Perturbation Calculation for Relativistic Energy Shift
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
states and the product
states give the same answer.
We will choose to use the total
, so that we can combine this correction
with the spin-orbit correction.