arXiv subjects

Xing-Yu Gao

Publications and source records attributed to Xing-Yu Gao.

4 recordsLinked to original sources

arXiv2024

Self-consistent pressure-dependent on-site Coulomb correction for zero-temperature equations of state of $f$-electron metals

The $f$-electron materials have many unique properties under pressure, thus of great interest in high-pressure physics and related industrial fields. However, the $f$-electrons pose a substantial challenge to simulations since the electron correlation effects. In this work, we present a first-principles calculation scheme for the equations of state (EoS) of $f$-electron materials. The self-consistent pressure-dependent on-site Coulomb correction is performed based on our recently developed doubly screened Coulomb correction approach. We investigate the zero-temperature EoS over a wide range of pressures and the phase stabilities of four prototypical lanthanide and actinide metals, Pr, Eu, Th and U. The simulated compressive properties are in better agreement with the experimental data than those obtained by conventional density functional theory (DFT) and fixed-parameter DFT+$U$ approaches. The pressure-induced phase transitions can also be well described.

cond-mat.str-el↗

arXiv2022

The underestimation of high pressure in DFT+$U$ simulation for the wide range cold-pressure of lanthanide metals

Density functional theory plus $U$ (DFT+$U$) is one of the most efficient first-principles methods to simulate the cold pressure properties of strongly-correlated materials. However, the applicability of DFT+$U$ at ultra-high pressure is not sufficiently studied, especially in the widely-used augmented schemes [such as projector augmented wave (PAW) and linearized augmented plane wave (LAPW)]. This work has systematically investigated the performance of DFT+$U$ in PAW and LAPW at the pressure up to several hundred GPa for the lanthanide metals, which is a typical strongly-correlated series. We found DFT+$U$ simulation in PAW exhibits an unphysical underestimating of force at high pressure. By delicate analysis and comparison with local-orbital-independent hybrid functional results, we have demonstrated that this unphysical behavior is related to a normalization problem on the local density matrix caused by the overlap of local orbitals in PAW under high pressure. Additionally, we observed a slight softening of force in DFT+$U$ in heavy lanthanides (Tm, Yb and Lu) at high pressure comparing with the DFT results without the influence of local orbital overlap, and it might be related to the enhancement of bonding effect in correlation correction methods at high pressure. Our work reveals the underestimating of high pressure in DFT+$U$ simulation, analyses two sources of this unusual behavior and proposes their mechanism. Most importantly, our investigation highlights the breakdown of DFT+$U$ for high pressure simulation in VASP package based on PAW framework.

cond-mat.mtrl-sci↗

arXiv2019

A first principles study of high pressure phase diagram of bismuth at 0 ~14 GPa based on structure search and quasi-harmonic approximation

We have performed first principles study for bismuth crystal structure at pressure from 0~14 GPa based on structure search and quasi-harmonic approximation. A new stable phase with Pbcm symmetry is predicted by structure search method. We find that the most stable structures of bismuth at 0 K are R-3m(0 ~ 3.29 GPa), Pbcm (3.29 GPa ~ 4.91 GPa), Cmce (4.91 GPa ~ 10.57 GPa) and Im-3m ( > 10.57 GPa), respectively. By quasi-harmonic approximation, we predicted the phase diagram of bismuth from first principles calculations. We found that the phase transition pressure reduces with increasing temperature. Our calculation agrees with the trend of experimental phase diagram. The P4/ncc model structure for the incommensurate Bi-III phase is not a stable phase in our calculation. A better model for the Bi-III phase is still needed. We also note that the spin-orbital interaction is very important for phase-diagram simulation of bismuth. By using first principle based structure search method, we successfully determine the low temperature high pressure phase diagram of bismuth, showing that the structure search method can effectively find the most stable structure of given material at high pressure even with high Z elements.

cond-mat.mtrl-sci↗

arXiv2017

New zirconium hydrides predicted by structure search method based on first principles calculations

The formation of precipitated zirconium (Zr) hydrides is closely related to the hydrogen embrittlement problem for the cladding materials of pressured water reactors (PWR). In this work, we systematically investigated the crystal structures of zirconium hydride (ZrHx) with different hydrogen concentrations (x = 0~2, atomic ratio) by combining the basin hopping algorithm with first principles calculations. We conclude that the P3m1 ζ-ZrH0.5 is dynamically unstable, while a novel dynamically stable P3m1 ZrH0.5 structure was discovered in the structure search. The stability of bistable P42/nnm ZrH1.5 structures and I4/mmm ZrH2 structures are also revisited. We find that the P42/nnm (c/a > 1) ZrH1.5 is dynamically unstable, while the I4/mmm (c/a = 1.57) ZrH2 is dynamically stable.The P42/nnm (c/a < 1) ZrH1.5 might be a key intermediate phase for the transition of γ->δ->ε phases. Additionally, by using the thermal dynamic simulations, we find that δ-ZrH1.5 is the most stable structure at high temperature while ZrH2 is the most stable hydride at low temperature. Slow cooling process will promote the formation of δ-ZrH1.5, and fast cooling process will promote the formation of γ-ZrH. These results may help to understand the phase transitions of zirconium hydrides.

cond-mat.mtrl-sci↗