electronic structure techniques, thereby allowing both We report a detailed computational investigation using sev-larger unit cells and a larger number of configurations to eral techniques relating to the phase transition from the ␣be examined. In a previous study (7), we applied these quartz to the rutile structure for GeO 2 and GeO 2 /SiO 2 solid techniques to the structures and stabilities of mixed Si/Ge solutions. We calculate an activation barrier of approximately and pure end member Ge analogs of microporous silicate 47 kJ mol ؊1 for the phase transition, which is in good agreement systems (8, 9). The present paper concentrates on the two with the most recently reported experimental value. We also dense phases, quartz and rutile. We exploit the ability of identify a number of interesting intermediate structures, in current computational techniques to perform calculations which Ge is present in two coordination environments (fourfold on large supercells (10) in order to derive atomistic models and sixfold). These complex intermediates have characteristics for the transition between the two phases. The success of akin to the experimentally observed amorphous systems. © 1996 our approach is shown by our calculation of an activation
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barrier that is in good agreement with the experimental value.