Transmission of the spin-spin coupling constants through hydrogen bonds in ammonia clusters

Spin-spin coupling constants are reported using six ab initio and fifteen DFT methods for dimers and larger clusters of ammonia. An analysis of components (Fermi contact, spin dipole, paramagnetic spin-orbit, and diamagnetic spin-orbit) of more relevant coupling constants 1JNH′, 1hJNH′ and 2hJNN has been carried out. Fermi contact is the dominant term in the total value for all constants. For dimers, a relationship between the addition of direct and intermolecular coupling constants gives the direct constants of monomer. From the comparison of all ab initio and DFT methods for dimers, SOPPA(CCSD) and S55VWN5 methods are, respectively, more reliable taking into account their accuracy and the computing time. Both methods are employed for the analysis of the transmission of coupling constants through the hydrogen bond for ammonia clusters. A linear relation between the intermolecular constants 1hJNH′ and the length of the hydrogen bond is found.