SIMPLE, THEREFORE REALISTIC: MAKING MODELS OF a-SI

Structural Simplicity as a Constraint on the Structure of Amorphous Silicon
M J Cliffe, A P Bartók, R N Kerber, C P Grey, G Csányi, and A L Goodwin
arxiv:1609.00668 (2016)

Determining the structural origins of the properties of amorphous materials remains one of the most important challenges in structural science. In this Letter we demonstrate that local ‘structural simplicity’, embodied by the degree to which atomic environments within a material are similar to each other, can provide a valuable constraint on the structures of amorphous materials. We show, for the exemplar noncrystalline material amorphous silicon (a-Si), that the characteristic flaw of data-driven modelling techniques – their tendency to introduce excess structural complexity – can be ameliorated by using simplicity as a constraint, allowing for models approaching those of the state-of-the-art to be produced through refinement against the pair distribution function (PDF). A further consequence of this simplicity is the creation of realistic electronic structure. We also demonstrate that ab initio minimisation of data-driven models increases their simplicity, and improves their atomic and electronic structures to a quality that approaches that of current state-of-the-art models of a-Si. The generality of this approach suggests it could be used for the refinement of the structures of a wide variety of amorphous materials.