Nuclear Spin–Spin Couplings: Efficient Evaluation of Exact Exchange and Extension to Local Hybrid Functionals

Abstract

We present an efficient implementation for the computation of nuclear spin-spin coupling tensors within density functional theory into the TURBOMOLE software suite. Emphasis is put on methods to efficiently evaluate the Hartree-Fock exchange needed for hybrid functionals: resolution of the identity and seminumerical evaluation on a grid. Our algorithm allows for the selection of specific nuclei for the reduction of calculation times. Further, the accuracy of locally dense basis sets in the density functional theory framework is investigated. These features allow for the routine computation of coupling constants in systems comprising about 100 carbon atoms within less than one day on a single CPU and within a few hours when using the OpenMP variant. Based on seminumerical integration, the first implementation of local hybrid functionals for spin-spin couplings is reported. This has allowed a preliminary evaluation of position-dependent exact-exchange admixture in three local hybrid functionals for a set of 80 isotropic spin-spin couplings in 23 small main-group molecules against CC3 and MCSCF reference data. Two of the local hybrids (LH14t-calPBE and LH07t-SVWN) are the top performers in the overall statistical evaluation compared to several standard functionals (TPSS, TPSSh, B3LYP, PBE0, and BHLYP), in particular, as they do not exhibit notable outliers for specific coupling types.