Ideal Gas Helmholtz Energy Model Implementation Based on Quantum Chemical Data and Application to Equation of State Modeling

Ideal gas thermodynamic properties are essential for
many industrial
processes. In this work, an implementation of an ideal gas Helmholtz
energy contribution model based on statistical mechanics and quantum
chemistry ab initio data is given. The energy storage properties of
individual molecules are described in the model by the classical rigid-rotor
and harmonic oscillatorfor the independent normal modes. Quantum
mechanical calculations using density functional theory were performed
for about 21,500 molecules to determine the vibrational and rotational
energy levels. The model predictions were validated using experimental
isobaric heat capacity data from the literature for approximately
1,000 molecules. The model yields average deviations of 0.5–8%,
with over 91% of the molecules showing deviations below 5%. We demonstrate
the applicability of the ideal gas model in combination with a molecular-based
equation of state, the SAFT-VR Mie (J. Chem. Phys. 2013 139, 154504), to describe different
thermodynamic properties.