MOLECULAR-DYNAMICS SIMULATION OF NUCLEAR-SPIN RELAXATION OF LI-7(+) IN WATER

The nuclear spin relaxation of (7)L(+) in water has been studied by molecular dynamics simulations. The effects of both the dipole-dipole and the quadrupolar relaxation mechanism were calculated. The protons in water are the main sources of the dipole-dipole interaction, but the relaxation due to O-17 is also studied. In addition, the cross-correlation between the dipole-dipole and the quadrupolar interactions is discussed. Simulations at different temperatures were performed, in order to examine the temperature dependence in the relaxation rates. The agreement with experiment for dipole-dipole relaxation is good, whereas the quadrupole relaxation is found to be more difficult to simulate. Both mechanisms are analysed in terms of molecular motions. Comparison with theoretical models for quadrupole relaxation shows that the solvent can be modelled as a collection of radially oriented electric dipoles.