modification in abstract and conclusion
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\begin{abstract}


By combining densityfunctional theory (DFT) and wave function theory (WFT) via the range separation (RS) of the interelectronic Coulomb operator, we obtain accurate fixednode diffusion Monte Carlo (FNDMC) energies with compact multideterminant trial wave functions.


These compact trial wave functions are generated via the diagonalization of the RSDFT Hamiltonian.


In particular, we combine here shortrange correlation functionals with selected configuration interaction (SCI).


As the WFT method is relieved from describing the shortrange part of the correlation hole around the electronelectron coalescence points, the number of determinants in the trial wave function required to reach a given accuracy is significantly reduced as compared to a conventional SCI calculation.


Having low energies does not mean that they are good for chemical properties.


\titou{T2: work in progress.}


In particular, we combine here shortrange exchangecorrelation functionals with a flavor of selected configuration interaction (SCI) known as \emph{configuration interaction using a perturbative selection made iteratively} (CIPSI), a scheme that we label RSDFTCIPSI.


One of the takehome messages of the present study is that RSDFTCIPSI trial wave functions yield lower fixednode energies with more compact multideterminant expansion than CIPSI.


Indeed, as the CIPSI method is relieved from describing the shortrange part of the correlation hole around the electronelectron coalescence points, the number of determinants in the trial wave function required to reach a given accuracy is significantly reduced as compared to a conventional CIPSI calculation.


Importantly, by performing various numerical experiments, we evidence that the RSDFT scheme essentially plays the role of a simple Jastrow factor by mimicking shortrange correlation effects.


Considering the 55 atomization energies of the Gaussian1 benchmark set of molecules, we show that using a fixed value of $\mu=0.5$~bohr$^{1}$ provides an effective cancellation of errors as well as compact trial wave functions, making the present method a good candidate for the accurate description of large systems.


\end{abstract}




\maketitle


@ 547,7 +547,7 @@ Accordingly, all the RSDFT calculations are performed with the srPBE functional




Another important aspect here is the compactness of the trial wave functions $\Psi^\mu$:


at $\mu=1.75$~bohr$^{1}$, $\Psi^{\mu}$ has \textit{only} $54\,540$ determinants at the srPBE/VDZBFD level, while the FCI wave function contains $200\,521$ determinants (see Table \ref{tab:h2odmc}). Even at the srPBE/VTZBFD level, we observe a reduction by a factor two in the number of determinants between the optimal $\mu$ value and $\mu = \infty$.


The takehome message of this first numerical study is that RSDFT trial wave functions can yield a lower fixednode energy with more compact multideterminant expansion as compared to FCI.


The takehome message of this first numerical study is that RSDFTCIPSI trial wave functions can yield a lower fixednode energy with more compact multideterminant expansion as compared to FCI.


This is a key result of the present study.




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


@ 654,7 +654,7 @@ Also, it is interesting to notice that the FNDMC energy of $\Psi^J$ is compatib


with that of $\Psi^\mu$ for $0.5 < \mu < 1$~bohr$^{1}$, as shown by the overlap between the red and blue bands.


This confirms that introducing shortrange correlation with DFT has


an impact on the CI coefficients similar to a Jastrow factor.


This is yet another key result of the present study.


This is another key result of the present study.




%%% FIG 4 %%%


\begin{figure*}


@ 728,6 +728,7 @@ produce a reasonable onebody density.




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


\subsection{Intermediate conclusions}


\label{sec:int_ccl}


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




As conclusions of the first part of this study, we can highlight the following observations:


@ 912,7 +913,7 @@ are even lower than those obtained with the optimal value of


$\mu$. Although the FNDMC energies are higher, the numbers show that


they are more consistent from one system to another, giving improved


cancellations of errors.


This is another key result of the present study, and it can be explained by the lack of sizeconsistency when one considers different $\mu$ values for the molecule and the isolated atoms.


This is yet another key result of the present study, and it can be explained by the lack of sizeconsistency when one considers different $\mu$ values for the molecule and the isolated atoms.


This observation was also mentioned in the context of optimallytune rangeseparated hybrids. \cite{Stein_2009,Karolewski_2013,Kronik_2012}




%%% FIG 6 %%%


@ 965,7 +966,8 @@ on the determinant expansion is similar to the effect of reoptimizing


the CI coefficients in the presence of a Jastrow factor, but without


the burden of performing a stochastic optimization.




Varying the rangeseparation parameter $\mu$ and approaching the


In addition to the intermediate conclusions drawn in Sec.~\ref{sec:int_ccl},


we can affirm that varying the rangeseparation parameter $\mu$ and approaching


RSDFTFCI with CIPSI provides a way to adapt the number of


determinants in the trial wave function, leading always to


sizeconsistent FNDMC energies.


@ 975,7 +977,7 @@ energy via the variation of the parameter $\mu$.


The second method is for the computation of energy differences, where


the target is not the lowest possible FNDMC energies but the best


possible cancellation of errors. Using a fixed value of $\mu$


increases the consistency of the trial wave functions, and we have found


increases the (size)consistency of the trial wave functions, and we have found


that $\mu=0.5$~bohr$^{1}$ is the value where the cancellation of


errors is the most effective.


Moreover, such a small value of $\mu$ gives extremely



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