Acta Crystallographica Section B

Structural Science

Volume 58, Part 4 (August 2002)

research papers

Acta Cryst. (2002). B58, 677-683 [ doi:10.1107/S0108768102004147 ]

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

J. van de Streek, P. Verwer, P. Bennema and E. Vlieg

Abstract: Discrepancies between the crystal structures of short n-alkanes 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 fields cannot reproduce the experimental observations without explicit introduction of temperature by means of molecular dynamics.

Keywords: molecular dynamics; molecular modelling; molecular mechanics; force field; polymorphism; phase transition; long-chain alkanes.


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