### Perturbation Calculation for Relativistic Energy Shift

Rewriting as we calculate the energy shift for a state . While there is no spin involved here, we will need to use these states for the spin-orbit interaction

where we can use some of our previous results.

Since this does not depend on either or , total states and the product states give the same answer. We will choose to use the total states, , so that we can combine this correction with the spin-orbit correction.

Jim Branson 2013-04-22