Implementation and Validation of Constrained Density Functional Theory Forces in the CP2K Package

Constrained density functional theory (CDFT) is a powerful tool for the prediction of electron transfer parameters in condensed phase simulations at a reasonable computational cost. In this work we present an extension to CDFT in the popular mixed Gaussian/plane wave electronic structure package CP2K, implementing the additional force terms arising from a constraint based on Hirshfeld charge partitioning. This improves upon the existing Becke partitioning scheme, which is prone to give unphysical atomic charges. We verify this implementation for a variety of systems: electron transfer in (H2O)(2)(+) in a vacuum, electron tunnelling between oxygen vacancy centers in solid MgO, and electron self-exchange in aqueous Ru2+-Ru3+. We find good agreement with previous plane-wave CDFT results for the same systems, but at a significantly lower computational cost, and we discuss the general reliability of condensed phase CDFT calculations.

Automated summary

Constrained density functional theory (CDFT) is a powerful tool for predicting electron transfer parameters in condensed phase simulations. In this study, an extension to CDFT is presented in the popular electronic structure package CP2K, implementing additional force terms based on Hirshfeld charge partitioning. The improved method shows good agreement with previous results at a lower computational cost, and the general reliability of condensed phase CDFT calculations is discussed.