done with intro for now
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%% This BibTeX bibliography file was created using BibDesk.
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%% Created for Pierre-Francois Loos at 2020-08-17 09:17:11 +0200
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%% Created for Pierre-Francois Loos at 2020-08-17 10:19:43 +0200
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%% Saved with string encoding Unicode (UTF-8)
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@article{Scemama_2016,
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Author = {Scemama, Anthony and Applencourt, Thomas and Giner, Emmanuel and Caffarel, Michel},
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Date-Added = {2020-08-17 10:18:21 +0200},
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Date-Modified = {2020-08-17 10:18:21 +0200},
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Doi = {10.1002/jcc.24382},
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Issn = {0192-8651},
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Journal = {J. Comput. Chem.},
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Month = {Jun},
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Number = {20},
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Pages = {1866--1875},
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Publisher = {Wiley-Blackwell},
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Title = {Quantum Monte Carlo with very large multideterminant wavefunctions},
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Url = {http://dx.doi.org/10.1002/jcc.24382},
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Volume = {37},
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Year = {2016},
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Bdsk-Url-1 = {http://dx.doi.org/10.1002/jcc.24382}}
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@article{Scemama_2014,
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Author = {Scemama, A. and Applencourt, T. and Giner, E. and Caffarel, M.},
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Date-Added = {2020-08-17 10:18:00 +0200},
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Date-Modified = {2020-08-17 10:18:00 +0200},
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Doi = {10.1063/1.4903985},
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Issn = {1089-7690},
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Journal = {J. Chem. Phys.},
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Month = {Dec},
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Number = {24},
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Pages = {244110},
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Publisher = {AIP Publishing},
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Title = {Accurate nonrelativistic ground-state energies of 3d transition metal atoms},
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Url = {http://dx.doi.org/10.1063/1.4903985},
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Volume = {141},
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Year = {2014},
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Bdsk-Url-1 = {http://dx.doi.org/10.1063/1.4903985}}
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@article{Scemama_2019,
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Author = {A. Scemama and M. Caffarel and A. Benali and D. Jacquemin and P. F. Loos.},
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Date-Added = {2020-08-17 09:16:18 +0200},
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@ -174,13 +174,16 @@ In such cases or when very high accuracy is required, a viable alternative is to
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``post-FCI'' method. A multi-determinant trial wave function is then produced by
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approaching FCI with a SCI method such as the \emph{configuration interaction using a perturbative
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selection made iteratively} (CIPSI) method.\cite{Giner_2013,Giner_2015,Caffarel_2016_2}
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\titou{When the basis set is enlarged, the trial wave function gets closer to
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When the basis set is enlarged, the trial wave function gets closer to
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the exact wave function, so we expect the nodal surface to be
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improved.\cite{Caffarel_2016}}
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This technique has the advantage of using the FCI nodes in a given basis
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set, which is perfectly well defined and therefore makes the calculations reproducible in a
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improved.\cite{Caffarel_2016}
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Note that, as discussed in Ref.~\onlinecite{Caffarel_2016_2}, there is no mathematical guarantee that increasing the size of the one-electron basis lowers the FN-DMC energy, because the variational principle does not explicitly optimize the nodal surface, nor the FN-DMC energy.
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However, in all applications performed so far, \cite{Giner_2013,Scemama_2014,Scemama_2016,Giner_2015,Caffarel_2016,Scemama_2018,Scemama_2018b,Scemama_2019} a systematic decrease of the FN-DMC energy has been observed whenever the SCI trial wave function is improved variationally upon enlargement of the basis set.
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The technique relying on SCI multi-determinant trial wave function described above has the advantage of using near-FCI quality nodes in a given basis
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set, which is perfectly well defined and therefore makes the calculations systematically improvable and reproducible in a
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black-box way without needing any QMC expertise.
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Nevertheless, this technique cannot be applied to large systems because of the
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Nevertheless, this procedure cannot be applied to large systems because of the
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exponential growth of the number of Slater determinants in the trial wave function.
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Extrapolation techniques have been used to estimate the FN-DMC energies
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obtained with FCI wave functions,\cite{Scemama_2018,Scemama_2018b,Scemama_2019} and other authors
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@ -190,13 +193,13 @@ of a Jastrow factor to keep the number of determinants
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small,\cite{Giner_2016} and where the consistency between the
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different wave functions is kept by imposing a constant energy
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difference between the estimated FCI energy and the variational energy
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of the CI wave function.\cite{Dash_2018,Dash_2019}
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of the SCI wave function.\cite{Dash_2018,Dash_2019}
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Nevertheless, finding a robust protocol to obtain high accuracy
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calculations which can be reproduced systematically and
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applicable to large systems with a multi-configurational character is
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still an active field of research. The present paper falls
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within this context.
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The central idea of the present work, and the launch-pad for the remainder of this study, is that one can combine the various strengths of WFT, DFT, and DMC in order to create a new hybrid method with more attractive properties.
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In particular, we show here that one can combine CIPSI and KS-DFT via the range separation (RS) of the interelectronic Coulomb operator \cite{Sav-INC-96a,Toulouse_2004} to obtain accurate FN-DMC energies with compact multi-determinant trial wave functions.
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