A jumping crystal predicted with molecular dynamics and analysed with TLS refinement against powder diffraction data

Jacco van de Streek; Edith Alig; Simon Parsons; Liana Vella-Zarb

doi:10.1107/S205225251801686X

A jumping crystal predicted with molecular dynamics and analysed with TLS refinement against powder diffraction data

IUCrJ. 2019 Jan 1;6(Pt 1):136-144. doi: 10.1107/S205225251801686X.

Authors

Jacco van de Streek^{1

2}, Edith Alig², Simon Parsons³, Liana Vella-Zarb⁴

Affiliations

¹ Department of Pharmacy, University of Copenhagen, Copenhagen, Denmark.
² Institute for Inorganic and Analytical Chemistry, Goethe-University Frankfurt, Frankfurt am Main, Germany.
³ School of Chemistry/Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh, UK.
⁴ Chemistry Department, University of Malta, Msida, Malta.

Abstract

By running a temperature series of molecular dynamics (MD) simulations starting from the known low-temperature phase, the experimentally observed phase transition in a 'jumping crystal' was captured, thereby providing a prediction of the unknown crystal structure of the high-temperature phase and clarifying the phase-transition mechanism. The phase transition is accompanied by a discontinuity in two of the unit-cell parameters. The structure of the high-temperature phase is very similar to that of the low-temperature phase. The anisotropic displacement parameters calculated from the MD simulations readily identified libration as the driving force behind the phase transition. Both the predicted crystal structure and the phase-transition mechanism were verified experimentally using TLS (translation, libration, screw) refinement against X-ray powder diffraction data.

Keywords: TLS refinement; XRPD; jumping crystals; molecular dynamics; phase transitions.

Grants and funding

This work was funded by Lundbeckfonden grant R49-A5604. Villum Fonden grant VKR023111.