Instantaneous normal modes analysis of amorphous and supercooled silica

The dynamics of a model for amorphous and supercooled silica (SiO2), a strong glass former, is studied using instantaneous normal mode (INM) analysis. The INM spectra at a variety of temperatures are calculated via molecular dynamics simulation. At temperatures below the glass transition temperature, the dominant contribution to the soft highly anharmonic modes comprising the imaginary frequency region of the INM spectrum are found to correspond to coupled rotations of SiO4 tetrahedral units, consistent with interpretations of neutron scattering experiments [B. B. Buchenau, H. M. Zhou, and N. Nucker, Phys. Rev. Lett. 60, 1318 (1988)] and with previous normal mode analysis of simulation results at T=0 K [S. N. Taraskin and S. R. Elliot, Phys. Rev. B 56, 8623 (1997)]. (C) 2001 American Institute of Physics.