VIRIAL-COEFFICIENTS AND EQUATION OF STATE OF HARD ALKANE MODELS

The virial coefficients up to the fifth of hard conformers of alkanes have been evaluated numerically. The conformers were selected by using the rotational isomeric state approximation. The effect of branching and length of the chain on the anisotropy of alkanes is discussed and a relation between the nonsphericity parameter alpha and the acentric factor omega for this kind of molecule is proposed. We modified the equation of state for tangent hard spheres first proposed by Wertheim [M. S. Wertheim, J. Chem. Phys. 87, 7323, (1987)] to allow for overlapping of the constituting hard spheres. This modified version predicts with high accuracy the virial coefficient of the hard conformers of alkanes. Moreover comparison of this equation of state with simulation results of repulsive models of n-alkanes reveals very good agreement. The effect of condensed phase effect on the conformational equilibria of n-alkanes up to n-octane is analyzed.