First principles modeling of intermediate range order in amorphous SiSe2

The structural properties of amorphous SiSe2 are studied by performing extensive first-principle molecular dynamics simulations. Comparison with experiments in terms of total neutron scattering factor and nuclear magnetic resonance data confirms the reliability of our model. Partial pair correlation functions and ring statistics are used to identify the structural units whose spatial organization gives raise to the intermediate range order. An accurate analysis reveals that amorphous SiSe2 is largely a chemically ordered system consisting mainly of a network of silicon centered tetrahedra. Different types of connections among the tetrahedra can be identified and classified. In particular edge-sharing connections seem to play a fundamental role in the establishment of the intermediate range order and in the appearance of the first sharp diffraction peak in the total neutron scattering factor.