Structural, elastic, and mechanical properties of germanium dioxide from first-principles calculations

The structural, elastic, and mechanical properties of the available experimental and theoretical phases of germanium dioxide (GeO2) are investigated. Germanium dioxide (GeO2) is an important material in science and technology due to its wide-ranging applications, and many researches have been proposed to investigate its crystalline polymorphs. Although many phases have been reported, the systematic analysis and comparison of various phases are still lacking. In our paper, the energy, structural, elastic, mechanical properties and mechanical stability of the available experimental and theoretical phases of GeO2 are investigated from first-principles within the density-functional theory (DFT) plus the local density approximation. The order of increasing ground-state energy is as follows: P42/mnm, Pnnm, P21/c, Pbcn, Pnma, P3221 (P3121), P41212, C2/c, P63/mmc  , Pa3¯, P4/mcc, P6222, C2221, Pn3¯m and P6¯2m, indicating that tetragonal P42/mnm phase and hexagonal Fe2P-type P6¯2m phase have minimum and maximal ground-state energy, respectively. The structural parameters, elastic constants, bulk modulus, shear modulus, Young׳s modulus, Poisson׳s ratio, Lamé׳s constants as well as mechanical stability have been obtained and discussed, indicating that P6222 and P6¯2m phases are unstable under zero pressure. These results may help to understand GeO2 for future applications.