A simple equation of state （EOS） in wide ranges of pressure and temperature is constructed within the MieGruneisen Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter co...A simple equation of state （EOS） in wide ranges of pressure and temperature is constructed within the MieGruneisen Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter cold energy expression to represent the static EOS term, which can correctly produce cohesive energy without any spurious oscillations in the extreme compression and expansion regions, We developed a Pade approximation-based analytic Debye quasiharmonic model with high accuracy which improves the performance of EOS in the low temperature region. The anharmonic effect is taken into account by using a semi-empirical approach. Its reasonability is verified by the fact that the total thermal pressure tends to the lowest-order anharmonic expansion in the literature at low temperature, and tends to ideal-gas limitation at high temperature, which is physically correct. Besides, based on this approach, the anharmonic thermal pressure can be expressed in the Griineisen form, which is convenient for applications. The proposed EOS is used to study the thermodynamic properties of MgO including static and shock compression conditions, and the results are very satisfactory as compared with the experimental data.展开更多
It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in ...It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in predict- ing the densities for the α phase crystalline hexahydro-1,3,5-trinitro-l,3,5-triazine （RDX）, and derivation of its high-fidelity Hugoniot locus and Mie-Grfineisen equation of state covering a very wide range of pressures and temperatures. This work can be used to efficiently and accurately predict the thermophysical properties of solid explosives over the pressures and temperatures to which they are subjected, which is a long-standing issue in the field of energetic materials.展开更多
Based on the scattering matrix approach.we systematically investigate the anharmonic effect of the pumped current in double-barrier strructures with adiabatic time-modulation of two sinusoidal AC driven potential he...Based on the scattering matrix approach.we systematically investigate the anharmonic effect of the pumped current in double-barrier strructures with adiabatic time-modulation of two sinusoidal AC driven potential heights. The pumped currem as a functionof the pha.se difference bet ween the two driven potentials looks like to be sinusoidal, but actually it contains sine functions of double and more phase difference, it is found that this kind of anharmonic effect of the pumped current is determined combinedly by the Berry curvature and parameter va.riation loop trajectory. Therefore small ratio of the driving amplitude and the static amplitude is not necessary for harmonic pattern in the pmnped era＇rent, to dominate for smooth Berry curvatureon the surface within the parameter variation loop.展开更多
The importance of anharmonic effect in dissociation of molecular systems especially clusters has been noted.In this paper,we shall study the effect of coupled anharmonic oscillator of the standard bilinear form(SBF)Mo...The importance of anharmonic effect in dissociation of molecular systems especially clusters has been noted.In this paper,we shall study the effect of coupled anharmonic oscillator of the standard bilinear form(SBF)Morse oscillator(MO)potential on unimolecular reaction.We shall use the systematic theoretical approach,YL method,proposed by Yao and Lin(YAO L,et.al.J Phys Chem A,2007,111(29):6722-6729),which can evaluate anharmonic effects on the rate constants based on the transition state theory.In treating the anharmonic effect with the Morse oscillator potential on unimolecular reactions under collision-free conditions by using the RRKM(Rice-Ramsperger-Kassel-Marcus)theory,the in-verse Laplace transformation of the partition functions was used to obtain the total amount of state and density of state by using the first-order and the second-order approximations of the saddle-point method.To demonstrate the anharmonic effect of the SBF Morse model,we choose some model systems and a real reaction as examples.展开更多
Phonon quasiparticles and their anharmonic interactions govern heat transport in insulators.Accurate characterization of phonon frequencies and linewidths,especially beyond the quasiparticle approximation,is essential...Phonon quasiparticles and their anharmonic interactions govern heat transport in insulators.Accurate characterization of phonon frequencies and linewidths,especially beyond the quasiparticle approximation,is essential for understanding anharmonic effects and lattice thermal conductivity.Here,we investigate the anharmonic lattice dynamics and phonon transport in crystalline copper halides CuBiI_(4) using the self-consistent phonon theory,combined with the Wigner transport formalism and the quasi-harmonic Green–Kubo method.Results show that the three-phonon bubble self-energy substantially renormalizes the phonon dispersion,inducing strong modedependent broadening.Depending on the strength of the anharmonic scattering,phonons exhibit particle-like,wave-like,or overdamped transport characteristics,with broadened states contributing additional coherent thermal transport channels.We establish a consistent description of the overdamped phonon self-energy and advance the microscopic understanding of the strongly anharmonic phonon thermal transport in CuBiI_(4).Overdamped phonon modes significantly hinder the lattice thermal transport by reducing phonon lifetimes.However,the still well-defined phonon dispersions mitigate carrier scattering induced by the local structural disorder.Anisotropic electrical transport properties are obtained by considering polar and non-polar electroacoustic coupling and ionized impurity scattering mechanisms.Upon electron doping,the thermoelectric figure of merit of n-type CuBiI_(4) reaches 2.25 at 800 K.展开更多
We compare the direct free energy interpolation(DFEI) method and the quasi-harmonic approximation(QHA) in calculating of the equation of states and thermodynamic properties of prototype Al. The Gibbs free energy of Al...We compare the direct free energy interpolation(DFEI) method and the quasi-harmonic approximation(QHA) in calculating of the equation of states and thermodynamic properties of prototype Al. The Gibbs free energy of Al is calculated using the DFEI method based on the high-temperature phonon density of states reduced from classical molecular dynamics simulations. Then, we reproduce the thermal expansion coefficients, the specific heat, the isothermal bulk modulus of Al accurately. By comparing the results from the DFEI method and the QHA, we find that the DFEI method is indeed more accurate in calculating anharmonic properties than the QHA.展开更多
Quantum nuclear effects and anharmonicity impact a wide range of functional materials and their properties.One of the most powerful techniques to model these effects is the Stochastic Self-Consistent Harmonic Approxim...Quantum nuclear effects and anharmonicity impact a wide range of functional materials and their properties.One of the most powerful techniques to model these effects is the Stochastic Self-Consistent Harmonic Approximation(SSCHA).Unfortunately,the SSCHA is extremely computationally expensive,prohibiting its routine use.We propose a protocol that pairs machine learning interatomic potentials,which can be tailored for the system at hand via active learning,with the SSCHA.Our method leverages an upscaling procedure that allows for the treatment of supercells of up to thousands of atoms with practically minimal computational effort.The protocol is applied to PdCuH_(x)(x=0−2)compounds,chosen because previous experimental studies have reported superconducting critical temperatures,Tcs,as high as 17 K at ambient pressures in an unknown hydrogenated PdCu phase.We identify a P4/mmm PdCuH_(2)structure,which is shown to be dynamically stable only upon the inclusion of quantum fluctuations,as being a key contributor to the measured superconductivity.For this system,our methodology is able to reduce the computational expense for the SSCHA calculations by~96%.The proposed protocol opens the door towards the routine inclusion of quantum nuclear motion and anharmonicity in materials discovery.展开更多
In this paper,Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition（LPMOCVD） are investigated.We compare the crystal qualities and study the ...In this paper,Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition（LPMOCVD） are investigated.We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K.The temperature-dependences of GaN phonon modes（A1（TO）,E2（high）,and E1（TO）） and the linewidths of E2（high） phonon peak are studied.The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range,and the relationship can be fitted to the pseudo-Voigt function.From analytic results we find a critical temperature existing in the relationship,which can characterize the anharmonic effects of a-plane GaN in different temperature ranges.In the range of higher temperature,the relationship exhibits an approximately linear behavior,which is consistent with the analyzed results theoretically.展开更多
Anti-Stokes/Stokes Raman peak intensity ratio was used to infer sample temperatures,but the influence factors of system correction factors were not clear.Non-contact in-situ anti-Stokes/Stokes temperature calibration ...Anti-Stokes/Stokes Raman peak intensity ratio was used to infer sample temperatures,but the influence factors of system correction factors were not clear.Non-contact in-situ anti-Stokes/Stokes temperature calibration was carried out for up to 1500 K based on six different samples under two excitation light sources(±50 K within 1000 K,±100 K above1000 K),and the system correction factorγwas systematically investigated.The results show that the correction factorγof anti-Stokes/Stokes thermometry is affected by the wavelength of the excitation light source,Raman mode peak position,temperature measurement region and other factors.The anti-Stokes/Stokes thermometry was applied to the laser-heating diamond anvil cell(LHDAC)experiment to investigate the anharmonic effect of h BN under high temperature and high pressure.It is concluded that the strong anharmonic effect caused by phonon scattering at low pressure gradually changes into the predominance of localized molecular lattice thermal expansion at high pressure.展开更多
基金Project supported by the Joint Fund of National Natural Science Foundation of China and China Academy of Engineering Physics(Grant No. 10876008)
文摘A simple equation of state （EOS） in wide ranges of pressure and temperature is constructed within the MieGruneisen Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter cold energy expression to represent the static EOS term, which can correctly produce cohesive energy without any spurious oscillations in the extreme compression and expansion regions, We developed a Pade approximation-based analytic Debye quasiharmonic model with high accuracy which improves the performance of EOS in the low temperature region. The anharmonic effect is taken into account by using a semi-empirical approach. Its reasonability is verified by the fact that the total thermal pressure tends to the lowest-order anharmonic expansion in the literature at low temperature, and tends to ideal-gas limitation at high temperature, which is physically correct. Besides, based on this approach, the anharmonic thermal pressure can be expressed in the Griineisen form, which is convenient for applications. The proposed EOS is used to study the thermodynamic properties of MgO including static and shock compression conditions, and the results are very satisfactory as compared with the experimental data.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11372053,11402031,11221202 and 11172044the Opening Project of the State Key Laboratory of Explosion Science and Technology under Grant No KFJJ14-06M
文摘It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in predict- ing the densities for the α phase crystalline hexahydro-1,3,5-trinitro-l,3,5-triazine （RDX）, and derivation of its high-fidelity Hugoniot locus and Mie-Grfineisen equation of state covering a very wide range of pressures and temperatures. This work can be used to efficiently and accurately predict the thermophysical properties of solid explosives over the pressures and temperatures to which they are subjected, which is a long-standing issue in the field of energetic materials.
基金This project was supported by the Na- tional Natural Science Foundation of China （Grant No. 11004063） and the Fundamental Research Funds for the Central Universities, SCUT （Grant No. 2012ZZ0076）.
文摘Based on the scattering matrix approach.we systematically investigate the anharmonic effect of the pumped current in double-barrier strructures with adiabatic time-modulation of two sinusoidal AC driven potential heights. The pumped currem as a functionof the pha.se difference bet ween the two driven potentials looks like to be sinusoidal, but actually it contains sine functions of double and more phase difference, it is found that this kind of anharmonic effect of the pumped current is determined combinedly by the Berry curvature and parameter va.riation loop trajectory. Therefore small ratio of the driving amplitude and the static amplitude is not necessary for harmonic pattern in the pmnped era＇rent, to dominate for smooth Berry curvatureon the surface within the parameter variation loop.
基金Supported by the National Natural Science Foundation of China(Grant No.10704012)NSC(Taiwan),Academia Sinica,and the Natural Science Foundation of Liaoning Province(Grant No.2006Z064)
文摘The importance of anharmonic effect in dissociation of molecular systems especially clusters has been noted.In this paper,we shall study the effect of coupled anharmonic oscillator of the standard bilinear form(SBF)Morse oscillator(MO)potential on unimolecular reaction.We shall use the systematic theoretical approach,YL method,proposed by Yao and Lin(YAO L,et.al.J Phys Chem A,2007,111(29):6722-6729),which can evaluate anharmonic effects on the rate constants based on the transition state theory.In treating the anharmonic effect with the Morse oscillator potential on unimolecular reactions under collision-free conditions by using the RRKM(Rice-Ramsperger-Kassel-Marcus)theory,the in-verse Laplace transformation of the partition functions was used to obtain the total amount of state and density of state by using the first-order and the second-order approximations of the saddle-point method.To demonstrate the anharmonic effect of the SBF Morse model,we choose some model systems and a real reaction as examples.
基金supported by the National Natural Science Foundation of China(Grant Nos.12574028,U2330104,and 12074381)Guang-dong Basic and Applied Basic Research Foundation(Grant No.2024A1515010484)。
文摘Phonon quasiparticles and their anharmonic interactions govern heat transport in insulators.Accurate characterization of phonon frequencies and linewidths,especially beyond the quasiparticle approximation,is essential for understanding anharmonic effects and lattice thermal conductivity.Here,we investigate the anharmonic lattice dynamics and phonon transport in crystalline copper halides CuBiI_(4) using the self-consistent phonon theory,combined with the Wigner transport formalism and the quasi-harmonic Green–Kubo method.Results show that the three-phonon bubble self-energy substantially renormalizes the phonon dispersion,inducing strong modedependent broadening.Depending on the strength of the anharmonic scattering,phonons exhibit particle-like,wave-like,or overdamped transport characteristics,with broadened states contributing additional coherent thermal transport channels.We establish a consistent description of the overdamped phonon self-energy and advance the microscopic understanding of the strongly anharmonic phonon thermal transport in CuBiI_(4).Overdamped phonon modes significantly hinder the lattice thermal transport by reducing phonon lifetimes.However,the still well-defined phonon dispersions mitigate carrier scattering induced by the local structural disorder.Anisotropic electrical transport properties are obtained by considering polar and non-polar electroacoustic coupling and ionized impurity scattering mechanisms.Upon electron doping,the thermoelectric figure of merit of n-type CuBiI_(4) reaches 2.25 at 800 K.
基金Supported by the National Natural Science Foundation of China under Grant No.41574076the Young Core Teacher Scheme of Henan Province under Grant No.2014GGJS-108the Fundamental and Cutting-edge Technology Research Program of Henan Province under Grant No.152300410218
文摘We compare the direct free energy interpolation(DFEI) method and the quasi-harmonic approximation(QHA) in calculating of the equation of states and thermodynamic properties of prototype Al. The Gibbs free energy of Al is calculated using the DFEI method based on the high-temperature phonon density of states reduced from classical molecular dynamics simulations. Then, we reproduce the thermal expansion coefficients, the specific heat, the isothermal bulk modulus of Al accurately. By comparing the results from the DFEI method and the QHA, we find that the DFEI method is indeed more accurate in calculating anharmonic properties than the QHA.
基金Funding for this research is provided by the National Science Foundation,under award DMR-2136038Calculations were performed at the Center for Computational Research at SUNY Buffalo(http://hdl.handle.net/10477/79221).
文摘Quantum nuclear effects and anharmonicity impact a wide range of functional materials and their properties.One of the most powerful techniques to model these effects is the Stochastic Self-Consistent Harmonic Approximation(SSCHA).Unfortunately,the SSCHA is extremely computationally expensive,prohibiting its routine use.We propose a protocol that pairs machine learning interatomic potentials,which can be tailored for the system at hand via active learning,with the SSCHA.Our method leverages an upscaling procedure that allows for the treatment of supercells of up to thousands of atoms with practically minimal computational effort.The protocol is applied to PdCuH_(x)(x=0−2)compounds,chosen because previous experimental studies have reported superconducting critical temperatures,Tcs,as high as 17 K at ambient pressures in an unknown hydrogenated PdCu phase.We identify a P4/mmm PdCuH_(2)structure,which is shown to be dynamically stable only upon the inclusion of quantum fluctuations,as being a key contributor to the measured superconductivity.For this system,our methodology is able to reduce the computational expense for the SSCHA calculations by~96%.The proposed protocol opens the door towards the routine inclusion of quantum nuclear motion and anharmonicity in materials discovery.
基金Project supported by the Fundamental Research Funds for the Central Universities,China (Grant No. K50511250002)the National Key Science & Technology Special Project,China (Grant No. 2008ZX01002-002)+1 种基金the Major Program and State Key Program of the National Natural Science Foundation of China (Grant Nos. 60890191 and 60736033)the Science Fund for Youths Scholars (Grant Nos. 61204006)
文摘In this paper,Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition（LPMOCVD） are investigated.We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K.The temperature-dependences of GaN phonon modes（A1（TO）,E2（high）,and E1（TO）） and the linewidths of E2（high） phonon peak are studied.The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range,and the relationship can be fitted to the pseudo-Voigt function.From analytic results we find a critical temperature existing in the relationship,which can characterize the anharmonic effects of a-plane GaN in different temperature ranges.In the range of higher temperature,the relationship exhibits an approximately linear behavior,which is consistent with the analyzed results theoretically.
基金financially supported by the National Natural Science Foundation of China(Grant No.U2030107)the Fundamental Research Funds for the Central Universities(Grant No.2020SCUNL107)。
文摘Anti-Stokes/Stokes Raman peak intensity ratio was used to infer sample temperatures,but the influence factors of system correction factors were not clear.Non-contact in-situ anti-Stokes/Stokes temperature calibration was carried out for up to 1500 K based on six different samples under two excitation light sources(±50 K within 1000 K,±100 K above1000 K),and the system correction factorγwas systematically investigated.The results show that the correction factorγof anti-Stokes/Stokes thermometry is affected by the wavelength of the excitation light source,Raman mode peak position,temperature measurement region and other factors.The anti-Stokes/Stokes thermometry was applied to the laser-heating diamond anvil cell(LHDAC)experiment to investigate the anharmonic effect of h BN under high temperature and high pressure.It is concluded that the strong anharmonic effect caused by phonon scattering at low pressure gradually changes into the predominance of localized molecular lattice thermal expansion at high pressure.
