Method for quantitatively regulating thermal conductivity of a material

Abstract

The application belongs to the technical field of thermal conductivity regulation, and particularly discloses a method for quantitatively regulating thermal conductivity of a material, which comprises the following steps: obtaining the second-order derivative or third-order derivative of the energy eigenvalue of electrons in the material and the ground state energy with respect to atomic displacement; if the second-order derivative is obtained, the contribution value of each eigenmode to thermal conductivity is calculated in combination with a stable temperature gradient; if the third-order derivative is obtained, the mode thermal conductivity and the lattice thermal conductivity are obtained; the material thermal conductivity contribution spectrum is obtained according to the contribution value of each eigenmode to thermal conductivity or the mode thermal conductivity, and the phonon eigenmode that dominates the thermal conductivity of the material is selected; the resonance absorption of terahertz pulse is used to excite the phonon of a specific frequency, so that the number of the phonon eigenmode that dominates the thermal conductivity of the material is changed, and the thermal conductivity of the material is changed and regulated. The application regulates in situ, changes the thermal conductivity of the material without affecting other mechanical properties, is simple to control, low in cost and fast in response.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of thermal conductivity regulation, and more particularly relates to a method for quantitatively regulating the thermal conductivity of a material. BACKGROUND

[0002] In the concept of solid state physics, atoms or molecules in a crystalline solid are arranged in a regular pattern on a crystal lattice. In a crystal, atoms interact with each other, and the atoms are not stationary, but are constantly vibrating around their equilibrium positions. On the other hand, these atoms are linked together through their interaction forces, i.e., their respective vibrations are not independent of each other. The interaction force between atoms can be well approximated as an elastic force. Phonon is a kind of quasi-particle, which is used to describe the regularity of atomic thermal vibration, i.e., lattice vibration, and its energy is equal to

[0003] Graphene has attracted extensive attention in recent years due to its excellent physical properties. Although the intrinsic thermal conductivity of graphene is high, its good mechanical flexibility and excellent electrical transport performance make it possible to be applied in the field of thermoelectricity. If the thermal conductivity of graphene can be effectively reduced without reducing the electrical transport performance, the thermoelectric performance of graphene can be greatly improved. In addition, based on its high thermal conductivity, graphene has been widely used in chip packaging, optoelectronic devices, supercomputers, thermal conductive silicone grease, nanofluids and composite materials for heat dissipation and enhanced thermal conductivity. However, due to various limitations in actual synthesis, many additional phonon scattering is introduced, and the added graphene sheets are not ideal for improving the thermal conductivity of the composite material. If the thermal conductivity can be further improved, it has important practical significance for the application of graphene in the field of heat dissipation. SUMMARY

[0004] In view of the above defects or improvement needs of the prior art, the present application provides a method for quantumizing and regulating thermal conductivity of a material, wherein the energy eigenvalue and the ground state energy of electrons of graphene material and the second or third derivative of the energy eigenvalue and the ground state energy with respect to atomic displacement are combined based on the characteristics of the graphene material and the thermal conductivity regulation process, the contribution value of each eigenmode to the thermal conductivity or the mode thermal conductivity is calculated, the material thermal conductivity contribution spectrum is obtained according to the contribution value of each eigenmode to the thermal conductivity or the mode thermal conductivity, the phonon eigenmode that dominates the thermal conductivity of the material is selected, the resonance absorption of terahertz pulse is used to excite the phonon of a specific frequency, so as to increase the energy of the phonon of the specific frequency and convert it into the phonon eigenmode that dominates the thermal conductivity of the material, and then the number of the phonon eigenmode that dominates the thermal conductivity of the material is changed to change and regulate the thermal conductivity of the material. The present application regulates in situ, changes the thermal conductivity of the material without affecting other mechanical properties, is simple to control, has no complex process procedures and high synthesis cost, and has fast response. The excitation of terahertz pulse to the specific phonon is very fast.

[0005] To achieve the above object, the present application provides a method for quantumizing and regulating thermal conductivity of a material, characterized in that the method comprises the following steps:

[0006] Step one, obtaining the second or third derivative of the energy eigenvalue and the ground state energy of electrons with respect to atomic displacement;

[0007] Step two, if the second derivative is obtained, the phonon frequency and the eigen vector of the material are calculated according to the second derivative, and then the non-equilibrium molecular dynamics simulation is performed according to the phonon frequency and the eigen vector, so as to obtain the stable value of the heat flow contributed by each phonon eigenmode, and then the contribution value of each eigenmode to the thermal conductivity is calculated according to the Fourier heat conduction law;

[0008] Step three, if the third derivative is obtained, the phonon scattering matrix is obtained according to the third derivative, the phonon line width is calculated according to the wave vector, the relaxation time is calculated according to the phonon line width, and the phonon Boltzmann transport equation is solved under the assumption of the relaxation time, so as to obtain the mode thermal conductivity and the lattice thermal conductivity;

[0009] Step four, the material thermal conductivity contribution spectrum is obtained according to the contribution value of each eigenmode to the thermal conductivity or the mode thermal conductivity, and the phonon eigenmode that dominates the thermal conductivity of the material is selected;

[0010] Step five, the resonance absorption of terahertz pulse is used to excite the phonon of a specific frequency, so as to increase the energy of the phonon of the specific frequency and convert it into the phonon eigenmode that dominates the thermal conductivity of the material, and then the number of the phonon eigenmode that dominates the thermal conductivity of the material is changed to change and regulate the thermal conductivity of the material.

[0011] As a further preferred, in step one, based on the atomic structure parameters and the electron potential of the lattice of the material, the energy eigenvalue E of the electron is obtained by solving the Schrodinger equation based on the plane wave pseudo-potential method, and the second-order derivative or the third-order derivative of the ground state energy of the material with respect to the atomic displacement is obtained according to the perturbation theory.

[0012] As a further preferred, the second-order derivative calculation formula is as follows:

[0013]

[0014] The third-order derivative calculation formula is as follows:

[0015]

[0016] In the formula, m, V, r, ψ and E represent the reduced Planck constant, the electron mass, the electron potential, the spatial position, the electron wave function and the energy, respectively, Φ represents the force constant matrix, the subscripts α, β and γ represent the components in the x, y and z directions, j, j' and j" represent the atoms in the primitive cell, l, l' and l" represent different primitive cells, and u represents the atomic displacement, represents a small amount of change in the x-direction displacement, represents a small amount of change in the y-direction displacement, represents a small amount of change in the z-direction displacement.

[0017] As a further preferred, in step two, if the second-order derivative is obtained, the dynamic matrix is obtained by combining the second-order force constant matrix with the allowed wave vector of the material system, and then the phonon frequency and the eigenvector are obtained, and the non-equilibrium molecular dynamics simulation is performed combined with the eigenvector information, and after a period of evolution, the steady value of the heat flow contributed by each eigenmode is obtained according to the recorded velocity, total energy and stress tensor of each atom in the control volume, and then the contribution value of each eigenmode to the thermal conductivity is calculated according to the Fourier heat conduction law.

[0018] As a further preferred, the contribution value calculation model of each eigenmode to the thermal conductivity is as follows:

[0019]

[0020] In the formula, κ(k, v) is the eigenmode thermal conductivity, Q(k, v) is the eigenmode heat flow, V c is the volume of graphene, is the temperature gradient.

[0021] As a further preferred, in step three, if the three-order derivative is obtained, the three-order force constant matrix is used to obtain the scattering matrix, and then the phonon linewidth is obtained according to the wave vector, and the relaxation time is further calculated, and the phonon Boltzmann transport equation is solved under the approximation assumption of the relaxation time to obtain the lattice thermal conductivity:

[0022]

[0023] In the formula, κ is the thermal conductivity, c(k, v) is the eigenmode heat capacity, is the square of the group velocity, and τ(k, v) is the relaxation time.

[0024] As a further preferred, in step five, the motion speed of the atom is modified to achieve the regulation effect of the phonon eigenmode energy:

[0025]

[0026] In the formula, v, m, and e respectively represent the atomic speed, the atomic mass, the normal speed and the eigen vector, the subscripts i and n respectively represent different atoms and different phonon eigenmodes, the lower case a and o respectively represent after and before the modification, and the constant D represents the multiple of the increase or decrease of the phonon eigenmode energy before and after the modification.

[0027] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0028] 1. The present application is simple to control, and has no complex process procedures and high synthesis cost.

[0029] 2. The present application uses in-situ regulation, which can change the thermal conductivity of the material without affecting other mechanical properties.

[0030] 3. The present application responds quickly, and the terahertz pulse is very fast for the excitation of specific phonons.

[0031] 4. The present application is flexible to regulate, and the thermal conductivity can be greatly changed by increasing the number of different frequency phonons. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a flowchart of a method for quantum regulation of thermal conductivity of a material according to a preferred embodiment of the present application;

[0033] Figure 2 is a control flowchart of a method for quantum regulation of thermal conductivity of a material according to a preferred embodiment of the present application;

[0034] Figure 3 is a schematic diagram of the results of the regulation and improvement of the thermal conductivity of graphene using molecular dynamics simulation calculation;

[0035] Figure 4 is a schematic diagram of the result of the regulation of the thermal conductivity of graphene using first-principle simulation calculation;

[0036] Figure 5 is a schematic diagram of the result of the regulation of the thermal conductivity of graphene using molecular dynamics simulation calculation;

[0037] Figure 6 is a schematic diagram of the result of the regulation of the thermal conductivity of graphene using first-principle simulation calculation.

[0038] The above Figures 3 to 6 In the above, the horizontal coordinate Frequency [THz] is frequency; the vertical coordinate K [W / (m·K)] is intrinsic mode thermal conductivity, and more specifically, intrinsic is intrinsic mode thermal conductivity, modulated is regulated intrinsic mode thermal conductivity, ZA-intrinsic is the intrinsic mode thermal conductivity of ZA branch phonon, TA-intrinsic is the intrinsic mode thermal conductivity of TA branch phonon, LA-intrinsic is the intrinsic mode thermal conductivity of LA branch phonon, ZA-modulated is the regulated intrinsic mode thermal conductivity of ZA branch phonon, TA-modulated is the regulated intrinsic mode thermal conductivity of TA branch phonon, and LA-modulated is the regulated intrinsic mode thermal conductivity of LA branch phonon. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0040] As Figure 1 and Figure 2 shown, the method for regulating the thermal conductivity of the material provided by the embodiment of the present application comprises the following steps:

[0041] Step one, first determine the atomic structure parameters of the material, such as the spacing between carbon atoms in graphene material, the cutoff energy of the electron plane wave in graphene, etc. And use experimental measurement to measure the actual phonon dispersion relation of graphene material. In this application, graphene material is taken as an example, and the thermal conductivity of graphene is regulated according to the needs to meet different needs.

[0042] The energy eigenvalue of the atoms of the graphene material and the second derivative or the third derivative of the ground state energy with respect to the atomic displacement are obtained. In this step, the energy eigenvalue E of the electron is obtained by solving the Schrodinger equation based on the plane wave pseudo-potential method according to the atomic structure parameters and the electron potential of the material lattice, and the second derivative or the third derivative of the ground state energy of the material with respect to the atomic displacement is obtained according to the perturbation theory.

[0043] The second derivative calculation formula is as follows:

[0044]

[0045] The third derivative calculation formula is as follows:

[0046]

[0047] In the formula, E represents energy, Φ() represents a force constant matrix, subscripts α, β and γ represent x, y and z direction components, j, j' and j" represent atoms in a primitive cell, l, l' and l" represent different primitive cells, u represents atomic displacement, represents a small amount of x direction displacement change, represents a small amount of y direction displacement change, represents a small amount of y direction displacement change.

[0048] More specifically, in the present application, the Schrodinger equation is solved based on the plane wave pseudo-potential method:

[0049]

[0050] In the formula, m, r and E respectively represent the reduced Planck constant, the electron mass, the spatial position and the energy, is the Laplace operator, V(r) is the electron potential, and ψ(r) is the electron wave function.

[0051] In this step, the second force constant matrix is obtained according to the second derivative, and the theoretical phonon dispersion relationship is obtained. The theoretical phonon dispersion relationship is compared with the actual phonon dispersion relationship. If the theoretical phonon dispersion relationship is consistent with the actual phonon dispersion relationship, it is determined that the atomic structure parameters of the material are correctly selected, and step two is entered. Otherwise, the atomic structure parameters of the material are adjusted until the theoretical phonon dispersion relationship is consistent with the actual phonon dispersion relationship.

[0052] In step two, if the second derivative is obtained, the phonon frequency and the eigen vector of the material are obtained according to the second derivative, and the non-equilibrium molecular dynamics simulation is performed according to the phonon frequency and the eigen vector, so as to obtain the stable value of the heat flow contributed by each phonon eigen mode. According to the Fourier heat conduction law, the contribution value of each eigen mode to the thermal conductivity is calculated. More specifically, the dynamic matrix is obtained by combining the second force constant matrix and the allowed wave vector of the system:

[0053]

[0054] In the above formula, D αβ (jj′, k) is the kinetic matrix element, k is the wave vector, m j is the mass of the jth atom in the primitive cell, m j′ is the mass of the jth atom in the primitive cell, i is the imaginary unit, r(j′l′) is the position of the jth atom in the l′th primitive cell, and r(jl) is the position of the jth atom in the l′th primitive cell.

[0055] Further, the phonon frequency and eigenvector are obtained:

[0056] ω 2 (k, v) e(k, v) = D(k) · e(k, v)

[0057] In the above formula, ω is the angular frequency, v represents the phonon polarization, ω 2 (k, v) is the square of the eigenmode frequency, e(k, v) is the eigenvector, and D(k) is the kinetic matrix.

[0058] In combination with the eigenvector information, non-equilibrium molecular dynamics simulation is performed, and after a period of evolution, the heat flow contributed by each eigenmode can be obtained according to the recorded velocity, total energy, and stress tensor of each atom in the control volume:

[0059]

[0060] In the above formula, Q(k, v) is the eigenmode heat flow, N is the number of atoms in the simulation, E(jl, t) is the total energy of the jth atom in the l′th primitive cell at time t, e(j, k, v) is the jth component of the eigenvector, exp[ikr(jl)] is the phase factor, is the normal velocity of the eigenmode, and S(jl, t) is the stress tensor of the jth atom in the l′th primitive cell at time t.

[0061] where the normal velocity calculation model of the phonon is as follows:

[0062]

[0063] In the above formula, is the normal velocity of the eigenmode, e * (j, k, v) is the complex conjugate of the jth component of the eigenvector, is the velocity of the jth atom in the l′th primitive cell at time t.

[0064] According to the Fourier heat conduction law, the contribution value of each eigenmode to the thermal conductivity is calculated:

[0065]

[0066] In the above formula, k(k, v) is intrinsic mode thermal conductivity, Q(k, v) is intrinsic mode heat flow, V c is the volume of graphene, is the temperature gradient.

[0067] Step three, if the third derivative is obtained, the phonon scattering matrix is obtained according to the third derivative, the phonon line width is obtained according to the wave vector, the relaxation time is calculated according to the phonon line width, the phonon Boltzmann transport equation is solved under the relaxation time approximation, and thus the lattice thermal conductivity is obtained.

[0068] More specifically, the scattering matrix is obtained by using the third order force constant matrix:

[0069]

[0070] In the above formula, Φ λλ′λ″ is the scattering matrix, λ, λ' and λ'' represent the phonon wavelength, k, k' and k'' represent different atoms, q, q' and q'' represent the phonon wave vector, W α (k, λ) is the kth α component of the phonon polarization vector with wavelength λ, W β (k', λ') is the kth α component of the phonon polarization vector with wavelength λ, W γ (k'', λ'') is the kth α component of the phonon polarization vector with wavelength λ, m k is the mass of the kth atom, is the force constant matrix element, e iq′·[r(l′k′)-r(0k)] is the phase difference of the vibration eigenmode of the k' th atom in the l' th unit cell with respect to the kth atom in the 0th unit cell with wave vector q', e iq″·[r(l″k″)-r(0k)] is the phase difference of the vibration eigenmode of the k''th atom in the l''th unit cell with respect to the kth atom in the 0th unit cell with wave vector q'', e i(q+q′+q″)·r(0k) is the phase superposition of the vibration eigenmode of the kth atom in the 0th unit cell with wave vectors q, q' and q'', and Δ(q+q'+q'') is the delta function, which is 1 only when q+q'+q'' is the reciprocal lattice vector, and 0 otherwise.

[0071] The phonon line width is obtained according to the wave vector:

[0072]

[0073] In the above formula, Γ λ (ω) is the phonon line width with wavelength λ and frequency ω, n λ′ is the phonon occupation number with wavelength λ' at equilibrium, and δ is the delta function.

[0074] Further calculate the relaxation time:

[0075]

[0076] In the above equation, τ λ is the phonon lifetime for wavelength λ, Γ λ (ω λ ) is the phonon linewidth.

[0077] Solve the phonon Boltzmann transport equation under the relaxation time approximation hypothesis:

[0078]

[0079] In the above equation, u p is the phonon group velocity, is the gradient of the phonon distribution function, f p is the distribution function of the phonon, and s represents the steady state.

[0080] Get the mode thermal conductivity and the lattice thermal conductivity:

[0081]

[0082] In the above equation, c(k, v) is the eigenmode heat capacity, is the square of the group velocity, τ(k, v) is the relaxation time, and the summation symbol inside is the single mode thermal conductivity, and the summation is the summation over all modes.

[0083] Step four, according to the numerical value of the contribution of each eigenmode to the thermal conductivity or the mode thermal conductivity, get the material thermal conductivity contribution spectrum, and select the phonon eigenmode that dominates the material thermal conductivity. In this step, the thermal conductivity contribution spectrum can be obtained according to the mode thermal conductivity calculated in the previous steps, and further normalization of the thermal conductivity contribution spectrum can get the specific proportion of the contribution of each eigenmode to the total thermal conductivity, and according to the contribution proportion of each eigenmode, select the dominant part of the phonon eigenmode.

[0084] Step five, the resonance absorption of terahertz pulse excitation of specific frequency phonon is used to increase the energy of the specific frequency phonon, so as to change the number of phonon eigenmodes of the dominant material thermal conductivity, so as to change the thermal conductivity of the material. In this step, the interaction of terahertz pulse and material lattice will cause the resonance absorption of specific frequency phonon (i.e. the terahertz excitation pulse with a repetition frequency of 1 kHz is generated by optical rectification, which excites the specific frequency optical phonon in the MAPbI3 film; the intensity of the terahertz excitation pulse is controlled by a pair of wire grid polarizers working in the terahertz frequency range), so as to increase the energy of this part of phonon eigenmodes, and then change the number of this part of phonon eigenmodes in the system. In the simulation, the similar regulation effect can be achieved by modifying the motion speed of the atom:

[0085]

[0086] In the above formula, v, m, and e respectively represent the atomic speed, atomic mass, normal velocity and eigen vector, the subscripts i and n respectively represent different atoms and different phonon eigenmodes, and the subscripts a and o respectively represent after modification and before modification, and the constant D represents the multiple of the increase or decrease of the phonon eigenmode energy before and after modification.

[0087] In this step, after the regulation is completed, the thermal conductivity of the regulated material needs to be detected. If the thermal conductivity of the material is increased or decreased to the set value, the regulation is completed, otherwise the resonance absorption of terahertz pulse excitation of specific frequency phonon is continued.

[0088] The thermal conductivity of the material is determined by the intrinsic phonon scattering property. Changing the number of part of phonon will affect the scattering process in the system, so that the number of regulated phonon eigenmodes is changed, and the thermal conductivity of the material is changed, so that the effective thermal conductivity is improved or reduced.

[0089] In this application, the above thermal conductivity calculation method is also verified by experimental test method. In the experiment, the vibration spectrum of the phonon can be measured by inelastic neutron scattering first. The scattering process follows the conservation of energy and momentum. In the experiment, the energy difference before and after the neutron scattering is measured, and the energy information of the phonon can be accurately given according to the energy conservation:

[0090]

[0091] According to the geometric relationship between the directions of incident and scattered neutrons, the momentum conservation is based on:

[0092]

[0093] The wave vector of the phonon is determined, and thus the vibration spectrum of the phonon is obtained, containing intrinsic frequency and group velocity and other information; the phonon linewidth can also be calculated, and the corresponding relaxation time is calculated by using the above relaxation time calculation model, and then the thermal conductivity of each intrinsic phonon mode in the material is statistically obtained:

[0094]

[0095]

[0096] Wherein, p', p, M n And p', p, M and k respectively represent the momentum of the incident neutron, the momentum of the outgoing neutron, the mass of the neutron and the reciprocal lattice vector.

[0097] The graphene thermal conductivity regulation and improvement results calculated by the molecular dynamics simulation of the application are shown as follows: Figure 3 Figure 3 The molecular dynamics simulation results are shown, in the simulation box with a size of 2.46*2.13 nm, the width direction is set as a periodic boundary, and the length direction is a fixed boundary, the movement speed of the atoms in the correction box is corrected, by increasing the phonon energy of 8.5-9.5 THz frequency by 30 times, the thermal conductivity of each intrinsic mode changes, and the total thermal conductivity increases from 59.0 W / (m*K) to 68.3 W / (m*K), increasing by 15.8%. This is mainly caused by the increase of the intrinsic mode thermal conductivity contribution below 20 THz.

[0098] The graphene thermal conductivity regulation and improvement results calculated by the first principle simulation of the application are shown as follows: Figure 4 Figure 4 The first principle simulation results are shown, under the condition of considering 9 near-neighbor atoms, and all directions are periodic boundaries, 8*8 supercell, the original distribution size of the intrinsic mode is corrected, by expanding the distribution of ZA phonon with a frequency of 13.93-13.94 THz to 30 times of the original (equivalent to increasing the energy by 30 times), the thermal conductivity of each intrinsic mode changes, and the total thermal conductivity increases from 3200 W / (m*K) to 3426 W / (m*K), increasing by 7.1%. This is mainly caused by the increase of the intrinsic mode thermal conductivity contribution below 15 THz.

[0099] The graphene thermal conductivity regulation and reduction results calculated by the molecular dynamics simulation of the application are shown as follows: Figure 5 Figure 5 ​​​The molecular dynamics simulation results are shown, in the simulation box with a size of 2.46*2.13 nm, the width direction is set as a periodic boundary, the length direction is a fixed boundary, the movement speed of atoms in the correction box is corrected, by increasing the phonon energy of 21.5-22.5 THz frequency by 30 times, the thermal conductivity of each eigenmode changes, the total thermal conductivity is reduced from 59.0 W / (m*K) to 51.5 W / (m*K), and the reduction is 12.7%. This is mainly due to the decrease of the eigenmode thermal conductivity contribution below 15 THz.

[0100] The present application uses the first principle simulation calculation of graphene thermal conductivity regulation and reduction results, as shown in Figure 6 Figure 6 The first principle simulation results are shown, under the condition of considering 9 near-neighbor atoms, and all directions are periodic boundaries, 8*8 supercell, the original distribution size of the eigenmode is corrected, by expanding the TA branch phonon distribution of 18.1-18.2 THz frequency to 100 times of the original (equivalent to increasing the energy by 100 times), the thermal conductivity of each eigenmode changes, the total thermal conductivity is reduced from 3200 W / (m*K) to 630 W / (m*K), and the reduction is 80.3%. This is mainly due to the decrease of the eigenmode thermal conductivity contribution in almost the whole frequency band.

[0101] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for quantizing the thermal conductivity of a material, characterized in that: The following steps are involved: Step 1: Obtain the energy eigenvalues ​​and second-order or third-order derivatives of the ground-state energy of electrons in the material with respect to atomic displacement; Step 2: If the second-order derivative is obtained, the material phonon frequency and eigenvector are obtained based on the second-order derivative, and non-equilibrium molecular dynamics simulation is performed based on this to obtain the stable value of the heat flow contributed by each phonon eigenmode. Then, according to Fourier's law of heat conduction, the contribution of each eigenmode to the thermal conductivity is calculated; Step 3: If the third-order derivative is obtained, the phonon scattering matrix is ​​obtained according to the third-order derivative, and the phonon linewidth is obtained according to the wave vector. The relaxation time is calculated according to the phonon linewidth, and the phonon Boltzmann transport equation is solved under the relaxation time approximation assumption to obtain the mode thermal conductivity and the lattice thermal conductivity; Step 4: Obtain the material thermal conductivity contribution spectrum based on the contribution value of each eigenmode to the thermal conductivity or the mode thermal conductivity, and select the phonon eigenmode that dominates the thermal conductivity of the material; Step five: Use terahertz pulses to stimulate the resonant absorption of phonons of a specific frequency, thereby increasing the energy of the phonons of the specific frequency and converting them into phonon eigenmodes that dominate the thermal conductivity of the material, thereby changing the number of phonon eigenmodes that dominate the thermal conductivity of the material to change and regulate the thermal conductivity of the material.

2. The method for quantizing and controlling the thermal conductivity of a material according to claim 1, wherein: In step 1, the Schrödinger equation is solved based on the plane wave pseudopotential method according to the atomic structure parameters and electron potential of the material lattice to obtain the energy eigenvalue E of the electron. The second or third derivative of the ground state energy of the material with respect to the atomic displacement is obtained according to the perturbation theory.

3. The method for quantizing and controlling the thermal conductivity of a material according to claim 2, wherein: The second-order derivative calculation formula is as follows: The third-order derivative calculation formula is as follows: Where, m, V, r, ψ and E represent the reduced Planck constant, electron mass, electron potential, spatial position, electron wave function and energy respectively, Φ represents the force constant matrix, subscripts α, β and γ represent the components in the x, y and z directions, j, j′ and j″ represent atoms in the unit cell, l, l′ and l″ represent different unit cells, u represents the atomic displacement, represents a small amount of displacement change in the x direction, represents a small amount of displacement change in the y direction, A small amount representing the change in displacement in the z direction.

4. The method for quantizing and controlling the thermal conductivity of a material according to claim 1, wherein: In step 2, if the second-order derivative is obtained, the dynamic matrix is ​​obtained by combining the second-order force constant matrix with the wave vector allowed by the material system, and then the phonon frequency and eigenvector are obtained. Combined with the eigenvector information, non-equilibrium molecular dynamics simulation is performed. After a period of evolution, the heat flow stability value contributed by each eigenmode can be obtained based on the recorded velocity, total energy and stress tensor of each atom in the control volume. Then, according to Fourier's law of heat conduction, the contribution value of each eigenmode to the thermal conductivity is calculated.

5. The method for quantizing and controlling thermal conductivity of a material according to claim 1, wherein: The numerical calculation model of the contribution of each eigenmode to thermal conductivity is as follows: Where κ(k,v) is the eigenmode thermal conductivity, Q(k,v) is the eigenmode heat flux, and V c is the volume of graphene, is the temperature gradient.

6. The method for quantizing and controlling thermal conductivity of a material according to claim 1, wherein: In step 3, if the third-order derivative is obtained, the third-order force constant matrix is ​​used to obtain the scattering matrix, and then the phonon linewidth is calculated based on the wave vector. The relaxation time is further calculated, and the phonon Boltzmann transport equation is solved under the relaxation time approximation to obtain the mode thermal conductivity and lattice thermal conductivity: Where κ is the thermal conductivity, c(k,v) is the intrinsic mode heat capacity, is the square of the group velocity, τ(k,v) is the relaxation time, the summation symbol is the thermal conductivity of a single mode, and the sum is the sum of all modes.

7. The method for quantizing and controlling thermal conductivity of a material according to claim 1, wherein: In step 5, the energy of the phonon eigenmode is controlled by modifying the atomic velocity: In the formula, v, m, and e represent atomic velocity, atomic mass, normal velocity and eigenvector respectively. Subscripts i and n represent different atoms and different phonon eigenmodes respectively. In the table below, a and o represent the correction and before correction respectively. The constant D represents the multiple of the increase or decrease in the energy of the phonon eigenmode before and after correction.

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