# Multipole expansions

AngularMomentumAlgebra.multipole_expand_scalar_productFunction
multipole_expand_scalar_product(a, b, P, Q, c, d)

Multipole-expand the matrix element ⟨ab|P⋅Q|cd⟩, where the tensor P acts on orbitals a & c, and the tensor Q acts on orbitals b & d. The definition is taken from Eq. (13.1.26) of Varshalovich (1988).

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