of the charge density of the layered nitride material provided in the embodiments of the present invention.

[0056] Figure 6 This is a flowchart of the two-dimensional electron gas determination method for materials provided in the embodiments of the present invention.

[0057] Figure 7 This is a flowchart of the material imaginary frequency determination method provided in the embodiments of the present invention.

[0058] Figure 8 This is a schematic diagram of the lattice thermal conductivity of the layered nitride material provided in the embodiments of the present invention at different temperatures.

[0059] Figure 9 This is a schematic diagram of the Green's-Essen parameters of the layered nitride material provided in an embodiment of the present invention.

[0060] Figure 10 This is a schematic diagram of the ZT values ​​of the layered nitride material provided in the embodiments of the present invention at different temperatures.

[0061] Figure 11 This is a flowchart of a method for obtaining a target layered nitride material provided in an embodiment of the present invention.

[0062] Figure 12 This is a schematic diagram of the module connections of the high-performance layered nitride thermoelectric material screening system provided in an embodiment of the present invention.

[0063] Explanation of reference numerals on the accompanying drawings:

[0064] 101. Magnetic testing module; 102. Band gap testing module; 103. Charge density testing module; 104. Lattice stability testing module; 105. Thermoelectric figure of merit calculation module. Detailed Implementation

[0065] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0066] This application proposes a method for searching for layered metal nitride materials containing two-dimensional electron gases within bulk metal nitrides, aiming to obtain high thermoelectric properties in complex layered metal nitride materials. The described embodiments are only a part of the invention, not all of the examples. It should be noted that, in the specific embodiments, the software calculations involved are based on density functional theory and employ widely used VASP (Vienna Ab-inito Simulation Package, a software for ab initio molecular dynamics and first-principles electronic structure calculations based on density functional theory and utilizing the plane wave pseudopotential method) and QE (Quantum Espresso, a free and open-source quantitative calculation software for electronic structure, simulation, relaxation, including functions such as superconductivity calculation, electron energy loss spectroscopy, and ballistic transport) software to efficiently and accurately obtain the data in each step of the invention.

[0067] Therefore, for reference Figure 1 , Figure 2 As shown in some embodiments, a method for screening high-performance layered nitride thermoelectric materials is involved, the method comprising the following steps:

[0068] Step S1: Based on the initial crystal structure of the material, obtain the layered nitride material, and then use first-principles calculations to perform magnetic tests on the layered nitride material to obtain a non-magnetic material.

[0069] 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 type layered structure, belonging to the space group P4 / nmm. This crystal structure has typical layered characteristics, consisting of alternating stacked MN (M represents transition metal elements) conductive layers and AN (A represents alkaline earth or rare earth metals) insulating layers, arranged along the c-axis. This structural design makes the material exhibit anisotropic conductive and insulating properties in a specific direction. To further study the magnetic characteristics of these layered nitride materials, first-principles calculation methods are used for analysis. Specifically, VASP (Vienna Ab initio Simulation Package) software is used to optimize the structure and perform magnetic tests on these materials. VASP is a widely used software package for calculating and optimizing the electronic and atomic structures of materials. It is based on density functional theory (DFT) and can accurately simulate the physical and chemical properties of materials. During calculations, the VASP software requires four main input files: POSCAR, POTCAR, KPOINTS, and INCAR. These files provide detailed settings for the material's spatial structure, potential energy, mesh density, and computational control parameters, respectively. The POSCAR file contains the crystal's spatial structure information, including cell parameters, atomic positions, and their arrangement. In the POSCAR file, the electronic wavefunction is processed using the Projected Added Plane Wave (PAW) method, which more accurately describes the behavior of electrons near the atomic nuclei. The POTCAR file represents pseudopotential information related to atomic interactions; it defines the force field used in the calculation, determines the interaction model between atoms, and ensures the accuracy and precision of the results. The KPOINTS file defines the sampling density of the Brillouin zone, i.e., the k-point mesh density. For this calculation, a lower mesh density is used to balance computational accuracy and resource consumption. The INCAR file, serving as the primary parameter file controlling the computation process, contains a series of computational settings, such as the number of iterations for the self-consistent electronic field (SCF) calculation and the convergence criterion. To test the magnetic properties of the material, the parameter ISPIN=2 is added to the INCAR file, indicating that spin polarization calculations will be performed to account for possible magnetic states in the material. During the electronic structure calculations, the PBE-GGA (Perdew-Burke-Ernzerhof generalized gradient approximation) exchange-correlation functional is used. This functional exhibits high accuracy in handling electronic correlation effects in the system and is suitable for describing the electronic structure characteristics of nitride materials. After the calculations are complete, the magnetic results are output in the OSZICAR file. If MAG=0 is displayed at the end of this file, it indicates that the material does not possess spontaneous magnetism and is considered a non-magnetic material; these materials are retained.

[0070] Therefore, for reference Figure 3 As shown, in step S1, the method further includes the following steps:

[0071] Step S11: Use VASP software to optimize the layered nitride material to obtain the spatial structure information data of the layered nitride material, and then construct force field information data and preset grid density data for each spatial structure contained in the layered nitride material.

[0072] Step S12: In the spatial structure information data of the layered nitride material, the electronic wave function is processed using projected plane wave and the electronic structure is calculated using PBE-GGA exchange correlation functional.

[0073] Step S13: Based on the spatial structure information data in the layered nitride material, set the preset spin polarization parameters to screen out non-magnetic layered nitride materials.

[0074] Step S2: Optimize the structure of the non-magnetic material, and then perform static calculations and electronic band structure calculations to screen out the materials with the preset band gap.

[0075] Specifically, in step S2, for materials that appear non-magnetic in the initial magnetic tests, the calculation accuracy is further improved to obtain more detailed electronic structure information. Specifically, the grid density is increased for these materials; that is, a more detailed k-point sampling density is defined in the KPOINTS file. The material is then subjected to thorough structural relaxation again. The purpose of structural relaxation is to optimize atomic positions to minimize the system's energy, thereby obtaining a more stable crystal structure. After structural convergence, a self-consistent calculation (SCF calculation) is performed to obtain the material's charge density distribution. To ensure 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, thus affecting the accuracy and speed of the calculation. Furthermore, the self-consistent energy convergence accuracy is set to 10 eV. ‑7 eV is used to ensure high accuracy in the electronic self-consistent field calculation process; at the same time, the convergence criterion for interatomic interaction forces is set to 10 eV. ‑2eV means that the optimization process will continue until this standard is reached to precisely determine the positions of atoms. After the electronic structure calculations are 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 materials, such as band structure, density of states, and band gap. Attention is paid to layered transition metal nitride materials with band gaps of 0.1~3 eV, as this band gap range typically corresponds to semiconductor materials and is suitable for thermoelectric and electronic device applications. During 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 in such materials will lower the Fermi level. This energy level change can produce a high Seebeck coefficient over 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.

[0076] Therefore, for reference Figure 4 As shown, in step S2, the method includes the following steps:

[0077] Step S21: Increase the mesh density of the non-magnetic material to perform structural relaxation;

[0078] Step S22: After the structure converges, perform self-consistent calculations to generate the charge density file of the material;

[0079] Step S23: Using the projected fused wave method, the electronic band structure of the material is calculated by using the generalized gradient approximation as the exchange correlation function, and then materials with a band gap range of 0.1~3eV are screened out.

[0080] Step S3: Calculate the preset charge density of the preset bandgap material and determine whether a two-dimensional electron gas exists. If yes, proceed to the next step; otherwise, exclude the material that does not have a two-dimensional electron gas.

[0081] refer to Figure 5As shown, specifically in step S3, to delve deeper into the electronic structure of the material, partial charge density calculations are performed, focusing on the partial charge density distribution of the valence band maximum (VBM) and 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 performing partial charge density calculations, a linear mode is used in the KPOINTS file to improve the accuracy of the description of electron distribution in the Brillouin zone. The linear mode allows for more precise tracking of electron behavior in specific energy bands, especially the electron distribution at band edges. The focus is on observing the charge density distribution at the conduction band minimum and analyzing whether these charges are mainly concentrated in atomic layers composed of transition metals and nitrogen atoms. If calculations show that the charge density at the bottom of the conduction band is significantly concentrated in the atomic layers formed by transition metal-nitrogen bonds, this usually indicates the formation of a cylindrical Fermi surface structure within the material. This Fermi surface morphology is closely related to the presence of a 2D electron gas (2DEG), a phenomenon where electrons move freely in a two-dimensional plane but are confined in a third dimension. It typically endows materials with unique physical properties, such as enhanced electron mobility and higher electrical conductivity. Materials possessing 2DEG often exhibit unique physical properties and significantly enhanced thermoelectric properties under specific conditions, mainly because the quasi-2DEG facilitates efficient electron transport and improves the material's performance in thermoelectric effects. If this concentration is not observed in the charge density distribution at the bottom of the conduction band, it indicates that the material does not possess the characteristics of a quasi-2DEG and can therefore be excluded from subsequent analysis.

[0082] Therefore, for reference Figure 6 As shown, in step S3, the method includes the following steps:

[0083] Step S31: Calculate the partial charge density at the top of the valence band and the bottom of the conduction band of the material within the preset band gap range, and determine whether the charge density at the bottom of the conduction band of the material appears in the atomic layer composed of transition metal-nitrogen bonds.

[0084] Step S32: If yes, then proceed to step S320: determine that the material within the preset bandgap range contains two-dimensional electron gas; if no, then proceed to step S321: determine that the material within the preset bandgap range does not contain two-dimensional electron gas, and exclude the material within the preset bandgap range.

[0085] Step S4: Perform phonon spectrum and molecular dynamics calculations to screen for materials with no imaginary frequencies and stable dynamics.

[0086] Specifically, in step S4, to verify the lattice stability of the material, phonon spectrum calculations and thermal stability tests are performed on the layered nitride material. The phonon spectrum calculations are conducted using Phonopy software; this software is a Python-based crystal phonon analysis program widely used for first-principles phonon calculations. Phonopy, through the finite displacement method, can efficiently calculate the phonon spectrum of materials to evaluate their lattice stability. During the Phonopy calculations, the same input file as the previous electronic structure calculation is used. However, in this step, the POSCAR file must be defined as the supercell structure of the material. For bulk structures, to ensure calculation accuracy, the lengths of all three coordinate axes in the supercell are kept greater than 10 angstroms. This requirement ensures that, in the optimized structure, the Hellmann-Feynman forces acting on each atom can be fully calculated by introducing small atomic displacements. The calculation of these forces is crucial for accurately obtaining the dynamic properties of the material. After completing the displacement method calculations, the Phonopy software generates a Hessian matrix to describe the material's second-order force constants. These force constants allow the generation of the material's phonon dispersion curve. If no negative values ​​appear in the phonon dispersion curve, it indicates that the material's phonon spectrum lacks imaginary frequencies, thus proving its lattice dynamics stability. Conversely, if negative values ​​exist in the phonon dispersion curve, it indicates that the material's lattice dynamics is unstable and unsuitable as a stable functional material. After confirming the material's lattice dynamics stability, a canonical ensemble is used to test its thermal stability. To perform AIMD (Artificial Molecular Dynamics Modeling), cell expansion operations are performed simultaneously in three directions to increase the total number of atoms to approximately 100, improving computational accuracy. IBRION=0 is set in the INCAR file to enable the AIMD simulation. The start temperature (TEBEG) and end temperature (TEEND) are set to control temperature changes during the simulation. Appropriate SMASS parameters are also selected based on the system's actual conditions to optimize the performance of the AIMD simulation. By simulating and recording the changes in temperature and energy over time, the thermal stability of the material at different temperatures can be analyzed. If the energy fluctuations of the material at different temperatures are small and remain stable throughout the simulation, the material can be considered to have good thermodynamic stability.

[0087] Therefore, for reference Figure 7 As shown, in step S4, the method includes the following steps:

[0088] Step S41: Calculate the phonon dispersion curve of the layered nitride material.

[0089] Step S42: Calculate the phonon spectrum of the layered nitride material using the finite displacement method.

[0090] Step S43: Determine whether there is a negative value in the phonon dispersion curve. If yes, proceed to step S430: Determine whether there is an imaginary frequency in the phonon spectrum, indicating unstable lattice dynamics, and remove the unstable layered nitride material. If no, proceed to step S431: Determine whether there is no imaginary frequency in the phonon spectrum, indicating stable lattice dynamics, and screen out the layered nitride material with no imaginary frequency in the phonon spectrum.

[0091] Step S5: Perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, thereby obtaining the target layered nitride material that meets the preset requirements.

[0092] Specifically, in step S5, to further investigate the lattice thermal conductivity of the material, detailed calculations were performed based on the Boltzmann transport equation. This calculation process requires analysis of the second and third force constants of the material to accurately describe the influence of lattice vibrations and anharmonic effects on heat conduction. First, the calculation process for the second force constant is the same as that for phonon spectrum analysis, using a supercell structure for calculation and ensuring its lattice dynamic stability, i.e., the absence of imaginary frequencies in the phonon spectrum. After completing the second force constant calculation using Phonopy software, the resulting file FORCE_CONSTANTS is named FORCE_CONSTANTS_2ND. Next, the third-order force constants of the material are calculated using Thirdorder software. Thirdorder is a tool specifically designed for studying intermolecular forces. When calculating the third-order force constants, the size of the supercell structure should be at least the same as that used in the second-order force constant calculations. This process generates a series of POSCAR structure files containing minute displacements, while other input files remain consistent with those used in the second-order force constant calculations. After completing the static calculations, the third-order force constants of the material are obtained by processing these data. Combined with the previously calculated second-order force constants, a complete lattice thermal conductivity calculation is finally performed in ShengBTE software to obtain the lattice thermal conductivity. To analyze the thermal conductivity properties of materials, refer to Figure 8 As shown.

[0093] Furthermore, the Grüneisen parameter of the material is calculated, referring to... Figure 9As shown, the Gram-Eisen constant is a key parameter used to describe phonon anharmonic effects. In the calculation of the material's lattice thermal conductivity, based on data previously obtained using ShengBTE software, the Gram-Eisen constant was further calculated. The Gram-Eisen constant is derived by analyzing the second and third-order force constant data in the lattice thermal conductivity calculation. This parameter quantifies the influence of lattice expansion or contraction on phonon frequencies. A larger Gram-Eisen constant indicates stronger phonon scattering during thermal transport. When the Gram-Eisen constant is large, it indicates that lattice vibrations are significantly affected by anharmonic effects within the material. This strong phonon scattering significantly reduces the material's lattice thermal conductivity, resulting in extremely low thermal conductivity. For thermoelectric materials, low lattice thermal conductivity is beneficial for improving the thermoelectric figure of merit, meaning it reduces internal heat loss, allowing thermal energy to be converted into electrical energy more efficiently. Through this step of analyzing the Green's Eisen constant, four structures were ultimately selected. Among them, BaHfN2 exhibits extremely low lattice thermal conductivity, a characteristic that suggests it may possess a very high thermoelectric figure of merit in thermoelectric applications. Based on its lattice thermal conductivity and Green's Eisen constant performance, BaHfN2 is highly likely to become a thermoelectric material with excellent performance in the thermoelectric field.

[0094] Furthermore, to analyze the thermoelectric properties of the material, the relaxation time of the material was calculated using Quantum ESPRESSO (QE) software. The calculation process for relaxation time is similar to that of VASP software, mainly including the following steps: First, the material's geometry is optimized to ensure its crystal structure is in the lowest energy state; next, self-consistent field calculations are performed to obtain the material's electron density and energy distribution; subsequently, phonon spectrum calculations are performed to explore the material's dynamic properties by analyzing phonon modes; in the phonon spectrum calculation, Fourier transform and dynamic matrix calculations are used to confirm that there are no imaginary frequencies in the material's phonon spectrum, ensuring that its lattice remains stable during vibration; finally, the relaxation time of the material is calculated using the electroacoustic coupling module. Relaxation time is a key parameter describing the scattering process of electrons or phonons in a material. After obtaining the relaxation time, the electrical transport properties of the layered nitride material are analyzed using BoltzTraP software to calculate the material's conductivity. Seebeck coefficient (S), electronic thermal conductivity ( The power factor (PF) and power factor (PF) were used to evaluate its performance in thermoelectric applications.

[0095] Further, refer to Figure 10 As shown, based on the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity, and temperature data obtained above, substitute them into the formula. This allows for accurate evaluation of the material's thermoelectric properties. In this formula, the ZT value is a measure of the material's thermoelectric figure of merit; a higher ZT value indicates greater efficiency 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. Currently, among all candidate materials, BaHfN2 has been found to have the lowest lattice thermal conductivity and achieves the highest thermoelectric figure of merit (ZT value close to 2.5) at room temperature. This value is outstanding in the field of thermoelectric materials, indicating that BaHfN2 has great potential and is an excellent high-performance layered nitride thermoelectric material.

[0096] Therefore, for reference Figure 11 As shown, in step S5, the method includes the following steps:

[0097] Step S51: Obtain the second-order force constant of the stable layered nitride material based on the phonon spectrum;

[0098] Step S52: Obtain the third-order force constants of stable layered nitride materials using the finite displacement method;

[0099] Step S53: Solve the Boltzmann transport equation based on the second-order and third-order force constants to obtain the lattice thermal conductivity of the stable layered nitride material.

[0100] Step S54: Perform data processing on the stable layered nitride material to generate the Green's Eisen parameters of the layered nitride material;

[0101] Step S55: Calculate the relaxation time of the layered nitride material using first-principles calculation software;

[0102] Step S56: Use thermoelectric calculation software to calculate the electrical transport of the layered nitride material, and generate the electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor.

[0103] Step S57: Calculate the thermoelectric figure of merit of the layered nitride material based on the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity, and temperature data.

[0104]

[0105] in, The Seebeck coefficient is... For electrical conductivity, The operating temperature of the material. For lattice thermal conductivity, Electron thermal conductivity;

[0106] Step S58: Use thermoelectric figure of merit to evaluate the thermoelectric properties of the layered nitride material to obtain a target layered nitride material that meets the preset requirements.

[0107] In some embodiments, reference Figure 12 As shown, a high-performance layered nitride thermoelectric material screening system for performing a high-performance layered nitride thermoelectric material screening method is also disclosed, comprising:

[0108] The magnetic testing module is used to obtain layered nitride materials based on their initial crystal structure, and then to perform magnetic testing on the layered nitride materials using first-principles calculations to obtain non-magnetic materials.

[0109] The bandgap testing module is used to optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out materials with preset bandgap.

[0110] The charge density testing module is used to calculate the preset charge density of the preset bandgap material and determine whether a two-dimensional electron gas exists. If so, the next step is executed; otherwise, the material without a two-dimensional electron gas is excluded.

[0111] The lattice stability testing module is used to perform phonon spectrum and molecular dynamics calculations to screen for materials that are dynamically stable and have no imaginary frequencies.

[0112] 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, thereby obtaining the target layered nitride material that meets the preset requirements.

[0113] In some embodiments, a computer medium is also involved, on which a computer program is stored, the computer program being executed by a processor to implement the aforementioned method for screening high-performance layered nitride thermoelectric materials.

[0114] In some embodiments, a computer is also involved, including a computer medium according to the description.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to 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 includes the following steps: Step S1: Based on the initial crystal structure of the material, obtain the layered nitride material, and then use first-principles calculations to perform magnetic tests on the layered nitride material to obtain the non-magnetic material; Step S2: Optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out materials with preset band gaps; Step S3: Calculate the partial charge density at the top of the valence band and the bottom of the conduction band of the material with the preset band gap, and determine whether the charge density at the bottom of the conduction band appears in the atomic layer formed by the transition metal-nitrogen atom bond; if so, it is determined that a two-dimensional electron gas exists and proceed to the next step; if not, it is determined that a two-dimensional electron gas does not exist and the material is excluded. Step S4: Calculate the phonon dispersion curve and phonon spectrum of the material, and determine whether there is an imaginary frequency in the phonon dispersion curve; if there is, determine that the lattice dynamics are unstable and remove the material; if there is no imaginary frequency, determine that the lattice dynamics are stable and screen out the material. Step S5: Perform electrical transport calculations and thermal transport calculations to obtain the thermoelectric figure of merit of the material, thereby obtaining the target layered nitride material that meets the preset requirements; In step S1, the method includes the following steps: Step S11: Optimize the layered nitride material using first-principles calculation software to obtain spatial structure information data of the layered nitride material, and then construct 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 layered nitride materials, the electronic wave function is processed using projected plane wave and the electronic structure is calculated using PBE-GGA exchange correlation functional. Step S13: Based on the spatial structure information data in the layered nitride material, set the preset spin polarization parameters to screen out non-magnetic layered nitride materials. In step S2, the method includes the following steps: Step S21: Increase the mesh density of the non-magnetic material to perform structural relaxation; Step S22: After the structure converges, perform self-consistent calculations to generate the charge density file of the material; Step S23: Using the projection-attached wave method, the electronic band structure of the material is calculated by using the generalized gradient approximation as the exchange correlation function, and then materials within the preset band gap range are screened out.

2. The method for screening high-performance layered nitride thermoelectric materials according to claim 1, characterized in that, After step S4, the method further includes: using a canonical ensemble to test the thermal stability of the layered nitride material without imaginary frequency, expanding the cell simultaneously in three directions, using molecular dynamics simulation and setting the start and end temperatures during the calculation, thereby obtaining data on temperature and energy over time to ensure thermodynamic stability.

3. A method for screening high-performance layered nitride thermoelectric materials according to any one of claims 1-2, characterized in that, In step S5, the method includes the following steps: Step S51: Obtain the second-order force constant of the stable layered nitride material based on the phonon spectrum; Step S52: Obtain the third-order force constants of stable layered nitride materials using the finite displacement method; Step S53: Solve the Boltzmann transport equation based on the second-order and third-order force constants to obtain the lattice thermal conductivity of the stable layered nitride material; Step S54: Perform data processing on the stable layered nitride material to generate the Green's Eisen parameters of the layered nitride material; Step S55: Calculate the relaxation time of the layered nitride material using first-principles calculation software; Step S56: Use thermoelectric calculation software to calculate the electrical transport of the layered nitride material, and generate the electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor.

4. The method for screening high-performance layered nitride thermoelectric materials according to claim 3, characterized in that, In step S5, the method includes the following steps: Step S57: Calculate the thermoelectric figure of merit of the layered nitride material based on the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity, and temperature data. Where is the Seebeck coefficient, is the electrical conductivity, is the operating temperature of the material, is the lattice thermal conductivity, and is the electronic thermal conductivity; Step S58: Use thermoelectric figure of merit to evaluate the thermoelectric properties of the layered nitride material to obtain a target layered nitride material that meets the preset requirements.

5. A high-performance layered nitride thermoelectric material screening system for implementing the screening method according to any one of claims 1-4, characterized in that, include: The magnetic testing module is used to obtain layered nitride materials based on the initial crystal structure of the materials, and then to perform magnetic testing on the layered nitride materials using first-principles calculations to obtain non-magnetic materials; The bandgap testing module is used to optimize the structure of non-magnetic materials, and then perform static calculations and electronic band structure calculations to screen out materials with preset bandgap. The charge density testing module is used to calculate the preset charge density of the preset bandgap material and determine whether a two-dimensional electron gas exists. If it does, the next step is executed; otherwise, the material without a two-dimensional electron gas is excluded. The lattice stability testing module is used to perform phonon spectrum and molecular dynamics calculations to screen out materials that are dynamically stable and have no imaginary frequencies. 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, thereby obtaining the target layered nitride material that meets the preset requirements.

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