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@ -137,13 +137,13 @@ ensemble correlation energies}}
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We report a local, weight-dependent correlation density-functional approximation that incorporates information about both ground and excited states in the context of density-functional theory for ensembles (eDFT).
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This density-functional approximation for ensembles is specially
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designed for the computation of single and double excitations within
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Gross--Oliveira--Kohn (GOK) DFT (\textit{i.e.}, eDFT for \manu{neutral
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excitations} \trashEF{excited states}), and can be seen as a natural extension of the ubiquitous local-density approximation in the context of ensembles.
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The resulting density-functional approximation \trashEF{for ensembles}, based on both finite and infinite uniform electron gas models, automatically incorporates the infamous derivative discontinuity contributions to the excitation energies through its explicit ensemble weight dependence.
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Gross--Oliveira--Kohn (GOK) DFT (\textit{i.e.}, eDFT for neutral
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excitations), and can be seen as a natural extension of the ubiquitous local-density approximation in the context of ensembles.
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The resulting density-functional approximation, based on both finite and infinite uniform electron gas models, automatically incorporates the infamous derivative discontinuity contributions to the excitation energies through its explicit ensemble weight dependence.
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Its accuracy is illustrated by computing single and double excitations in one-dimensional many-electron systems in the weak, intermediate and strong correlation regimes.
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Although the present weight-dependent functional has been specifically
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designed for one-dimensional systems, the methodology proposed here is
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\manu{general}, \ie, directly applicable to the construction of weight-dependent functionals for realistic three-dimensional systems, such as molecules and solids.
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general, \ie, directly applicable to the construction of weight-dependent functionals for realistic three-dimensional systems, such as molecules and solids.
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\end{abstract}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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@ -819,7 +819,7 @@ Note that, within the approximation of Eq.~\eqref{eq:min_with_HF_ener_fun}, the
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optimized with a non-local exchange potential rather than a
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density-functional local one, as expected from
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Eq.~\eqref{eq:var_ener_gokdft}. This procedure is actually general, \ie,
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applicable to not-necessarily spin polarized and real (higher-dimensional) systems.
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applicable to not-necessarily spin-polarized and real (higher-dimensional) systems.
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As readily seen from Eq.~\eqref{eq:eHF-dens_mat_func}, inserting the
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ensemble density matrix into the HF interaction energy functional
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introduces unphysical \textit{ghost-interaction} errors \cite{Gidopoulos_2002, Pastorczak_2014, Alam_2016, Alam_2017, Gould_2017}
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@ -834,9 +834,8 @@ as well as \textit{curvature}:\cite{Alam_2016,Alam_2017}
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\eeq
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The ensemble energy is of course expected to vary linearly with the ensemble
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weights [see Eq.~\eqref{eq:exact_GOK_ens_ener}].
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\manu{
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The explicit linear weight dependence of the ensemble Hx energy is actually restored when evaluating the individual energy
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levels on the basis of Eq.~\eqref{eq:exact_ind_ener_rdm}.}
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levels on the basis of Eq.~\eqref{eq:exact_ind_ener_rdm}.
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Turning to the density-functional ensemble correlation energy, the
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following ensemble local-density approximation (eLDA) will be employed
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@ -1031,9 +1030,9 @@ gaps, can be seen as more relevant in this context. \cite{Loos_2014a, Loos_2014b
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However, an obvious drawback of using finite uniform electron gases is
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that the resulting density-functional approximation for ensembles
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will inexorably depend on the number of electrons in the finite uniform electron gas (see below).
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Here, we propose to construct a weight-dependent eLDA for the
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Here, we propose to construct a weight-dependent LDA functional for the
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calculation of excited states in 1D systems by combining finite uniform electron gases with the
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usual infinite uniform electron gas.
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usual infinite uniform electron gas paradigm.
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As a finite uniform electron gas, we consider the ringium model in which electrons move on a perfect ring (\ie, a circle) but interact \textit{through} the ring. \cite{Loos_2012, Loos_2013a, Loos_2014b}
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The most appealing feature of ringium regarding the development of
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@ -1209,9 +1208,9 @@ We use as basis functions the (orthonormal) orbitals of the one-electron system,
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\end{equation}
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with $ \mu = 1,\ldots,\nBas$ and $\nBas = 30$ for all calculations.
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The convergence threshold $\tau = \max{ \abs{ \bF{\bw} \bGam{\bw}
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\bS - \bS \bGam{\bw} \bF{\bw}}}$ [see Eq.~\eqref{eq:commut_F_AO}] is set
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to $10^{-5}$. For comparison, regular HF and KS-DFT calculations
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are performed with the same threshold.
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\bS - \bS \bGam{\bw} \bF{\bw}}}$ [see Eq.~\eqref{eq:commut_F_AO}] of the KS-DFT self-consistent calculation is set
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to $10^{-5}$.
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%For comparison, regular HF and KS-DFT calculations are performed with the same threshold.
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In order to compute the various density-functional
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integrals that cannot be performed in closed form,
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a 51-point Gauss-Legendre quadrature is employed.
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