Ab initiothermodynamics beyond the quasiharmonic approximation: W as a prototype

Abstract

We present a simple but accurate scheme to compute the thermodynamic properties of crystalline solids in a wide range of pressure and temperature based on ab initio calculations. Compared to the method based on ab initio thermodynamic-integration techniques, our approach can reduce dramatically the number of ab initio molecular-dynamics simulations needed in the calculations of the intrinsic anharmonic effect neglected in the conventional quasiharmonic approximation. Taking tungsten as an example, we show that its thermal properties including the linear thermal-expansion coefficient and the equation of state ͑EOS͒ at high pressures and temperatures can be calculated accurately. The precise EOS of W for the pressure up to 500 GPa and the temperature up to 10 000 K may serve as a pressure scale. This method may be able to be extended to the study of solid-solid phase transitions of various crystalline solids, including some alloys.

Single-crystal X-ray diffraction at megabar pressures and temperatures of thousands of degrees

“…Figure 3 shows that the present results are in good agreement with ab initio predictions [22], raising confidence in both experimental and theoretical methodologies. (1)- (3) [15].…”

“…The pressures of the red data points and for the curves were determined using the fitted thermal EOS parameters. The inset shows the difference between the values of the measured unit cell volumes and the values obtained from the thermal equations of state in the present study (blue plus symbols) and the values predicted based on ab initio calculations (pink crosses) [22] (color online).…”

“…Tungsten naturally satisfies these conditions and its accurate equation of state at ambient temperature has already been measured, based on single-crystal compression experiments up to above 150 GPa [21]. There are theoretical predictions on the thermal equation of state (EOS) of tungsten (see [22] and references therein), but experimental static compression data at high temperatures are lacking. We determined the lattice parameters of tungsten single crystals compressed in an Ne pressure-transmitting medium (which can also be used as an internal pressure standard [23]; Figure 2).…”

First-principles simulation on thermoelectric properties in Bi-Sb System

“…The first-principles phonon frequencies were calculated by diagonalization of the dynamical matrix with numerical force constants from the 2 ´ 2 ´ 2 supercell. The results due to the QHA have been known as to be in good agreement with experimental behaviors for thermal expansion and contraction [23][24][25][26][27][28].…”

High-energy asymptotic behavior of the S matrix in the saturation region with the smallest dipole running coupling prescription

“…However, this numerical process is very cumbersome to use in practice, due to the intricate programming for solving an integro-differential equation and time-costing for running the program. In order to facilitate the use of the BK equation in direct phenomenological application, a lot of efforts were devoted to establish an analytical dipole scattering amplitude in the literature [25][26][27][28][29][30]. Among them, we analytically solved the full NLO BK equation in the saturation region [29].…”