Finite-temperature orbital-free DFT molecular dynamics: Coupling Profess and Quantum Espresso

Abstract

Implementation of orbital-free free-energy functionals in the Profess code and the coupling of Profess with the Quantum Espresso code are described. The combination enables orbital-free DFT to drive ab initio molecular dynamics simulations on the same footing (algorithms, thermostats, convergence parameters, etc.) as for Kohn-Sham (KS) DFT. All the non-interacting free-energy functionals implemented are single-point: the local density approximation (LDA; also known as finite-T Thomas-Fermi, ftTF), the second-order gradient approximation (SGA or finite-T gradient-corrected TF), and our recently introduced finite-T generalized gradient approximations (ftGGA). Elimination of the KS orbital bottleneck via orbital-free methodology enables high-T simulations on ordinary computers, whereas those simulations would be costly or even prohibitively time-consuming for KS molecular dynamics (MD) on very high-performance computer systems. Example MD simulations on H over a temperature range 2, 000 K ≤ T ≤ 4, 000, 000 K are reported, with timings on small clusters (16-128 cores) and even laptops. With respect to KS-driven calculations, the orbital-free calculations are between a few times through a few hundreds of times faster.

Extended application of Kohn-Sham first-principles molecular dynamics method with plane wave approximation at high energy—From cold materials to hot dense plasmas

“…26,27 Instead, the method adopts the original idea of density functional the-ory, formulating the free energy as a functional of electron charge density. 13,28 Usually, the Thomas-Fermi approximation is applied to the kinetic part. It has a much improved computational efficiency but at the expense of being less accurate at low temperature.…”

Nonempirical Semilocal Free-Energy Density Functional for Matter under Extreme Conditions

“…Because LDA is widely viewed as good for metals, PZ is used as the reference. Calculations were done with a locally modified version of Quantum-Espresso [79,80]. For the PZ and corrKSDT functionals we used a PAW data set built with PZ XC.…”

Towards accurate orbital-free simulations: A generalized gradient approximation for the noninteracting free energy density functional

“…The AIMD calculations were for the equation of state (EOS) of hydrogen (H), deuterium (D), and Al. Whether driven by conventional KS or OFDFT forces, the calculations were performed on the same footing with the profess@Quantum-Espresso package 38 and the same groundstate XC functional (PZ) as in the static cases. The bulk densities used were chosen such that the D EOS results could be compared with published PIMC values 39 .…”

“…The bulk densities used were chosen such that the D EOS results could be compared with published PIMC values 39 . For H and D, in both the KS-AIMD and OF-AIMD calculations the electron-ion interaction was treated via a deep local pseudopotential 38 with core radius 0.25 bohr. For Al, the KS-AIMD calculations used the non-local PAW dataset (Al.pzn-kjpaw psl.0.1.UPF) 40 , and the PZ XC functional, while the OF-AIMD calculations used the aforementioned BLPS.…”