Helium under high pressure: A comparative study of all-electron and pseudopotential methods within density functional theory

TL;DR

This study compares all-electron and pseudopotential methods within DFT to analyze helium's electronic structure under high pressure, confirming pseudopotentials' accuracy across a wide pressure range and identifying the most stable crystal structure.

Contribution

It demonstrates that pseudopotential methods reliably reproduce all-electron results for helium under high pressure, validating their use in extreme conditions simulations.

Findings

Pseudopotentials match all-electron methods for energy-volume curves.

hcp is the most stable helium structure under high pressure.

Phase transition predictions require more precise electron correlation methods.

Abstract

We have calculated the ground state electronic structure of He under pressure from 0 to 1500 GPa using both all-electron full-potential and pseudopotential methods based on the density functional theory (DFT). We find that throughout this pressure range, pseudopotentials yield essentially the same energy-volume curve for all of bcc, fcc, and hcp configurations as does the full-potential method, a strong indication that pseudopotential approximation works well for He both as the common element in some giant planets and as detrimental impurities in fusion reactor materials. The hcp lattice is always the most stable structure and bcc the least stable one. Since the energy preference of hcp over fcc and bcc is within 0.01 eV below 100 GPa and about 0.1 eV at 1500 GPa, on the same order of the error bar in local or semi-local density approximations in DFT, phase transitions can only be discussed with more precise description of electron correlation in Quantum Monte Carlo or DFT-based GW methods.