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MM: Fachverband Metall- und Materialphysik

MM 41: Methods in Computational Materials Modelling I: Ab initio thermodynamics

MM 41.5: Talk

Wednesday, March 9, 2016, 17:00–17:15, H52

Intricacies of phonon line shapes in random alloys: A first-principles study — •Biswanath Dutta¹, Debashish Das², Subhradip Ghosh², Biplab Sanyal³, Tilmann Hickel¹, and Jörg Neugebauer¹ — ¹Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany — ²Department of Physics, IIT Guwahati, Guwahati 781039, India — ³Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden

Lattice vibrations in random alloys are governed by the amount of mass and force-constant disorder present in the system. Disorder-induced scattering in these systems results in broadening of phonon peaks, which can be asymmetric and (for extreme disorder) can even split into two branches. To calculate phonon frequencies, lifetimes, as well as the complex phonon line shapes, sophisticated modeling approaches are required. We use the itinerant coherent potential approximation (ICPA), a Green's function based formalism to account for local fluctuations in random alloys. The interatomic force-constants are calculated using density functional theory and are fed into ICPA to perform the configuration averaging. Our computed results for Cu-Au and Ni-Pt alloys show that a single Lorentzian function cannot describe the phonon line shapes for several wave-vectors. The comparison between theory and experiment also depends on the choice of the Lorentzian function. We discuss the results in the framework of phonon line shape convolution and conclude that multiple Lorentzian fitting for certain wave-vectors in random alloys gives new insights on phonon frequencies and their line widths which can be relevant for their functional properties.