@article {10,
	title = {Analytical derivatives of the individual state energies in ensemble density functional theory method. I. General formalism},
	journal = {J. Chem. Phys.},
	volume = {147},
	year = {2017},
	pages = {034113},
	chapter = {034113},
	doi = {https://doi.org/10.1063/1.4994542},
	url = {https://aip.scitation.org/doi/abs/10.1063/1.4994542},
	author = {Filatov, Michael and Liu, Fang and Todd J. Mart{\'\i}nez}
}