Determination of Energy Parameters in Lennard-Jones Potentials from Second Virial Coefficients

Abstract

The energy parameters in Lennard-Jones 6-12 potential between atoms (hydrogen, oxygen, nitrogen and carbon) were estimated from second virial coefficients of diatomic gases (H2, O2, N2, NO and CO) and methane (CH4), assuming the additivity of atomic potentials and the combination rules for unlike pairs. The results show that there is a certain relation between the two parameters (van der Waals radius, rw and the parameter of the attractive part, e) when the calculated virial coefficients are in agreement with the experimental data over a wide range of temperature. According to the relation one can select reasonable sets of parameters for atoms, which reproduce the experimental virial coefficients. In general, the best fit values of rw for H, N and C atom were somewhat greater than those usually adopted. As for H-H interaction the parameters obtained from the virial data of H2 differ from those from CH4 due presumably to deviation of simple additivity of atomic interactions. The relation between rw and e is available for justification or estimation of the energy parameters in atomic potentials, since any given atomic potential may have parameters which satisfy the relation or we can determine one of the parameters by the use of the relation if the other is found from the other measurements.