Ab initio molecular dynamics simulations of negative thermal expansion in ScF3: The effect of the supercell size
Date
2020
Authors
Krack, M.
Bocharov, Dmitry
Rafalskij, Yuri
Kuzmin, Alexei
Purans, Juris
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier B.V.
Abstract
Scandium fluoride (ScF3) belongs to a class of negative thermal expansion (NTE) materials. It shows a strong lattice contraction up to about 1000 K switching to expansion at higher temperatures. Here the NTE effect in ScF3 is studied in the temperature range from 300 K to 1600 K using ab initio molecular dynamics (AIMD) simulations in the isothermal-isobaric (NpT) ensemble. The temperature dependence of the lattice constant, inter-atomic Sc–F–Sc bond angle distributions and the Sc–F and Sc–Sc radial distribution functions is obtained as a function of supercell size from 2a × 2a × 2a to 5a × 5a × 5a where a is the lattice parameter of ScF3. A comparison with the experimental Sc K-edge EXAFS data at 600 K is used to validate the accuracy of the AIMD simulations. Our results suggest that the AIMD calculations are able to reproduce qualitatively the NTE effect in ScF3, however a supercell size larger than 2a × 2a × 2a should be used to account accurately for dynamic disorder. The origin of the NTE in ScF3 is explained by the interplay between expansion and rotation of ScF6 octahedra
Description
The authors sincerely thank S. Ali, A. Kalinko, and F. Rocca for providing experimental EXAFS data, as well as M. Isupova, V. Kashcheyevs, and A. I. Popov for stimulating discussions. Financial support provided by project No. 1.1.1.2/VIAA/l/16/147 (1.1.1.2/16/I/001) under the activity “Post-doctoral research aid” realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged by D.B. A.K and J.P. would like to thank the support of the Latvian Council of Science project No. lzp-2018/2–0353.
Keywords
Ab initio molecular dynamics , CP2K , EXAFS , Negative thermal expansion , ScF3 , Research Subject Categories::NATURAL SCIENCES:Physics