Manu: polished the conclusion

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Emmanuel Fromager 2020-02-28 09:59:41 +01:00
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\section{Concluding remarks} \section{Concluding remarks}
\label{sec:conclusion} \label{sec:conclusion}
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In the present article, we have constructed a local, weight-dependent three-state DFA in the context of ensemble DFT.
The KS-eLDA scheme delivers accurate excitation energies for both single and double excitations, especially within its state-averaged version where the same weights are assigned to each state belonging to the ensemble.
Generalization to a larger number of states is straightforward and will be investigated in future work.
We have observed that, although the derivative discontinuity has a non-negligible effect on the excitation energies (especially for the single excitations), its magnitude can be significantly reduced by performing state-averaged calculations instead of zero-weight calculations.
Using similar ideas, a three-dimensional version \cite{Loos_2009,Loos_2009c,Loos_2010,Loos_2010d,Loos_2017a} of the present eDFA is currently under development to model excited states in molecules and solids. A local and ensemble-weight-dependent correlation density-functional approximation
Similar to the present excited-state methodology for ensembles, one can easily design a local eDFA for the calculations of the ionization potential, electron affinity, and fundamental gap. \cite{Senjean_2018} (eLDA) has been constructed in the context of GOK-DFT for spin-polarized
This can be done by constructing DFAs for the one- and three-electron ground state systems, and combining them with the two-electron DFA in complete analogy with Eqs.~\eqref{eq:ec} and \eqref{eq:ecw}. triensembles in
We hope to report on this in the near future. 1D. The approach is actually general and can be extended to real
(three-dimensional)
systems~\cite{Loos_2009,Loos_2009c,Loos_2010,Loos_2010d,Loos_2017a}
and larger ensembles in order to
model excited states in molecules and solids. Work is currently in
progress in this direction.
Unlike any standard functional, eLDA incorporates derivative
discontinuities through its weight dependence. The latter originates
from the finite uniform electron gas eLDA is
(partially) based on. The KS-eLDA scheme, where exact exchange is
combined with eLDA, delivers accurate excitation energies for both
single and double excitations, especially when an equiensemble is used.
In the latter case, the same weights are assigned to each state belonging to the ensemble.
{\it We have observed that, although the derivative discontinuity has a
non-negligible effect on the excitation energies (especially for the
single excitations), its magnitude can be significantly reduced by
performing state-averaged calculations instead of zero-weight
calculations.}\manu{to be updated ...}
Let us finally stress that the present methodology can be extended
straightforwardly to other types of ensembles like, for example, the
$N$-centered ones, thus allowing for the design an LDA-type functional for the
calculation of ionization potentials, electron affinities, and
fundamental gaps. \cite{Senjean_2018,Senjean_2020}.
Like in the present
eLDA, such a functional would incorporate the infamous derivative
discontinuity contribution to the gap through its explicit weight
dependence. We hope to report on this in the near future.
\trashEF{This can be done by constructing a functional for the one- and
three-electron ground-state systems, and combining them with the
two-electron DFA in complete analogy with Eqs.~\eqref{eq:ec} and
\eqref{eq:ecw}.}\manu{I find the sentence too technical for a
conclusion.}
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\section*{Supplementary material} \section*{Supplementary material}