THEORETICAL-STUDY OF MAGNETIC-PROPERTIES OF AMMONIA MOLECULE IN NONUNIFORM MAGNETIC-FIELD

The interaction Hamiltonian within the Bloch gauge for the potentials of the electromagnetic field has been used to define magnetic multipol e moment operators and operators for the magnetic field of electrons a cting on the nuclei of a molecule in the presence of nonhomogeneous ex ternal magnetic field. Perturbation theory has been applied to evaluat e the induced electronic moments and magnetic field at the nuclei. Mul tipole magnetic susceptibility and nuclear magnetic shielding tensors have been introduced to describe the contributions arising in nonunifo rm fields, and their origin dependence has been analyzed. Extended num erical tests on the ammonia molecule in a static, nonuniform magnetic field have been carried out, using the random-phase approximation with in the framework of accurate Hartree-Fock zero-order wavefunctions, an d allowing for both angular momentum and torque formalisms in the calc ulation of paramagnetic contributions.