Equation of state of paramagnetic CrN from ab initio molecular dynamics

TL;DR

This paper introduces a first-principles molecular dynamics method to calculate the equation of state of paramagnetic CrN, addressing challenges in simulating magnetic disorder and providing insights into its bulk modulus.

Contribution

A novel ab initio molecular dynamics approach for magnetic materials in their high-temperature paramagnetic phase is proposed and applied to CrN.

Findings

Bulk modulus in paramagnetic CrN is similar to antiferromagnetic phase.

The method effectively simulates magnetic disorder at finite temperatures.

Results clarify the debated equation of state of CrN.

Abstract

Equation of state for chromium nitride has been debated in the literature in connection with a proposed collapse of its bulk modulus following the pressure induced transition from the paramagnetic cubic phase to the antiferromagnetic orthorhombic phase [F. Rivadulla et al., Nat Mater 8, 974 (2009); B. Alling et al., Nat Mater 9, 283 (2010)]. Experimentally the measurements are complicated due to the low transition pressure, while theoretically the simulation of magnetic disorder represent a major challenge. Here a first-principles method is suggested for the calculation of thermodynamic properties of magnetic materials in their high temperature paramagnetic phase. It is based on ab-initio molecular dynamics and simultaneous redistributions of the disordered but finite local magnetic moments. We apply this disordered local moments molecular dynamics method to the case of CrN and simulate its equation of state. In particular the debated bulk modulus is calculated in the paramagnetic cubic phase and is shown to be very similar to that of the antiferromagnetic orthorhombic CrN phase for all considered temperatures.