Implementation of nuclear gradients of range‐separated hybrid density functionals and benchmarking on rotational constants for organic molecules

We have implemented the nuclear gradient for several range‐separated hybrid density functionals in the general quantum chemistry code ORCA. To benchmark the performance, we have used a recently published set of back‐corrected gas phase rotational constants, which we extended by three molecules. In our evaluation, CAM‐B3LYP‐D3 and ωB97X‐D3 show great accuracy, and are surpassed by B2PLYP‐D3 only. Lower‐cost alternatives to quadruple‐ζ basis set‐based calculations, among them a smaller basis set and the use of resolution‐of‐the‐identity approaches, are assessed and shown to yield acceptable deviations. In addition, the Hartree‐Fock‐based back‐correction method is compared to a density functional theory alternative, which largely shows consistency between the two. A new, well‐performing, spin‐component scaled MP2 variant is designed and discussed, as well. © 2014 Wiley Periodicals, Inc.