Comment on “First-principles study of the influence of (110)-oriented strain on the ferroelectric properties of rutile TiO2”
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 13, 136101-1-136101-5 p.Article in journal (Refereed) Published
In a recent Brief Report, Grünebohm et al. [ Phys. Rev. B 84 132105 (2011)] report that they fail to reproduce the A2u ferroelectric instability of TiO2 in the rutile structure calculated with density functional theory within the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) by Montanari et al. [ Chem. Phys. Lett. 364 528 (2002)]. We demonstrate that this disagreement arises from an erroneous treatment of Ti 3s and 3p semicore electrons as core in their calculations. Fortuitously the effect of the frozen-semicore pseudopotential cancels the phonon instability of the PBE exchange correlation, and the combination yields phonon frequencies similar to the local density approximation harmonic values. Grünebohm et al. also attempted and failed to reproduce the soft acoustic phonon mode instability under (110) strain reported by Mitev et al. [ Phys. Rev. B 81 134303 (2010)]. For this mode the combination of PBE-GGA and frozen semicore yields a small imaginary frequency of 9.8i. The failure of Grünebohm et al. to find this mode probably arose from numerical limitations of the geometry optimization approach in the presence of a shallow double well potential; the optimization method is not suitable for locating such instabilities.
Place, publisher, year, edition, pages
New York: American Physical Society , 2013. Vol. 88, no 13, 136101-1-136101-5 p.
IdentifiersURN: urn:nbn:se:uu:diva-211869DOI: 10.1103/PhysRevB.88.136101OAI: oai:DiVA.org:uu-211869DiVA: diva2:669054