Faculty Advisor

L. R. Ram-Mohan

Faculty Advisor

Padmanabhan K. Aravind

Faculty Advisor

Richard D. Sisson, Jr.

Abstract

The dispersion relation between frequency and wavevector of atomic vibrations, or phonons, can be succinctly described by the adiabatic bond charge model, first developed by Weber. The model employs as few as four parameters to fit experiment. We investigated this model in order to better unify the description of the technologically relevant group IV elemental semiconductors (e.g. diamond, silicon, germanium, and gray tin) by replacing an ad hoc parameter introduced by Weber with one arising from quadrupolar interactions between the bond charges, and by fitting the parameters to density functional theory calculations. We also illustrate constant frequency surfaces embedded in wavevector space for the various modes of vibration for the first time. The bond charge model allows for rapid calculation of various quantities related to the interaction of phonons with electrons and photons as compared to density functional theory, especially in structures with little symmetry and for macroscopic structures, thus enabling the design of complicated electronic and photonic devices much more accurately.

Publisher

Worcester Polytechnic Institute

Degree Name

PhD

Department

Physics

Project Type

Dissertation

Date Accepted

2012-04-26

Accessibility

Unrestricted

Subjects

sound, solid state physics, phonons, quantum mechanics

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