1. The problem statement, all variables and given/known data Using the explicit expression for the mulitpolar polarization, find the matrix elements <2s | P(r) | 1s> of the microscopic polarization between the 1s and 2s states of the hydrogen atom. 2. Relevant equations [tex]P(r) = \int dr' r' \rho(r') \delta(r-r')[/tex] I don't understand how the Dirac Delta Function is supposed work? What it is and how does it operate in the intergral? 3. The attempt at a solution [tex]<\psi(2s) | P(r) | \psi(1s) = \int dr' r' \rho(r') \delta(r-r')[/tex] [tex]\psi(1s), \psi(2s)[/tex] are just H-atom wavefunctions.