Added the results for mu = 0.4 and comments in the conclusion.
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@ -2146,6 +2146,19 @@
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Volume = {143},
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Volume = {143},
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Year = {2015},
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Year = {2015},
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Bdsk-Url-1 = {https://doi.org/10.1063/1.4932595}}
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Bdsk-Url-1 = {https://doi.org/10.1063/1.4932595}}
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@article{Toulouse_2004,
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title={Short-range exchange-correlation energy of a uniform electron gas with modified electron--electron interaction},
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author={Toulouse, Julien and Savin, Andreas and Flad, Heinz-J{\"u}rgen},
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journal={Int. J. Quantum Chem.},
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volume={100},
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number={6},
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pages={1047--1056},
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year={2004},
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publisher={Wiley Online Library},
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url={https://doi.org/10.1002/qua.20259}
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}
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@article{Blunt_2017,
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@article{Blunt_2017,
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Author = {Blunt, N. S. and Neuscamman, Eric},
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Author = {Blunt, N. S. and Neuscamman, Eric},
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@ -648,7 +648,12 @@ For $\RHH = 3.7$ bohr, it is much harder to get an accurate estimate of the exci
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As expected from the linearity of the ensemble energy, the GIC-S functional coupled or not with a correlation functional yield extremely stable excitation energies as a function of the weight, with only a few tenths of eV difference between the zero- and equi-weights limits.
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As expected from the linearity of the ensemble energy, the GIC-S functional coupled or not with a correlation functional yield extremely stable excitation energies as a function of the weight, with only a few tenths of eV difference between the zero- and equi-weights limits.
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Nonetheless, the excitation energy is still off by $3$ eV.
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Nonetheless, the excitation energy is still off by $3$ eV.
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The fundamental theoretical reason of such a poor agreement is not clear.
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The fundamental theoretical reason of such a poor agreement is not clear.
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The fact that HF exchange yields better excitation energies hints at the effect of self-interaction error.
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The fact that HF exchange yields better excitation energies hints at the effect of self-interaction error. For additional comparison, we provide the
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excitation energy
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calculated by short-range multiconfigurational DFT in Ref.~\cite{Senjean_2015}, using the (weight-independent) srLDA functional~\cite{Toulouse_2004}
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and setting the range-separation parameter to $\mu = 0.4$ bohr$^{-1}$.
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The excitation energy improves by 1 eV compared
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to the weight-independent S-VWN5 functional, thus showing that treating the long-range part of the electron-electron repulsion by wavefunction theory plays a significant role.
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%\bruno{I'm a bit surprise that the ensemble correction to the correlation functional does not improve things at all... Is the derivative discontinuity, computed with this functional, almost 0 here ?}
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%\bruno{I'm a bit surprise that the ensemble correction to the correlation functional does not improve things at all... Is the derivative discontinuity, computed with this functional, almost 0 here ?}
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%%% TABLE IV %%%
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%%% TABLE IV %%%
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@ -677,11 +682,14 @@ Excitation energies (in eV) associated with the lowest double excitation of \ce{
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B3 & LYP & & & & 5.55 \\
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B3 & LYP & & & & 5.55 \\
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HF & LYP & & & & 6.68 \\
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HF & LYP & & & & 6.68 \\
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\hline
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\hline
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\mc{5}{l}{Accurate\fnm[2]} & 8.69 \\
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\mc{2}{l}{srLDA($\mu = 0.4$) \fnm[2]} & 6,39 & 6,55 & 6,47 & \\
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\hline
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\mc{5}{l}{Accurate\fnm[3]} & 8.69 \\
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\end{tabular}
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\end{tabular}
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\end{ruledtabular}
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\end{ruledtabular}
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\fnt[1]{KS calculation does not converge.}
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\fnt[1]{KS calculation does not converge.}
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\fnt[2]{FCI/aug-cc-pV5Z calculation performed with QUANTUM PACKAGE. \cite{QP2}}
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\fnt[2]{short-range multi-configurational DFT / aug-cc-pVQZ calculations performed in Ref.~\cite{Senjean_2015}}
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\fnt[3]{FCI/aug-cc-pV5Z calculation performed with QUANTUM PACKAGE. \cite{QP2}}
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\end{table}
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\end{table}
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%%% %%% %%% %%%
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%%% %%% %%% %%%
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@ -780,6 +788,14 @@ Excitation energies (in hartree) associated with the lowest double excitation of
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\section{Conclusion}
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\section{Conclusion}
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\label{sec:ccl}
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\label{sec:ccl}
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Although the weight-dependent functionals developed in this paper perform systematically
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better than their
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weight-independent counterparts, the improvement remains small.
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To better understand the reasons of this small improvement,
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it will be particularly interesting to investigate
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the error due to the self-consistent procedure,
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\ie, by checking the difference in the excitation energy when the {\it exact} ensemble density (built with the exact individual densities) is used instead
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of the converged one. Density-driven as well as state-driven errors~\cite{Gould_2019,Fromager_2020} can also be calculated to provide more flavours about the results obtained in this paper. This is left for future work.
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In the light of the results obtained in this study on double excitations computed within the GOK-DFT framework, we believe that the development of more universal weight-dependent exchange and correlation functionals has a bright future, and we hope to be able to report further on this in the near future.
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In the light of the results obtained in this study on double excitations computed within the GOK-DFT framework, we believe that the development of more universal weight-dependent exchange and correlation functionals has a bright future, and we hope to be able to report further on this in the near future.
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%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%
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