Localized molecular orbital analysis of the effect of electron correlation on the anomalous isotope effect in the NMR spin-spin coupling constant in methane

TY - JOUR

T1 - Localized molecular orbital analysis of the effect of electron correlation on the anomalous isotope effect in the NMR spin-spin coupling constant in methane

AU - Zarycz, M. Natalia C.

AU - Sauer, Stephan P. A.

AU - Provasi, Patricio F.

PY - 2014/10/21

Y1 - 2014/10/21

N2 - We discuss the effect of electron correlation on the unexpected differential sensitivity (UDS) in the 1J(C-H) coupling constant of CH4 using a decomposition into contributions from localized molecular orbitals and compare with the 1J(N-H) coupling constant in NH3. In particular we discuss the well known fact that uncorrelated coupled Hartree-Fock (CHF) calculations are not able to reproduce the UDS in methane. For this purpose we have implemented for the first time a localized molecular orbital analysis for the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes - SOPPA(CCSD) in the DALTON program. Comparing the changes in the localized orbital contributions at the correlated SOPPA and SOPPA(CCSD) levels and at the uncorrelated CHF level, we find that the latter overestimates the effect of stretching the bond between the coupled atoms on the contribution to the coupling from the localized bonding orbital between these atoms. This disturbs the subtle balance between the molecular orbital contributions, which lead to the UDS in methane.

AB - We discuss the effect of electron correlation on the unexpected differential sensitivity (UDS) in the 1J(C-H) coupling constant of CH4 using a decomposition into contributions from localized molecular orbitals and compare with the 1J(N-H) coupling constant in NH3. In particular we discuss the well known fact that uncorrelated coupled Hartree-Fock (CHF) calculations are not able to reproduce the UDS in methane. For this purpose we have implemented for the first time a localized molecular orbital analysis for the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes - SOPPA(CCSD) in the DALTON program. Comparing the changes in the localized orbital contributions at the correlated SOPPA and SOPPA(CCSD) levels and at the uncorrelated CHF level, we find that the latter overestimates the effect of stretching the bond between the coupled atoms on the contribution to the coupling from the localized bonding orbital between these atoms. This disturbs the subtle balance between the molecular orbital contributions, which lead to the UDS in methane.

U2 - 10.1063/1.4897625

DO - 10.1063/1.4897625

M3 - Journal article

SN - 0021-9606

VL - 141

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

IS - 15

M1 - 151101

ER -