Laplace expansion (potential)

In physics, the Laplace expansion of potentials that are directly proportional to the inverse of the distance (${\displaystyle 1/r}$), such as Newton's gravitational potential or Coulomb's electrostatic potential, expresses them in terms of the spherical Legendre polynomials. In quantum mechanical calculations on atoms the expansion is used in the evaluation of integrals of the inter-electronic repulsion.