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Pierre-Francois Loos 2021-01-19 12:20:28 +01:00
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Manuscript/sfBSE.tex
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@ -713,10 +713,12 @@ A similar graph comparing (SF-)dBSE and EOM-CCSD excitation energies can be foun
\includegraphics[width=0.4\linewidth]{H2_CIS}
\hspace{0.05\linewidth}
\includegraphics[width=0.4\linewidth]{H2_CIS_S2}
\vspace{0.025\linewidth}
\\
\includegraphics[width=0.4\linewidth]{H2_BHHLYP}
\hspace{0.05\linewidth}
\includegraphics[width=0.4\linewidth]{H2_BHHLYP_S2}
\vspace{0.025\linewidth}
\\
\includegraphics[width=0.4\linewidth]{H2_BSE}
\hspace{0.05\linewidth}
@ -842,7 +844,12 @@ Then, CBD stands as an excellent example for which dynamical corrections are nec
\section{Conclusion}
\label{sec:ccl}
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\alert{Here comes the conclusion.}
In this article, we have presented the extension of the BSE approach of many-body perturbation theory to the spin-flip formalism in order to access double excitations in realistic molecular systems.
The present spin-flip calculations rely on a spin-unrestricted version of the $GW$ approximation and the BSE formalism with, on top of this, a dynamical correction to the static BSE optical excitations via an unrestricted generalization of our recently developed renormalized perturbative treatment.
Taking the beryllium atom, the dissociation of the hydrogen molecule, and cyclobutadiene in two different geometries as examples, we have shown that the spin-flip BSE formalism can accurately model double excitations and seems to surpass systematically its spin-flip TD-DFT parent.
Further improvements could be obtained thanks to a better choice of the starting orbitals and their energies and we hope to investigate this in a forthcoming paper.
Techniques to alleviate the spin contamination in spin-flip calculations will also be explored in the near future.
We hope to these new encouraging results will stimulate new developments around the BSE formalism to further establish it as a valuable \text{ab inito} alternative to TD-DFT for the study of molecular excited states.
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\acknowledgements{