First-principles thermal equation of state and thermoelasticity for hcp Fe under high pressures

Abstract

We investigate the equation of state and elastic properties of nonmagnetic hcp iron at high pressures and high temperatures using the first principles linear response linear-muffin-tin-orbital method in the generalized-gradient approximation. We calculate the Helmholtz free energy as a function of volume, temperature, and volume-constrained strain, including the electronic excitation contributions from band structures and lattice vibrational contributions from quasi-harmonic lattice dynamics. We perform detailed investigations on the behavior of elastic moduli and equation of state properties as a function of temperature and pressure, including the pressure-volume equation of state, bulk modulus, the thermal expansion coefficient, the Gruneisen ratio, and the shock Hugoniots. A detailed comparison has been made with available experimental measurements and theoretical predictions.