Intermolecular Correlations and Mean Square Relative Displacements in C60 Fullerite

TL;DR

This study investigates intermolecular correlations and molecular displacements in high-temperature C60 fullerite using the Girifalco potential and self-consistent field methods, revealing significant anharmonic effects near the spinodal point.

Contribution

It introduces a detailed analysis of correlations and displacements in C60 fullerite at high temperatures, accounting for anharmonicity and lattice interactions.

Findings

Anharmonicity causes a sharp increase in correlations near the spinodal temperature.

Correlations vary with distance and crystallographic direction.

Comparison with solid Ar highlights interaction potential effects.

Abstract

We study molecular properties of the high-temperature modification of fullerites. In the present work we calculate the intermolecular correlations and the mean square relative displacements in C60. The Girifalco intermolecular potential is utilized. The calculations have been made in the whole interval from the equilibrium point with orientationally ordered phase up to the spinodal temperature. To take into account the lattice anharmonicity we use the correlative method of unsymmetrized self-consistent field. Its second order allows one to investigate correlations in FCC lattice between the nearest, second, third and fourth neighbors. The anharmonicity has strong effect on the intermolecular correlations at T>700 K, causing their drastic rise near the spinodal point. The dependence of the correlation moments on the distance between molecules and on the crystallographic direction is considered. We compare our results with those for solid Ar and discuss the influence of a special feature of the interaction potentials on the intermolecular correlations and the mean square molecular displacements.