A new method for calculating the thermodynamic and physical properties of compounds: Application to Laves phase Fe2Mo

Physica B: Condensed Matter. 2021. Vol. 621. No. 15. Article 413307.

Vasilyev Dmitry

In this work, a new method of searching a most energetically favorable free energy calculated along different thermal expansion paths of a compound is proposed. This makes it possible to reduce the problem to a one-dimensional case and to consider free energy as having one variable - volume. The method was applied to study the thermodynamics of Laves phase Fe2Mo. The thermodynamic and physical properties of Fe2Mo have been investigated using the finite-temperature quantum mechanical calculations within the frame of the density functional theory (DFT). All relevant free energy contributions including electronic, vibrational and magnetic excitations are considered. The quasi-harmonic Debye - Grüneisen theory is used. The heat capacity, thermal expansion, elastic constants and bulk modulus are modelled. The calculated results analyzed and are in an agreement with the available experimental data. It is shown that magnetic entropy must be considered on equal footing with vibrational and electronic energies to reliably predict stability of Fe2Mo.

Keywords: термодинамика, температура Дебая, Debye temperature, equilibrium thermodynamics, Thermal expansion, Stress tensor, тензор напряжений, термическое расширение, DFT ab initio calculations, DFT расчеты