Ionicity in disordered GeSe2: a comparison of first-principles and atomistic potential models.

The structural properties of liquid GeSe(2), generated using two distinct computational methodologies, are compared. The results of molecular dynamics simulations, utilizing both first-principles density functional and a potential model which account for aspects of many-body interactions, are considered. The potential model favors ionic character in the bonding, resulting in a structure with very little chemical disorder and no homopolar bonds, in contrast to experimental observation. The use of a relatively simple potential model is shown to be useful in order to understand differences between the observed experimental structure and those obtained from the first-principles approach, the latter being affected by insufficient account of ionic character in the bonding. Both computational schemes are able to predict the appearance of the first sharp diffraction peak in the total neutron structure factor and in some of the partial structure factors as well as the concomitant presence of corner- and edge-sharing tetrahedral connections. For the potential model, this holds true provided the system temperatures are set to values high enough to allow for diffusion properties typical of a liquid. Structural properties obtained for the two sets of configurations are in closer agreement when the potential model is applied at very high temperatures.

The evolution of intermediate-range order in molten network-forming materials.

The atomistic origin of the intermediate-range order (IRO) is investigated for an archetypal network-forming liquid. A pairwise additive potential model is chosen which is augmented with a description of the (many-body) anion polarization. The anion polarizability and system temperature are both systematically varied in order to control the network topology. The change in the IRO is monitored via the construction of Bhatia-Thornton structure factors which highlight the effect of chemical composition and network topology. The atomistic origin of the first-sharp diffraction peak in the concentration-concentration function, S(CC)(k), is discussed in terms of the connectivity of the polyhedral network. The atomistic origin of the IRO is discussed by reference to previous analyses.