Orbital-free Molecular Dynamics Simulations to Characterize the Liquid-vapor Critical Point of Aluminum

Aluminum is frequently used in warm-dense matter (WDM) experiments. However, experimental diagnostic limitations make computational exploration of the Al liquid-vapor transition important[1]. The elevated temperaure and low-density make ab initio molecular dynamics (AIMD) with Kohn-Sham (KS) density functional theory (DFT) searches for the divergent compressibility extremely time consuming. Orbital free DFT (OFDFT) in principle is a cost-effective alternative. Here we report on calculations utilizing the PROFESS@QuantumEspresso interface [2] to explore suitable pseudo-potentials [3], the limitations of our wholly constraint-based VT84F [4] non-ineracting free-energy functional as exposed in the low-density regime, and possible extensions or extrapolations via tunable non-interacting free energy functionals [5]. [1] Atom.\ Proc.\ Plasmas \textbf{CP-1161} K.\ B.\ Fournier\ ed.\ (2009); [2] Comput.\ Phys.\ Commun.\ \textbf{185}, 3240 (2014); [3] J.\ Phys.:\ Condens.\ Matter \textbf{2}, 351 (1990); [4] Phys.\ Rev.\ B \textbf{88}, 161108(R) (2013); [5] ``Tunable non-interacting free-energy functionals", V.V.\ Karasiev \{unpublished\}