Abstract
Thermodynamic properties of real gases can be accurately described using realistic intermolecular potential energy surfaces. In this work, a first-order correction to the ideal gas equation of state is introduced through the computation of the classical second virial coefficient, B(T), derived from the configurational partition function, which explicitly depends on the intermolecular interaction potential. As a case study, the double many-body expansion (DMBE) potential energy surface for the ground electronic state of the N(2)H(2) system was employed to derive pairwise interaction potentials for H(2)···N(2) and NH···NH. These potentials were used to numerically evaluate the canonical partition function. Second virial coefficients, compressibility factors, and constant-volume heat capacities were computed in the temperature range 30-2000 K. The calculated B(T) values for H(2)···N(2) are in good agreement with previous literature data, while the results for NH···NH lie within expected trends observed for similar systems.