Yuheng Liu with Walter Lambrecht

Study of the vibrational modes in BeSiN₂ and BeGeN₂

The heterovalent, ternary, II-IV-N₂ compounds BeGeN₂ and BeSiN₂ are related to GaN. Conceptually, one can replace two of the four group-III cations surrounding each nitrogen anion by a group II element, and the other two by a group-IV element.   Only their lattice constants are known. The vibrational properties of BeGeN₂ and BeSiN₂ can be measured by the Raman spectra and infrared absorption or reflection spectra and calculated by density functional perturbation theory. In this project, the density functional theory will be used  to determine the equilibrium structure and the force constants related to small displacements of the atoms from their equilibrium and from them the normal mode frequencies will be obtained. These will be used to simulate Raman and infrared spectra, which could be compared with experiments if such measurements become available. The symmetry character of the vibrational normal modes will be identified using group theory.