CpFit program implements thermodynamic model of heat capacity and other thermodynamic functions based on usage of Einstein-Plank functions sum and empirical parameters. The used approach has been developed by Voronin et al. .
All thermodynamic functions (e.g. heat capacity, entropy and enthalpy) are represented as sums of Einstein-Plank terms:
where and are adjustable (usually by means of the least squares method) model parameters. They can be estimated from experimental data using least squares method. A universal gas constant value from CODATA 2014 is used in the CpFit program. In the eqs values are dimensionless and values are expressed in K.
The thermodynamic model of heat capacity based on Einstein-Plank functions allows to approximate , and in a wide temperature range using a uniﬁed set of parameters. Also unlike polynomial models it can give a physically correct extrapolation to a wider temperature range.
Implementation of this model in CpFit hides all analytical expressions and technical details and allow to use it as an ordinary statistical package for a nonlinear regression. Alexey L.Voskov, Ilya B.Kutsenok, Gennady F.Voronin CpFit program for approximation of heat capacities and enthalpies by Einstein-Planck functions sum // Calphad, 2018, 61, 50-61  Gennady F. Voronin, Ilya B. Kutsenok Universal Method for Approximating the Standard Thermodynamic Functions of Solids // J. Chem. Eng. Data, 2013, 58, 2083−2094