Electronic and structural properties of germania polymorphs

We present calculations for the electronic and structural properties of three polymorphs of ${\mathrm{GeO}}_2:$ the quartz, rutile, and coesite structures. The last structure is hypothetical. Although germania is not known to exist in the coesite structure, silica does. For this reason, we also include calculations for silica in the coesite structure to facilitate comparisons between the two oxides. Our calculations were performed within the pseudopotential density functional method, i.e., we used pseudopotentials constructed within the local density approximation and a plane wave basis. We determined the lattice parameters, cohesive energy, and bulk modulus by minimizing the total electronic energy of the solid. We find agreement for the structural properties within a few percent of experiment. The calculated electronic band structure, partial density, and total density of states are also presented. We find that for germania, in contrast to silica, the rutile structure is the lowest-energy polymorph.