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

TL;DR

This paper presents the implementation of orbital-free free-energy functionals in the Profess code, coupling it with Quantum Espresso to enable high-temperature ab initio molecular dynamics simulations that are significantly faster than traditional Kohn-Sham methods.

Contribution

The paper introduces a coupled orbital-free DFT framework with Quantum Espresso, allowing efficient high-temperature molecular dynamics simulations without the orbital bottleneck.

Findings

Orbital-free DFT simulations are 3 to 100 times faster than Kohn-Sham DFT.

Enables high-temperature MD simulations on ordinary computers.

Successfully simulated hydrogen from 2,000 K to 4,000,000 K.

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.