Energy Continuity in Degenerate Density Functional Perturbation Theory
Materials Science
2016-07-22 v1 Chemical Physics
Quantum Physics
Abstract
Fractional occupation numbers can produce open-shell degeneracy in density functional theory. We develop the corresponding perturbation theory by requiring that a differentiable map connects the initial and perturbed states. The degenerate state connects to a single perturbed state which extremizes, but does not necessarily minimize or maximize, the energy with respect to occupation numbers. Using a system of three electrons in a harmonic oscillator potential, we relate the counterintuitive sign of first-order occupation numbers to eigenvalues of the electron-electron interaction Hessian.
Cite
@article{arxiv.1607.06404,
title = {Energy Continuity in Degenerate Density Functional Perturbation Theory},
author = {Mark C. Palenik and Brett I. Dunlap},
journal= {arXiv preprint arXiv:1607.06404},
year = {2016}
}