# A Genkin-Mednis Method? An extra term -- why?

1. Mar 27, 2017

### PRB147

The Genkin-Mednis is usually used to calculate the nonlinear optical properties of periodic polymers or crystals, the analytical derivation is captured in the posted image,

My problem is (483), where does an extra term on the right hand side of (483)
come from? $$ie S^\dagger (\kappa t)\nabla_{\kappa} S^\dagger (\kappa t) E(t)$$
My derivation is simple:
left multiplying $$S^\dagger$$ in the last equation in page 197
Then we can derive (483) but without the extra term $$ie S^\dagger (\kappa t)\nabla_{\kappa} S^\dagger (\kappa t) E(t)$$, Who can give me a hint, why the extra term appears?

2. Apr 1, 2017

### PF_Help_Bot

Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.