title: Determination of the structural parameters of an incommensurate phase from first principles: the case of Sc-II.
abstract: We propose a procedure to accurately describe the structural parameters of an incommensurate phase using ab initio methods by approximating it with a set of analogous commensurate supercells. We apply this approach to obtain the structural parameters of the Sc-II phase, which has recently been identified as a complex incommensurate structure similar to Sr-V. The calculated incommensurate ratio gamma, lattice parameters, and Wyckoff positions of Sc-II are in excellent agreement with the available experimental data. Our results show that gamma increases with pressure up to 60 GPa approaching but never reaching the commensurate value 4/3. Hence calculations do not confirm the prediction made based on the reanalyzing of experimental data. When pressure exceeds 70 GPa, gamma shows a sharp decrease that might be considered as the precursor of a new structural phase transition.
authors.affiliation: Division of Materials Theory, Department of Physics and Materials Science, Uppsala University, Box 530, S-751 21 Uppsala, Sweden. Sergui.Arapan@fysik.uu.se
authors.forename: Sergiu
authors.initials: S
authors.lastname: Arapan
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Skorodumova
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ahuja