The physical significance of imaginary phonon modes in crystals

Pallikara, Ioanna, Kayastha, Prakriti, Skelton, Jonathan M and Whalley, Lucy (2022) The physical significance of imaginary phonon modes in crystals. Electronic Structure, 4 (3). 033002. ISSN 2516-1075

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Abstract: The lattice vibrations (phonon modes) of crystals underpin a large number of material properties. The harmonic phonon spectrum of a solid is the simplest description of its structural dynamics and can be straightforwardly derived from the Hellman–Feynman forces obtained in a ground-state electronic structure calculation. The presence of imaginary harmonic modes in the spectrum indicates that a structure is not a local minimum on the structural potential-energy surface and is instead a saddle point or a hilltop, for example. This can in turn yield important insight into the fundamental nature and physical properties of a material. In this review article, we discuss the physical significance of imaginary harmonic modes and distinguish between cases where imaginary modes are indicative of such phenomena, and those where they reflect technical problems in the calculations. We outline basic approaches for exploring and renormalising imaginary modes, and demonstrate their utility through a set of three case studies in the materials sciences.

Item Type: Article
Additional Information: Funding information: IP is grateful to the University of Manchester (UoM) for the support of a PhD studentship. PK acknowledges support from the UK Engineering and Physical Sciences Research Council (EPSRC) CDT in Renewable Energy Northeast Universities (ReNU) for funding through EPSRC Grant EP/S023836/1. JMS is currently supported by a UK Research and Innovation (UKRI) Future Leaders Fellowship (MR/T043121/1), and previously held a UoM Presidential Fellowship.
Uncontrolled Keywords: Topical Review, phonons, anharmonicity, structure prediction, thermal properties
Subjects: F300 Physics
H600 Electronic and Electrical Engineering
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 19 Jul 2022 11:06
Last Modified: 19 Jul 2022 11:15

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