Theory for structure and bulk-modulus determination

TL;DR

This paper introduces a novel method for directly calculating the crystal structure, bulk modulus, and its pressure derivative of complex materials by fitting total energy data to determine equilibrium and elastic properties.

Contribution

The paper presents an explicit, exact approach enabling simultaneous determination of structure and elastic properties, including internal parameters, using polynomial fitting of total energy.

Findings

Calculated B_0 and B'_0 for selected materials using first-principles DFT.

Method accommodates complex structures with internal parameters.

Demonstrated accuracy and versatility of the approach.

Abstract

A new method for direct evaluation of both crystalline structure, bulk modulus B_0, and bulk-modulus pressure derivative B'_0 of solid materials with complex crystal structures is presented. The explicit and exact results presented here permit a multidimensional polynomial fit of the total energy as a function of all relevant structure parameters to simultaneously determine the equilibrium configuration and the elastic properties. The method allows for inclusion of general (internal) structure parameters, e.g., bond lengths and angles within the unit cell, on an equal footing with the unit-cell lattice parameters. The method is illustrated by the calculation of B_0 and B'_0 for a few selected materials with multiple structure parameters for which data is obtained by using first-principles density functional theory.