Magneto-Electric response functions for simple atomic systems
  We consider a simple atomic two-body bound state system that is overall charge neutral and placed in a static electric and magnetic field, and calculate the magneto-electric response function as a function of frequency. This is done from first principles using a two-particle Hamiltonian for both an harmonic oscillator and Coulomb binding potential. In the high frequency limit, the response function falls off as 1/\omega^2 whilst at low frequencies it tends to a constant value. 
James Babington and Bart A. van Tiggelen
quant-ph physics.atom-ph