The Pseudopotential Approach within Density-Functional Theory: The Case of Atomic Metallic Hydrogen

Jin Zhang,Jeevake Attapattu,Jeffrey M Mcmahon

doi:10.3390/condmat5040074

Jin Zhang, Jeevake Attapattu + Show 1 more

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https://doi.org/10.3390/condmat5040074

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Journal: Condensed Matter	Publication Date: Nov 13, 2020
Citations: 1	License type: CC BY 4.0

Affiliation: Washington State University

Abstract

Internal energies, enthalpies, phonon dispersion curves, and superconductivity of atomic metallic hydrogen are calculated. The standard use of pseudopotentials in density-functional theory are compared with full Coulomb-potential, all-electron linear muffin-tin orbital calculations. Quantitatively similar results are found as far as internal energies are concerned. Larger differences are found for phase-transition pressures; significant enough to affect the phase diagram. Electron–phonon spectral functions α2F(ω) also show significant differences. Against expectation, the estimated superconducting critical-temperature Tc of the first atomic metallic phase I41/amd (Cs-IV) at 500 GPa is actually higher.

Highlights

Hydrogen is the simplest and most abundant element in the universe
Volumes were determined by geometry optimizations with QUANTUM ESPRESSO (QE) over the considered pressure range in steps of 500 GPa
The reliability of the standard use of pseudopotentials to simulate atomic metallic hydrogen was studied. This was done for calculations of internal energy, enthalpy, the phonon dispersion spectrum, and superconductivity, by comparing pseudopotential to all-electron calculations

Summary

Introduction

Hydrogen is the simplest and most abundant element in the universe. First it solidifies and crystallizes, and it evolves through a series of high-density solid phases. In 1935, Wigner and Huntington predicted [1] that sufficient pressure would even dissociate hydrogen molecules, and that any Bravais lattice of such atoms would be metallic. The problem of metallic hydrogen has received considerable attention, as reviewed in Ref. The structures and stabilities of atomic metallic hydrogen are considered. The background of what is known (from calculations; as motivated below) and relevant to this work will be discussed in context

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