The microscopic origin of anomalous thermodynamics and transport properties in tetrahedral network forming oxides such as water, silica, and GeO<sub>2</sub> has attracted significant research efforts, yet remains the subject of controversy. The existing theories predominantly invoke tetrahedral structure considerations to explain the anomalous properties of the network forming oxides. In this work we present the first direct simulation evidence of the existence of core-softening in the oxygen subsystem of silica and reveal its important role in forming the anomalous behavior of the silica, thus providing a link to similar anomalous phenomena observed in core-softening compounds lacking tetrahedral structure, such as liquid metals. We describe a soft-core interatomic force field for silica recently reported by us [J. Chem. Phys. <b>136</b>, 134508 (2012)] augmented to include three-body forces. The derived shape of the three-body potential term affirms the existence of repulsion softening between oxygen atoms at short separations. By comparing the soft-core model and a similar model with the soft-core suppressed, we demonstrate that the topology reorganization within the local tetrahedral network and the O-O core-softening are two competitive mechanisms responsible for anomalous thermodynamic and kinetic behaviors observed in liquid and amorphous silica. We show that the O-O core-softened interaction enhances the observed anomalies primarily through two mechanisms: facilitating the defect driven structural rearrangements of the silica tetrahedral network and modifying the tetrahedral ordering induced interactions toward multiple characteristic scales, the feature which underlies the thermodynamic anomalies.

Core-softened potentials for modelling the anomalous properties of silica

251st National Meeting (2016)

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