On the influence of thermal motion on the crystal structures and polymorphism of even n-alkanes

Abstract

# 2002 International Union of Crystallography Printed in Great Britain ± all rights reserved Discrepancies between the crystal structures of short nalkanes as obtained from experiment and as obtained from molecular mechanics tended to worsen at longer chain lengths. The same holds for the relative stabilities of the two experimentally observed polymorphs. In this paper it is argued that the discrepancies are caused by thermal effects, and that the triclinic polymorph is the most stable polymorph for all chain lengths at 0 K. A phase transition is predicted but has yet to be found experimentally. Current force ®elds cannot reproduce the experimental observations without explicit introduction of temperature by means of molecular dynamics. Received 27 November 2001 Accepted 4 March 2002