Abstract
Density functional theory with the local density approximation has been used to calculate Hellmann-Feynman forces for two chalcopyrite crystals: AgGaSe2 and AgGaTe2. Applying the direct method, phonons at all high-symmetry points of the chalcopyrite structure have been obtained. The results are in very good agreement with experimental data from Raman, infrared, and inelastic neutron scattering.
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