The intermediate-range order in molten and glassy GeSe<inf>2</inf>

The origin of the first sharp diffraction peak (FSDP), a characteristic of intermediate-range order in molten and vitreous chalcogenides, is studied in terms of interatomic potentials using the integral-equation method; GeSe2 is treated as a specific example. The following models with distinctive features are considered in a systematic way: (a) mixture of neutral hard spheres, (b) charged hard-sphere mixture, (c) system with a realistic potential; from (a) through (c), the size and charge-transfer effects are incorporated step by step. The rationale behind the FSDP proves to be cooperation of the excluded volume effect and the local charge neutrality leading to the conditional packing of atoms with formation of the tetrahedra, Ge(Se 1 2)4; the FSDP first appears at stage (b), i.e., in the model containing charged hard spheres. The validity and accuracy of the hypernetted-chain theory are also established through comparison with the exact molecular-dynamics results. © 1989.