Finite-temperature orbital-free DFT molecular dynamics: Coupling Profess and Quantum Espresso
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 KohnSham (KS) DFT. All the non-interacting free-energy functionals implemented are single-point: the local density approximation (LDA; also known as finite-T ThomasFermi, 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 2000 K ? T ? 4,000,000 K are reported, with timings on small clusters (16128 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.
finite-temperature orbital-free density functional theory electronic structure ab-initio molecular dynamics non-interacting free energy exchangecorrelation free energy