  Force-constant and positional disorder have been introduced into diamond
lattice models in an attempt to mimic the vibrational properties of a realistic
amorphous silicon model. Neither type of disorder is sufficient on its own to
mimic the realistic model. By comparing the spectral densities of these models,
it is shown that a combination of both disorders is a better representation,
but still not completely satisfactory. Topological disorder in these models was
investigated by renumbering the atoms and examining the dynamical matrix
graphically. The dynamical matrix of the realistic model is similar to that of
a positionally-disordered lattice model, implying that the short-range order in
both systems is similar.
