Dipole moments of molecules with multi‐reference character from optimally tuned range‐separated density functional theory

Dipole moment is the first nonzero moment of the charge density of neutral systems. If a density functional theory (DFT) method is able to yield accurate dipole moments, it should first provide an accurate geometry and then predict a reliable charge distribution for that geometry. In this respect, recent literatures have revealed that most DFT approximations work considerably better for single‐reference molecules with respect to multi‐reference ones, as may be expected from this fact that DFT utilizes a single configuration state function as reference function to represent the density. Putting together, it seems that as compared to the single‐reference systems, situation is slightly more involved in the case of dipole moment calculations of multi‐reference molecules. Effort to address this latter issue constitutes the cornerstone of the present investigation. To this end, we rely on a different approach where the new optimally (nonempirically) tuned range‐separated hybrid density functionals (OT‐RSHs) without invoking any empirical fitting are proposed for predicting the dipole moments of multi‐reference molecules containing both main‐group elements and transition metals. We have scanned the controlling factors of OT‐RSHs like short‐ and long‐range exchange contributions and range‐separation parameter with the aim of deriving the best performing models for the purpose. The obtained results unveil that, as compared to the standard range‐separated density functionals, our newly developed OT‐RSHs not only give an improved description on the dipole moments of the molecules with multi‐reference character but also the quality of their predictions is better than other conventional and recently proposed DFT approximations. © 2018 Wiley Periodicals, Inc.