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.