Computer simulation study of low-energy excitations of silicate glasses

Ten silicate and aluminosilicate glasses with different number densities and connectivities were studied by molecular dynamics simulation using the computer program DL-POLY [1]. The radial distribution functions, phonon densities of states and flexibilities of the glass networks were determined, and compared with those determined for silica [2]. The large-scale flexibility of silica was found to be similar to that of some of the glasses studied in this work, particularly in relation to rigid-unit-mode-type motions. The degree of localization of vibrations in fully networked glasses was found to be similar to that in silica, but the vibrations in glasses containing non-bridging oxygen atoms were found to be more localized. This is thought to be due to clustering of alkali cations, which in turn necessarily produces clusters of tetrahedra.