Disorder-robust bands from anisotropic orbitals in a coordination polymer semiconductor.

While the effects of structural disorder on the electronic properties of solids are poorly understood, it is widely accepted that spatially isotropic orbitals lead to robustness against disorder. In this paper, we use first-principles calculations to show that a cluster of occupied bands in the coordination polymer semiconductor β-copper(I) thiocyanate undergo relatively little fluctuation in the presence of thermal disorder-a surprising finding given that these bands are composed of spatially anisotropic d-orbitals. Analysis with the tight-binding method and a stochastic network model suggests that the robustness of these bands to the thermal disorder can be traced to the way in which these orbitals are aligned with respect to each other. This special alignment causes strong inverse statistical correlations between orbital-orbital distances, making these bands robust to random fluctuations of these distances. As well as proving that disorder-robust electronic properties can be achieved even with anisotropic orbitals, our results provide a concrete example of when simple 'averaging' methods can be used to treat thermal disorder in electronic structure calculations.