first iteration of Sec II done
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@ 121,8 +121,8 @@ Presentday DFT calculations are almost exclusively done within the socalled Ko


transfers the complexity of the manybody problem to the exchangecorrelation (xc) functional thanks to a judicious mapping between a noninteracting reference system and its interacting analog which both have exactly the same oneelectron density.


KSDFT \cite{Hohenberg_1964,Kohn_1965} is now the workhorse of electronic structure calculations for atoms, molecules and solids thanks to its very favorable accuracy/cost ratio. \cite{ParrBook}


As compared to WFT, DFT has the indisputable advantage of converging much faster with respect to the size of the basis set. \cite{FraMusLupTouJCP15,Loos_2019d,Giner_2020}


However, there is no systematic way of refining the approximation of the unknown exact xc functional, and therefore in practice


one faces the unsettling choice of the \emph{approximate} xc functional. \cite{Becke_2014}


\titou{However, there is no systematic way of refining the approximation of the unknown exact xc functional, and therefore in practice


one faces the unsettling choice of the \emph{approximate} xc functional. \cite{Becke_2014}}


Moreover, because of the approximate nature of the xc functional, although the resolution of the KS equations is variational, the resulting KS energy does not have such property.




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@ 280,20 +280,11 @@ to the FCI wave function. At each iteration, the lowest eigenpair is


extracted from the CI matrix expressed in the determinant subspace,


and the FCI energy can be estimated by adding up to the variational energy


a secondorder perturbative correction (PT2), $\EPT$.


The magnitude of $\EPT$ is a


measure of the distance to the FCI energy and a diagnostic of the the quality of the wave function.


\titou{Within the CIPSI algorithm originally developed by Huron \textit{et al.} in Ref.~\onlinecite{Huron_1973} and efficiently implemented as described in Ref.~\onlinecite{Garniron_2019}, the PT2


correction is computed along with the determinant selection. So the


magnitude of $\EPT$ can be made the only parameter of the algorithm,


and we choose this parameter as the convergence criterion of the CIPSI


algorithm.}




\titou{Considering that the perturbatively corrected energy is a reliable


estimate of the FCI energy, using a fixed value of the PT2 correction


as a stopping criterion enforces a constant distance of all the


calculations to the FCI energy. In this work, we target the chemical


accuracy so all the CIPSI selections were made such that $\abs{\EPT} <


1$ m\hartree{}.}


The magnitude of $\EPT$ is a measure of the distance to the FCI energy


and a diagnostic of the the quality of the wave function.


Within the CIPSI algorithm originally developed by Huron \textit{et al.} in Ref.~\onlinecite{Huron_1973} and efficiently implemented as described in Ref.~\onlinecite{Garniron_2019}, the PT2


correction is computed simultaneously to the determinant selection at no extra cost.


$\EPT$ is then the sole parameter of the CIPSI algorithm and is chosen to be its convergence criterion.




%=================================


\subsection{Rangeseparated DFT}


@ 444,7 +435,8 @@ of the localdensity approximation (LDA)\cite{SavINC96a,TouSavFlaIJQC04} and


and correlation functionals defined in


Ref.~\onlinecite{GolWerStoLeiGorSavCP06} (see also


Refs.~\onlinecite{TouColSavJCP05,GolWerStoPCCP05}).


The convergence criterion for stopping the CIPSI calculations


In this work, we target chemical accuracy, so


the convergence criterion for stopping the CIPSI calculations


has been set to $\EPT < 10^{3}$ \hartree{} or $ \Ndet > 10^7$.


All the wave functions are eigenfunctions of the $\Hat{S}^2$ spin operator, as


described in Ref.~\onlinecite{Applencourt_2018}.



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