First-principles study of structural, elastic, electronic and optical properties of rutile GeO2 and α-quartz GeO2

Structural parameters, elastic, electronic, bonding and optical properties of rutile GeO2 and alpha-quartz GeO2 have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. Two phases of GeO2 are found to be elastically stable and we have derived the bulk, shear and Young's modulus, Poisson coefficient for rutile GeO2 and alpha-quartz GeO2. We estimated the Debye temperature of rutile GeO2 and alpha-quartz GeO2 from the acoustic velocity. Electronic and chemical bonding properties have been studied from the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for rutile GeO2 and alpha-quartz GeO2, the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and the complex conductivity function are calculated, which show the significant optical anisotropy in the components of polarization directions (100) and (001) for rutile GeO2 and alpha-quartz GeO2. (C) 2010 Elsevier Masson SAS. All rights reserved.