Hi PF members. I have got a little worry I am familiar with the Zeeman term that always appears in the Hamiltonian of a spin chain representing the influence of an external magnetic field. I don't know if there is a similar term if the spin was rather in he presence of an electric field ( I just think if the electric field has effects on the spin, then those effects would be as important as those of the magnetic field). I have not come across any good literature on this. could some one point me in the right direction?