On the Origin of Spin-Hamiltonian Parameters

Abstract

The various coupling constants which appear in the phenomenological spin Hamiltonian for an atom or molecule can, in principle, be determined from a knowledge of the electronic wavefunction. It is difficult to obtain a physical picture of their origin and interrelationship because of the complexity of the many‐electron wavefunction. The problem may be greatly simplified by introducing certain standard density functions, of which the ``spin density'' is the most familiar. Only three types of function are required, all with a physical meaning which is readily visualized. Their significance in determining spin‐Hamiltonian parameters is discussed and illustrated with reference to (i) hyperfine coupling (contact and dipole—dipole), (ii) nuclear spin—spin coupling, (iii) electron spin—spin coupling, (iv) g values.