Insights into the high-pressure behaviour of solid bromine from hybrid DFT calculations

TL;DR

This study uses hybrid DFT calculations to accurately model high-pressure phases of solid bromine, predicting phase transitions and electronic properties that align well with experimental data and offering new insights into its structural behavior.

Contribution

The paper demonstrates the effectiveness of hybrid DFT in predicting high-pressure phases and transitions of bromine, including unobserved phases, improving upon GGA methods.

Findings

Predicted phase III transition at 128 GPa

Identified metallic and quasi-2D nature of phases

Incommensurate phases are transient intermediates

Abstract

Understanding the properties of molecular solids at high pressure is a key element in the development of new solid-state theories. However, the most commonly used generalized-gradient approximation (GGA) of the density functional theory (DFT) often fails to correctly describe the behavior of these systems at high pressure. Here we utilize the hybrid DFT approach to model the properties of elemental bromine at high pressure. The calculations reproduce in very good agreement with experiment the properties of the molecular phase I (Cmca symmetry) and its pressure-induced transition into the non-molecular phase II (Immm). The experimentally yet unobserved transition into phase III (I4/mmm) is predicted to occur at 128 GPa, followed by subsequent formation of an fcc lattice at 188 GPa. Analysis of the structure and electronic properties of the modelled phases indicates that the molecular Cmca phase becomes metallic just at the borderline of its stability, and that both Immm and I4/mmm phases are metallic and quasi-2D. Finally, we show that the incommensurate phases of bromine postulated from experiment are transient species which can be viewed as intermediates in the dissociation process occurring at the boundary of the transition from phase I to phase II.