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\begin{letter}%
{To the Editors of the Journal of Physical Chemistry Letters}

\opening{Dear Editors,}

\justifying
Please find enclosed our manuscript entitled
\begin{quote}
\textit{``Pros and Cons of the Bethe-Salpeter Formalism for Ground-State Energies''}, 
\end{quote}
which we would like you to consider as a Letter in the \textit{Journal of Physical Chemistry Letters}.
This contribution fits nicely in the section \textit{``Spectroscopy and Photochemistry; General theory''}. 
This contribution has never been submitted in total nor in parts to any other journal, and has been seen and approved by all authors.

In the past few years, the Bethe-Salpeter formalism has demonstrated to be a valuable and cost-effective alternative to TD-DFT to compute excitation energies.
It has gained significant momentum, not only in Physics, but also within the Chemistry community, and is now available in several popular quantum chemistry software packages.
It is now a genuine multidisciplinary methodology that can be applied to materials as well as molecular systems.
Although less popular to date, the Bethe-Salpeter formalism can also be applied to compute ground-state energies via the adiabatic-connection fluctuation dissipation formalism.

The present Letter provides, what we believe, are two important messages.
On the one hand, we show that Bethe-Salpeter can provide extremely accurate total energies and equilibrium bond distances.
We have illustrated this for 8 diatomic molecules for which we have also computed reference ground-state data using increasingly accurate coupled cluster methods.
For the larger systems considered here, we observe that Bethe-Salpeter recovers 99\% of the CC3 correlation energy and yields outstanding equilibrium bond lengths.  
It should be stressed that such a success cannot be not reached with popular quantum chemistry methods such as MP2, CC2 or CCSD, and was never shown before.
On the other hand, we have also observed that, in some cases, unphysical irregularities on the ground-state potential energy surfaces due to the appearance of a satellite resonance with a weight similar to that of the GW quasiparticle peak. 

Because of the large impact of our work, we expect it to be of interest to a wide audience within the chemistry community and beyond.
We suggest Julien Toulouse, Patrick Rinke, Michael van Setten, Timothy Berkelbach, Fabien Bruneval, Wim Klopper, Trygve Helgaker, Pina Romaniello, and Lucia Reining as potential referees.
We look forward to hearing from you soon.

\closing{Sincerely, the authors.}


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