Lattice dynamics and thermodynamics of bcc iron at pressure: first-principles linear response study

TL;DR

This study uses first-principles linear response calculations to analyze the lattice dynamics and thermodynamic properties of ferromagnetic bcc iron under pressure, showing good agreement with experimental data.

Contribution

It provides a comprehensive first-principles analysis of phonon and thermodynamic properties of bcc iron at various pressures and temperatures, including electronic and phonon contributions.

Findings

Phonon dispersion matches neutron scattering data.

Thermodynamic properties agree with diamond-anvil-cell measurements.

Behavior of bulk modulus and heat capacity characterized under pressure.

Abstract

We compute the lattice-dynamical and thermal equation of state properties of ferromagnetic bcc iron using the first principles linear response linear-muffin-tin-orbital method in the generalized-gradient approximation. The calculated phonon dispersion and phonon density of states, both at ambient and high pressures, show good agreement with inelastic neutron scattering data. We find the free energy as a function of volume and temperature, including both electronic excitations and phonon contributions, and we have derived various thermodynamic properties at high pressure and temperature. The thermal equation of state at ambient temperature agrees well with diamond-anvil-cell measurements. We have performed detailed investigations on the behavior of various thermal equation of state parameters, such as the bulk modulus, the thermal expansivity, the Anderson-Gruneisen parameter, the Gruneisen ratio, and the heat capacity as function of temperature and pressure. A detailed comparison has been made with available experimental measurements, as well as results from similar theoretical studies on nonmagnetic bcc Tantalum.