Linear response separation of a solid into atomic constituents: Li, Al, and their evolution under pressure

TL;DR

This paper introduces the enatom concept, a linear response-based method to decompose a solid's charge density into atomic contributions, revealing how atomic behavior evolves under pressure in Li and Al.

Contribution

It presents the first implementation of the enatom decomposition, providing a new way to analyze atomic contributions and their pressure-dependent evolution in solids.

Findings

Li shows increased covalency under pressure, unlike Al.

Nonrigid charge and potential parts have opposite signs in Li and Al.

Enatom potential aids understanding of vibrational and electron-phonon properties.

Abstract

We present the first realization of the generalized pseudoatom concept introduced by Ball, and adopt the name enatom to minimize confusion. This enatom, which consists of a unique decomposition of the total charge density (or potential) of any solid into a sum of overlapping atomiclike contributions that move rigidly with the nuclei to first order, is calculated using (numerical) linear response methods, and is analyzed for both fcc Li and Al at pressures of 0, 35, and 50 GPa. These two simple fcc metals (Li is fcc and a good superconductor in the 20-40 GPa range) show different physical behaviors under pressure, which reflects the increasing covalency in Li and the lack of it in Al. The nonrigid (deformation) parts of the enatom charge and potential have opposite signs in Li and Al; they become larger under pressure only in Li. These results establish a method of construction of the enatom, whose potential can be used to obtain a real-space understanding of the vibrational properties and electron-phonon interaction in solids.