Combined quantum-mechanical and Calphad approach to description of heat capacity of pure elements below room temperature

摘要

Einstein temperature (T-E) was determined by fitting of experimental heat capacity data by the Einstein function only which ensures that it will represent the harmonic vibrational Gibbs energy only. The values of the electronic and anharmonic contributions to Gibbs energy (heat capacity) of 51 elements in stable state are determined by fitting the parameters of polynomials describing these contributions to SGTE data at T-lim. Polynomials published by Chen and Sundman (2001) were used. Parameters a, b, and c of those polynomials have a particular physical meaning in the temperature interval (0 < T < T-lim) (in K) only (T-lim is the low-temperature limit of validity of SGTE data). For illustration, the results of calculation of heat capacities in low-temperature region performed by PHON software are presented. Gained thermodynamic data make it possible to perform correct Calphad modeling of phase diagrams below room temperature; for this purpose, the SGTE-type formulas (in the form of G-HSER) for Gibbs energies of 51 elements studied are provided. The aim of this paper is to show relative simple and physically correct way to extend the SGTE data to 0 K, which can be supported by ab initio phonon calculations in the future. (C) 2015 Elsevier Ltd. All rights reserved.