Electron correlation effects on the theoretical calculation of nuclear magnetic resonance spin–spin coupling constants

Abstract

The equation-of-motion coupled cluster singles and doubles (EOM-CCSD) method for general second-order properties is derived providing a quadratic, CI-like approximation and its linked form from coupled cluster (CC) energy derivative theory. The effects of the quadratic contribution, of the atomic basis set employed, and of electron correlation on NMR spin–spin coupling constant calculations using EOM-CCSD methods are investigated for a selected set of difficult molecules, notably CH3F, B2H6, CH3CN, C2H4, and CH3NH2. We find that the quadratic contribution is insignificant for the couplings in the molecules considered in this study and in addition the quadratic contribution only slightly depends on the basis set used. Therefore it seems well justified to use the less expensive CI-like approximation or its linked-diagram form to evaluate spin–spin coupling constants. The Fermi-contact contribution shows the largest variation with the change of basis sets. The diamagnetic spin–orbit (DSO) and the spin–dipole (SD) contribution vary little, seemingly being converged at the DZP level while the paramagnetic spin–orbit (PSO) term shows moderate variations. Except for very few cases, the FC contribution is dominant in all the couplings in the selected set of molecules and it is also most sensitive to the inclusion of electron correlation. The other contributions are less affected by electron correlation. Although of lesser importance, the significance of the noncontact contributions and electron correlation effects on accurate calculation of coupling constants such as 1J(13C19F) in CH3F and 1J(13C15N) in CH3CN is clearly demonstrated.

Using beryllium bonds to change halogen bonds from traditional to chlorine-shared to ion-pair bonds

“…39 Since MP2 orbitals do not exist, charge-transfer energies were obtained using the B3LYP functional 40,41 with the aug 0 -cc-pVTZ basis set at the MP2/aug 0 -cc-pVTZ geometries, so that at least some electron correlation effects could be included. Spin-spin coupling constants were evaluated using the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) method in the CI(configuration interaction)-like approximation, 42,43 with all electrons correlated. For these calculations, the Ahlrichs 44 qzp basis set was placed on 13 C, 15 N, and 19 F, and the qz2p basis set on 35 Cl.…”

H2XP:OH2 Complexes: Hydrogen vs. Pnicogen Bonds

“…Spin-spin coupling constants were evaluated using the EOM-CCSD method in the CI (configuration interaction)-like approximation [39,40], with all electrons correlated. For these calculations, the Ahlrichs [41] qzp basis set was placed on 13 C, 15 N, 17 O, and 19 F, and the qz2p basis set on 31 P, 35 Cl, and hydrogen-bonded 1 H atoms.…”

Solvent Effects on the Indirect Spin–Spin Coupling Constants of Benzene: The DFT-PCM Approach

“…The triplet nature of the Fermi-contact and the spin-dipolar operators means that ordinary spin-restricted approaches such as Hartree-Fock fails completely, often giving results that are several order of magnitudes too large as well as having incorrect signs [7,8]. The problem of triplet instabilities is often quite efficiently solved by introducing electron correlation, and several successful studies using multiconfigurational self-consistent field (MCSCF) [7,[9][10][11] or coupled-cluster [12][13][14] wave functions have been presented. An alternative approach has used the second-order polarization propagator approximation (SOPPA) [2,15].…”