Dependence of Nonadiabatic Couplings with Kohn-Sham Orbitals on the Choice of Density Functional: Pure vs Hybrid

Nonadiabatic molecular dynamics (NA-MD) is an extremely useful approach to model electron transfer dynamics in molecular and solid state systems. The performance of NA-MD simulations depends critically on the accuracy of the underlying electronic structure properties, such as state energies and nonadiabatic couplings (NAC). Practical NA-MD modeling relies extensively on computationally efficient pure density functionals, despite the known intrinsic problems of the latter. A reliable solution to the problems presented by the use of pure density functionals, is the use of hybrid functionals, however hybrid functionals are significantly more expensive. In this work, we investigate how the choice of the density functional can affect the NAC magnitudes for small silicon clusters and silicon hydrides. We find that pure functionals can significantly overestimate NAC magnitudes in comparison to those obtained with hybrid functionals. The ratio of the two magnitudes increases with the system size and differs by an order of magnitude even for small Si7 and Si26 clusters. We present a detailed analysis of the correlations of the NACs computed with different methods, discuss the fundamental grounds for the observed differences, and propose a simple scaling technique for correcting NACs that can be used within the context of NA-MD simulations.