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MM: Fachverband Metall- und Materialphysik

MM 30: Methods in Computational Materials Modelling III: Thermodynamics

MM 30.2: Talk

Wednesday, March 18, 2015, 10:30–10:45, H 0106

Phonon modes in Binary Crystals with Positional Disorder — •Tadeus Ras and Matthias Fuchs — Fachbereich Physik, Universität Konstanz, 78457 Konstanz

Classical DFT relates equilibrium density fluctuations δρ(q) to elastic response [1]. We present the dispersion relations of binary crystals following an approach to crystal elasticity that
includes positional disorder [2].

Even a simple Ramakrishnan-Youssouf DFT of binary hard sphere systems predicts a variety of crystalline phases such as disordered fcc [3]. We illustrate the computation of both acoustical and optical phonon eigenfrequencies ω(q) of these phases in the presence of point defects. Further we point out the link of ω(q) to mechanical instabilities that may lead to martensitic phase transitions.

ω(q) can also be derived from the fluctuations δρ(q) itself. We finally refer to a straighforward method of evaluating experimental or simulation positional data.

M. Fuchs, ’Elastic properties of colloidal solids with disorder’,

Proceedings of the International School ’Enrico Fermi’ (2013).
C. Walz and M. Fuchs, Phys. Rev. B, 81 (2010) 134110.
S. W. Rick and A. D. J. Haymet, J. Phys. Chem., 94 (1990) 5212.