# Dresden 2017 – wissenschaftliches Programm

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# HL: Fachverband Halbleiterphysik

## HL 73: Electronic-Structure Theory: New Concepts and Developments in Density Functional Theory and Beyond - VI

### HL 73.10: Vortrag

### Donnerstag, 23. März 2017, 12:45–13:00, GER 38

**DFT meets Landau Theory: The High Pressure Phase Transition of Lead Titanate** — •Andreas Tröster — Vienna University of Technology, Institute of Material Chemistry, Getreidemarkt 9 A-1060 Wien, Austria

Landau theory (LT) coupled to infinitesimal strain is a cornerstone of the theory of structural phase transitions. At high pressures, however, this approach breaks down due to the appearance of large strains and the accompanying nonlinear elastic energy contributions. In density functional theory (DFT), on the other hand, stress and strain are easy to control, but entropic effects are difficult to incorporate since DFT is a genuine zero temperature method. Recently we have shown how to combine the strengths of these two antipodal approaches by constructing a high pressure extension of conventional LT with the help of DFT. Essential for the success of this approach is the ab initio calculation of pressure-dependent elastic constants. This theory yields a concise numerical description of the high pressure phase transition in strontium titanate, and also allows to resolve a number of severe and long-standing discrepancies between the experimental data and the theoretical description of the ferroelectric high pressure phase transition of the perovskite lead titanate, a material which is also of considerable technological interest.