Department of Physics Papers

Document Type

Journal Article

Date of this Version

8-15-1992

Publication Source

Physical Review B

Volume

46

Issue

8

Start Page

4944

Last Page

4957

DOI

10.1103/PhysRevB.46.4944

Abstract

We determine the allowed structures for orientationally ordered icosahedral molecules on a fcc lattice such that there are four molecules per simple-cubic unit cell. The allowed space groups are Pm3, Pn3, and Pa3. In the latter two, an angle of rotation assumes a value not fixed by symmetry. The locations of all 240 atoms in the unit cell as deduced from the powder x-ray data of Heiney et al. are tabulated. We discuss a number of minima in the free energy which correspond to the observed Pa3 structure of solid C60. We introduce orientational order parameters which lead to a Landau free energy, from which we predict that the orientational transition is discontinuous.

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Date Posted: 12 August 2015

This document has been peer reviewed.