Equation of state and phonon frequency calculations of diamond at high pressures

TL;DR

This study uses advanced computational methods to calculate the equation of state and phonon frequencies of diamond under extremely high pressures up to 600 GPa, comparing results with experimental data.

Contribution

It provides a comprehensive comparison of three different computational approaches for high-pressure diamond properties within DFT.

Findings

All methods yield consistent pressure derivatives of bulk modulus.

Results differ from recent experimental measurements up to 140 GPa.

Implications for pressure calibration methods are discussed.

Abstract

The pressure-volume relationship and the zone-center optical phonon frequency of cubic diamond at pressures up to 600 GPa have been calculated based on Density Functional Theory within the Local Density Approximation and the Generalized Gradient Approximation. Three different approaches, viz. a pseudopotential method applied in the basis of plane waves, an all-electron method relying on Augmented Plane Waves plus Local Orbitals, and an intermediate approach implemented in the basis of Projector Augmented Waves have been used. All these methods and approximations yield consistent results for the pressure derivative of the bulk modulus and the volume dependence of the mode Grueneisen parameter of diamond. The results are at variance with recent precise measurements up to 140 GPa. Possible implications for the experimental pressure determination based on the ruby luminescence method are discussed.