HNC theory of medium-range order in glasses

The first sharp diffraction peak (FSDP) and its anomalous temperature dependence, characterizing medium-range order in molten and vitreous chalcogenides, are elucidated in terms of interatomic potentials using the integral-equation method. The systematic study of the size and charge-transfer effects in GeSe2 shows that the rationale behind the FSDP is 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 anomaly in the FSDP is ascribed to the increase of the number density on cooling. © 1988.