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 xB97X-D3 show great accuracy, and are surpassed by B2PLYP-D3 only. Lower-cost alternatives to quadruple zeta 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. (C) 2014 Wiley Periodicals, Inc.