Modeling noncrystalline materials: Use of vibrational spectra as a protocol for validation

Abstract

Noncrystalline materials are important systems that can be investigated by molecular dynamics (MD); the constant improvement of computing capacity and speed makes it possible to employ MD simulations for the derivation of fundamental macroscopic properties from microdynamics. Hydrogenated amorphous silicon represents a good test material for simulation due to the extensive literature on its optoelectronic properties, and many variants of MD have been attempted to describe this material and to obtain information on its macroscopic properties. As MD is increasingly used to characterize noncrystalline materials, it is crucial to verify that the numerical model is consistent with experimental data. However, in most cases the only derived property used to test the ``realism'' of the models has been the radial distribution function (RDF). We report extensive ab initio simulation of hydrogenated amorphous silicon that demonstrates that, although agreement with the RDF is a necessary requirement, this protocol is insufficient for the validation of a model; we show that the derivation of realistic vibrational spectra is a more efficient and valid protocol to ensure the reproducibility of macroscopic experimental features.