Origin of complex crystal structures of elements at pressure

TL;DR

This paper introduces a unifying theory based on the nearly free electron model to explain the complex crystal structures of sp-bonded elements under pressure, linking Fermi-surface interactions to structural stability and properties.

Contribution

It provides a simple, unified explanation for complex high-pressure structures of elements using FSBZ interactions within the nearly free electron framework.

Findings

Explains observed crystal structures under pressure

Describes evolution of structural parameters with pressure

Validates theory with experimental and ab initio data

Abstract

We present a unifying theory for the observed complex structures of the sp-bonded elements under pressure based on nearly free electron picture (NFE). In the intermediate pressure regime the dominant contribution to crystal structure arises from Fermi-surface Brillouin zone (FSBZ) interactions - structures which allow this are favoured. This simple theory explains the observed crystal structures, transport properties, the evolution of internal and unit cell parameters with pressure. We illustrate it with experimental data for these elements and ab initio calculation for Li.