Irreducible tensor operator methods in intermediate‐field coupling

The algebra of irreducible tensor operators is developed in the intermediate‐field coupling case. The Wigner‐Eckart theorem is formulated for a simple irreducible tensor operator as well as for the Kronecker and scalar products of these operators. The expressions required for the calculation of Coulomb repulsion, crystal field splitting, spin‐orbit interaction, and Zeeman effect are given in detail. Recent applications to various problems in spectroscopy and magnetism of transition metal compounds are referred to.