The Hamiltonian for a single spin S and its interaction with the magnetic field is in general a sum of terms with , with pB and pS non-negative integers. pB +pS has to be even to fulfill time-reversal invariance. Only terms with pS ≤ 2S are effective. Mc Gavine et al. formulated such general spin Hamiltonian using tesseral harmonics. Advantages are the following:
Next we will derive the coefficients for Hamiltonian's widely used in spin physics.