The influence of pressure and temperature on the thermodynamic properties of MgCu intermetallic compound was investigated by quasi-harmonic Debye model approximation.The equation of state(EoS)parameters has performed ...The influence of pressure and temperature on the thermodynamic properties of MgCu intermetallic compound was investigated by quasi-harmonic Debye model approximation.The equation of state(EoS)parameters has performed using plane-wave pseudopotential(PW-PP)approach in the framework of the density functional theory(DFT)and the generalized gradient approximation(GGA)for the exchange-correlation functional.Our results agree well with other data of the literature.The finite temperature thermophysical properties under pressure up to 16 GPa and high temperature up to 800 K,respectively were determined.Our results of the thermophysical properties are also agree very well with other data of the literature,where for example at ambient temperature,the deviation between our obtained value(11.05 Cal mol^(−1)K^(−1))of C V,and the theoretical value(11.21 Cal mol^(−1)K^(−1))reported in the literature is only around 1.44%.The finite temperature thermophysical properties were found varied monotonically with either temperature or pressure.Compared with other materials previously studied,similar behaviors were observed.展开更多
In this paper, the lattice parameter and bulk modulus of lithium(Li) at different pressures and temperatures are calculated by using the density functional theory method within the generalized gradient approximation(G...In this paper, the lattice parameter and bulk modulus of lithium(Li) at different pressures and temperatures are calculated by using the density functional theory method within the generalized gradient approximation(GGA).Through the quasi-harmonic Debye model, the thermodynamic properties of Li are predicted. The dependences of the normalized primitive cell volume V/V0 on pressure P, the variation of the thermal expansion coefficient α with pressure P and temperature T, as well as the dependences of the heat capacity Cv on pressure P and temperature T are obtained systematically in the ranges of 0~100 GPa and 0~2 000 K.展开更多
Statistical expression of vapour pressure equations of metals is derived from the Debye model.The statistical distribution of T_(-p) ensemble is presented in an in-elab- orate mode and the partition function is define...Statistical expression of vapour pressure equations of metals is derived from the Debye model.The statistical distribution of T_(-p) ensemble is presented in an in-elab- orate mode and the partition function is defined.The vapour pressure of eleven metals have been calculated with the Debye equation and compared with those given by the E- instein equation and empirical equation.Comparison of results of calculation from dif- ferent methods show their evident accordance within the same orders of magnitude.展开更多
The thermodynamic properties of Mg Ca Si and its mother phase Ca2 Si are comparatively investigated from ab initio calculations and quasi-harmonic Debye-Grüneisen model. At 0 K, Mg Ca Si is more thermodynamically...The thermodynamic properties of Mg Ca Si and its mother phase Ca2 Si are comparatively investigated from ab initio calculations and quasi-harmonic Debye-Grüneisen model. At 0 K, Mg Ca Si is more thermodynamically stable. Under high temperature, the advantage of higher thermodynamically stability of Mg Ca Si is reduced, originating from the less negative entropy contribution because the thermodynamic entropy of Mg Ca Si increases more slowly with temperature and the entropy values are slightly smaller.With increasing temperature, the anti-softening ability for Mg Ca Si is slightly smaller due to the slightly faster decrease trend of bulk modulus than that of Ca2 Si, although the bulk modulus of Mg Ca Si is higher in the whole temperature range considered. The thermal expansion behaviors of both Mg Ca Si and Ca_(2)Si exhibit similar increase trend, although thermal expansion coefficient of MgCaSi is slightly lower and the increases is slightly slower at lower temperature. The isochoric heat capacity CVand isobaric heat capacity CPof MgCaSi and Ca_(2)Si rise nonlinearly with temperature, and both CVare close to the Dulong–Petit limit at high temperature due to the negligibly small electronic contribution. The Debye temperature of both phases decrease with increasing temperature, and the downtrend for Mg Ca Si is slightly faster.However, MgCaSi possess slightly higher Debye temperature, implying the stronger chemical bonds and higher thermal conductivity than the mother phase Ca_(2)Si. The Grüneisen parameter of MgCaSi and Ca_(2)Si increase slightly with temperature, the values of MgCaSi are slightly larger. The investigation of electronic structures shows that with substitution of partial Ca by Mg in Ca_(2)Si, the stronger MgASi,MgACa and SiASi covalent bonds are formed, and plays a very significant role for the structural stability and mechanical properties.展开更多
The question here is whether the Debye model is suited to evaluate the specific heat of nanocrystals. For this, the simplest possible nanocrystal is considered: a basic cubic structure made of atoms that interact thro...The question here is whether the Debye model is suited to evaluate the specific heat of nanocrystals. For this, the simplest possible nanocrystal is considered: a basic cubic structure made of atoms that interact through a harmonic potential. This simple model can be solved exactly. This allows the dispersion relation of the mechanical waves to be determined, so that calculating the exact specific heat turns out to be quite straightforward. Then, the same problem is solved using the Debye approximation. Our findings show that the specific heat of a nanocrystal evaluated exactly is higher than the value found in the thermodynamic limit, that is to say, the specific heat decreases as the nanocrystal size increases. In addition, it becomes clear that the Debye model is a poor approximation for calculating the specific heat of a nanocrystal. Naturally, the Einstein model yields an even worse result. The cause of the discrepancy is found in the role of the nanocrystal surface.展开更多
回复电压测量方法(return voltage measurement,RVM)能有效检测变压器固体绝缘的含水量,然而对于含有局部峰值点的回复电压极化谱难以给出明确的诊断结论。文中在扩展Debye模型基础上,仿真分析了模型参数变化对极化谱和主时间常数CTC、...回复电压测量方法(return voltage measurement,RVM)能有效检测变压器固体绝缘的含水量,然而对于含有局部峰值点的回复电压极化谱难以给出明确的诊断结论。文中在扩展Debye模型基础上,仿真分析了模型参数变化对极化谱和主时间常数CTC、回复电压峰值最大值Urmax的影响规律,并提出将扩展Debye模型不同时间常数支路数作为新的特征量,最后验证了该特征量的可行性。仿真和试验结果表明:RVM极化谱前、中、尾3部分分别对应着油纸绝缘变压器油中偶极子转向极化、油纸界面极化和绝缘纸内偶极子转向极化、纸内界面极化;油纸绝缘老化会使扩展Debye模型各支路极化电阻减小,极化电容增大,时间常数减小;当变压器油老化严重时,极化谱有可能出现局部峰值;扩展Debye模型各时间常数支路数可作为新的RVM特征量,各时间常数支路数的变化也可使极化谱产生局部峰值,现场试验也验证了新特征量的有效性。展开更多
Debye-screening effects on the electron-impact excitation(EIE)processes for the dipole-allowed transition 1 s_(2)^(1)S→1 s2 p^(1)P in He-like Al^(11+)and Fe^(24+)ions are investigated using the fully relativistic dis...Debye-screening effects on the electron-impact excitation(EIE)processes for the dipole-allowed transition 1 s_(2)^(1)S→1 s2 p^(1)P in He-like Al^(11+)and Fe^(24+)ions are investigated using the fully relativistic distorted-wave methods with the Debye-Huckel(DH)model potential.Debye-screening effects on the continuum-bound(CB)interaction and target ion are discussed,both of which result in reduction of EIE cross sections.This reduction due to screening on the CB interaction is dominant.The non-spherical and spherical DH potentials are adopted for considering the screening effect on the CB interaction.It is found that the spherical DH potential could significantly overestimate the influence of plasma screening on EIE cross sections for multielectron He-like ions.展开更多
文摘The influence of pressure and temperature on the thermodynamic properties of MgCu intermetallic compound was investigated by quasi-harmonic Debye model approximation.The equation of state(EoS)parameters has performed using plane-wave pseudopotential(PW-PP)approach in the framework of the density functional theory(DFT)and the generalized gradient approximation(GGA)for the exchange-correlation functional.Our results agree well with other data of the literature.The finite temperature thermophysical properties under pressure up to 16 GPa and high temperature up to 800 K,respectively were determined.Our results of the thermophysical properties are also agree very well with other data of the literature,where for example at ambient temperature,the deviation between our obtained value(11.05 Cal mol^(−1)K^(−1))of C V,and the theoretical value(11.21 Cal mol^(−1)K^(−1))reported in the literature is only around 1.44%.The finite temperature thermophysical properties were found varied monotonically with either temperature or pressure.Compared with other materials previously studied,similar behaviors were observed.
文摘In this paper, the lattice parameter and bulk modulus of lithium(Li) at different pressures and temperatures are calculated by using the density functional theory method within the generalized gradient approximation(GGA).Through the quasi-harmonic Debye model, the thermodynamic properties of Li are predicted. The dependences of the normalized primitive cell volume V/V0 on pressure P, the variation of the thermal expansion coefficient α with pressure P and temperature T, as well as the dependences of the heat capacity Cv on pressure P and temperature T are obtained systematically in the ranges of 0~100 GPa and 0~2 000 K.
文摘Statistical expression of vapour pressure equations of metals is derived from the Debye model.The statistical distribution of T_(-p) ensemble is presented in an in-elab- orate mode and the partition function is defined.The vapour pressure of eleven metals have been calculated with the Debye equation and compared with those given by the E- instein equation and empirical equation.Comparison of results of calculation from dif- ferent methods show their evident accordance within the same orders of magnitude.
基金support from Significant Project of Guangxi Scientific Foundation (2018GXNSFDA281010)National Natural Science Foundation of China (51461002)。
文摘The thermodynamic properties of Mg Ca Si and its mother phase Ca2 Si are comparatively investigated from ab initio calculations and quasi-harmonic Debye-Grüneisen model. At 0 K, Mg Ca Si is more thermodynamically stable. Under high temperature, the advantage of higher thermodynamically stability of Mg Ca Si is reduced, originating from the less negative entropy contribution because the thermodynamic entropy of Mg Ca Si increases more slowly with temperature and the entropy values are slightly smaller.With increasing temperature, the anti-softening ability for Mg Ca Si is slightly smaller due to the slightly faster decrease trend of bulk modulus than that of Ca2 Si, although the bulk modulus of Mg Ca Si is higher in the whole temperature range considered. The thermal expansion behaviors of both Mg Ca Si and Ca_(2)Si exhibit similar increase trend, although thermal expansion coefficient of MgCaSi is slightly lower and the increases is slightly slower at lower temperature. The isochoric heat capacity CVand isobaric heat capacity CPof MgCaSi and Ca_(2)Si rise nonlinearly with temperature, and both CVare close to the Dulong–Petit limit at high temperature due to the negligibly small electronic contribution. The Debye temperature of both phases decrease with increasing temperature, and the downtrend for Mg Ca Si is slightly faster.However, MgCaSi possess slightly higher Debye temperature, implying the stronger chemical bonds and higher thermal conductivity than the mother phase Ca_(2)Si. The Grüneisen parameter of MgCaSi and Ca_(2)Si increase slightly with temperature, the values of MgCaSi are slightly larger. The investigation of electronic structures shows that with substitution of partial Ca by Mg in Ca_(2)Si, the stronger MgASi,MgACa and SiASi covalent bonds are formed, and plays a very significant role for the structural stability and mechanical properties.
文摘The question here is whether the Debye model is suited to evaluate the specific heat of nanocrystals. For this, the simplest possible nanocrystal is considered: a basic cubic structure made of atoms that interact through a harmonic potential. This simple model can be solved exactly. This allows the dispersion relation of the mechanical waves to be determined, so that calculating the exact specific heat turns out to be quite straightforward. Then, the same problem is solved using the Debye approximation. Our findings show that the specific heat of a nanocrystal evaluated exactly is higher than the value found in the thermodynamic limit, that is to say, the specific heat decreases as the nanocrystal size increases. In addition, it becomes clear that the Debye model is a poor approximation for calculating the specific heat of a nanocrystal. Naturally, the Einstein model yields an even worse result. The cause of the discrepancy is found in the role of the nanocrystal surface.
文摘回复电压测量方法(return voltage measurement,RVM)能有效检测变压器固体绝缘的含水量,然而对于含有局部峰值点的回复电压极化谱难以给出明确的诊断结论。文中在扩展Debye模型基础上,仿真分析了模型参数变化对极化谱和主时间常数CTC、回复电压峰值最大值Urmax的影响规律,并提出将扩展Debye模型不同时间常数支路数作为新的特征量,最后验证了该特征量的可行性。仿真和试验结果表明:RVM极化谱前、中、尾3部分分别对应着油纸绝缘变压器油中偶极子转向极化、油纸界面极化和绝缘纸内偶极子转向极化、纸内界面极化;油纸绝缘老化会使扩展Debye模型各支路极化电阻减小,极化电容增大,时间常数减小;当变压器油老化严重时,极化谱有可能出现局部峰值;扩展Debye模型各时间常数支路数可作为新的RVM特征量,各时间常数支路数的变化也可使极化谱产生局部峰值,现场试验也验证了新特征量的有效性。
基金Project supported by the Science Challenge Project(Grant No.TZ2016001)the National Key Research and Development Program of China(Grants Nos.2017YFA0403200 and 2017YFA0402300)+1 种基金the Funds for Innovative Fundamental Research Group Project of Gansu Province,China(Grant No.20JR5RA541)the National Natural Science Foundation of China(Grants Nos.11774037 and 12064041)。
文摘Debye-screening effects on the electron-impact excitation(EIE)processes for the dipole-allowed transition 1 s_(2)^(1)S→1 s2 p^(1)P in He-like Al^(11+)and Fe^(24+)ions are investigated using the fully relativistic distorted-wave methods with the Debye-Huckel(DH)model potential.Debye-screening effects on the continuum-bound(CB)interaction and target ion are discussed,both of which result in reduction of EIE cross sections.This reduction due to screening on the CB interaction is dominant.The non-spherical and spherical DH potentials are adopted for considering the screening effect on the CB interaction.It is found that the spherical DH potential could significantly overestimate the influence of plasma screening on EIE cross sections for multielectron He-like ions.
