Journal Article Research Support, Non-U.S. Gov't relativistic quantum chemistry DFT functional Molecular integral NMR chemical shift accompanying coordinate expansion and recurrence relation method carbon atoms clustering composite model correlation energy density functional theory divide-and-conquer method electron repulsion integral electron-correlation theory energy fitting scheme extrapolation model general-contraction generalized Hartree-Fock heavy element hierarchical basis set high angular momentum isotope fractionation linear-scaling nuclear volume effect spin-dependent effect spin-free effect tensor contraction engine two-component relativistic framework two-component theory