Vibrational and thermal averaging of the indirect nuclear spin-spin coupling constants of CH4, SiH4, GeH4 and SnH4

Calculations of the indirect nuclear spin-spin coupling constants of PbH 4

“…The two perturbation-theory-based methods, SOPPA and SOPPA(CCSD), on the other hand increase the FC term by more than a factor of 4. This is consistent with results for the geminal coupling constants of SiH 4 , GeH 4 , and SnH 4 , where for a given X-H distance the 2 t H·H couplings obtained with SOPPA are markedly larger than those obtained from the RPA or any MCLR calculation [3]. Finally, the SD contribution as well as the other two [3] the CAS A and SOPPA coupling constant curves turned out to be nearly parallel.…”

“…The two perturbation-based methods, SOPPA and SOP-PA(CCSD), give results for 1 t Pb·H close to CAS A and CAS C, respectively. Most of the correlation contribution to 1 t Pb·H can thus be found using a valence CAS or SOPPA, which give the same sign and approximately the same magnitude, similar to what was found for the t (X·H) coupling constants of the other molecules in the XH 4 series [3]. From a comparison of the RPA and CAS A results, the SD term can be seen to be very sensitive to correlation; however its small size makes this fact unimportant.…”

“…Previous investigations [3,4] of the ZPVA corrections to the indirect nuclear spin±spin coupling constants in the XH 4 series showed that agreement with experiment cannot be expected without inclusion of ro±vibrational eects. In the present study we estimated the eect of nuclear motion by calculating the coupling constants for six dierent values of the totally symmetric stretching coordinate, since this is the only normal coordinate that contributes to the ro±vibrational averaging of the coupling constants in ®rst order.…”

“…The results included the random phase approximation (RPA) [1±3], the multicon®gurational linear-response (MCLR) method [1±3], the second-order polarization propagator approximation (SOPPA) [3], and SOPPA with coupled-cluster singles and doubles amplitudes SOPPA(CCSD) calculations [4] of all four contributions to the coupling constants. In addition, spin±orbit corrections were calculated at the RPA level [2] and ®rst-order estimates of ro±vibrational corrected and zero-point vibrational averaged (ZPVA) values of the coupling constants were evaluated at the RPA, MCLR, and SOPPA levels of approximation [3]. In the case of CH 4 second-order estimates of the ro± vibrational corrections to the coupling constants were also calculated at the SOPPA(CCSD) level [4].…”

The Spin–Spin Coupling Constants in Ethane, Methanol and Methylamine: A Comparison of DFT, MCSCF and CCSD Results

“…Third and perhaps most important, we have neglected the rovibrational contributions to the spin-spin coupling constants. Such contributions may be substantial for spin-spin coupling constants, which are sensitive to small changes in the geometry [21,22,34,35].…”