From the change in kinetic energy induced by an external field, we discuss the applicable conditions for the Mott-Davis and Moseley-Lukes form of the Kubo-Greenwood formula (KGF) for the electrical conductivity which has been implemented in \textit{ab initio} codes. We show that the simplified KGF is suitable only for computing the AC conductivity at sufficiently high frequency and when the gradient of the carrier density is small.
Cite
@article{arxiv.1011.4113,
title = {The Work Done by an External Field},
author = {Mingliang Zhang and D. A. Drabold},
journal= {arXiv preprint arXiv:1011.4113},
year = {2010}
}