diff --git a/Manuscript/rsdft-cipsi-qmc.tex b/Manuscript/rsdft-cipsi-qmc.tex index dbad796..3b5e3ce 100644 --- a/Manuscript/rsdft-cipsi-qmc.tex +++ b/Manuscript/rsdft-cipsi-qmc.tex @@ -556,7 +556,7 @@ This is a key result of the present study. \label{sec:rsdft-j} %====================================================== The data presented in Sec.~\ref{sec:fndmc_mu} evidence that, in a finite basis, RS-DFT can provide -trial wave functions with better nodes than FCI wave function. +trial wave functions with better nodes than FCI wave functions. As mentioned in Sec.~\ref{sec:SD}, such behavior can be directly compared to the common practice of re-optimizing the multi-determinant part of a trial wave function $\Psi$ (the so-called Slater part) in the presence of the exponentiated Jastrow factor $e^J$. \cite{Umrigar_2005,Scemama_2006,Umrigar_2007,Toulouse_2007,Toulouse_2008} Hence, in the present paragraph, we would like to elaborate further on the link between RS-DFT @@ -564,7 +564,7 @@ and wave function optimization in the presence of a Jastrow factor. For the sake of simplicity, the molecular orbitals and the Jastrow factor are kept fixed; only the CI coefficients are varied. -Let us assume a fixed Jastrow factor $J(\br_1, \ldots , \br_\Nelec)$ (where $\br_i$ is the position of the $i$th electron and $\Nelec$ the total number of electrons), +Let us then assume a fixed Jastrow factor $J(\br_1, \ldots , \br_\Nelec)$ (where $\br_i$ is the position of the $i$th electron and $\Nelec$ the total number of electrons), and a corresponding Slater-Jastrow wave function $\Phi = e^J \Psi$, where \begin{equation} @@ -597,8 +597,8 @@ To do so, we have made the following numerical experiment. First, we extract the 200 determinants with the largest weights in the FCI wave function out of a large CIPSI calculation obtained with the VDZ-BFD basis. Within this set of determinants, we solve the self-consistent equations of RS-DFT [see Eq.~\eqref{rs-dft-eigen-equation}] -for different values of $\mu$ using the srPBE functional. This gives the CI expansions $\Psi^\mu$. -Then, within the same set of determinants we optimize the CI coefficients $c_I$ [see Eq.~\eqref{eq:Slater}] in the presence of +for different values of $\mu$ using the srPBE functional. This gives the CI expansions of $\Psi^\mu$. +Then, within the same set of determinants we optimize the CI coefficients in the presence of a simple one- and two-body Jastrow factor $e^J$ with $J = J_\text{eN} + J_\text{ee}$ and \begin{subequations} \begin{gather} @@ -617,7 +617,7 @@ The parameters $a=1/2$ and $b=0.89$ were fixed, and the parameters $\gamma_{\text{O}}=1.15$ and $\gamma_{\text{H}}=0.35$ were obtained by energy minimization of a single determinant. The optimal CI expansion $\Psi^J$ is obtained by sampling the matrix elements -of the Hamiltonian ($\mathbf{H}$) and the overlap ($\mathbf{S}$), in the +of the Hamiltonian ($\mathbf{H}$) and overlap ($\mathbf{S}$) matrices in the basis of Jastrow-correlated determinants $e^J D_i$: \begin{subequations} \begin{gather} @@ -678,17 +678,16 @@ report several quantities related to the one- and two-body densities of $\Psi^J$ and $\Psi^\mu$ with different values of $\mu$. First, we report in the legend of the right panel of Fig~\ref{fig:densities} the integrated on-top pair density \begin{equation} - \expval{ P } = \int d\br \,\,n_2(\br,\br), + \expval{ P } = \int d\br \,n_2(\br,\br), \end{equation} -where $n_2(\br_1,\br_2)$ is the two-body density [normalized to $\Nelec(\Nelec-1)$] -obtained for both $\Psi^\mu$ and $\Psi^J$. -Then, in order to have a pictorial representation of both the on-top -pair density and the density, we report in Fig.~\ref{fig:densities} -the plots of the total density $n(\br)$ and on-top pair density -$n_2(\br,\br)$ along one of the \ce{O-H} axis of the water molecule. +obtained for both $\Psi^\mu$ and $\Psi^J$, +where $n_2(\br_1,\br_2)$ is the two-body density [normalized to $\Nelec(\Nelec-1)$]. +Then, in order to have a pictorial representation of both the one-body density $n(\br)$ and the on-top +pair density $n_2(\br,\br)$, we report in Fig.~\ref{fig:densities} +the plots of $n(\br)$ and $n_2(\br,\br)$ along one of the \ce{O-H} axis of the water molecule. From these data, one can clearly notice several trends. -First, the overall on-top pair density decreases when $\mu$ increases, +First, the integrated on-top pair density $\expval{ P }$ decreases when $\mu$ increases, which is expected as the two-electron interaction increases in $H^\mu[n]$. Second, Fig.~\ref{fig:densities} shows that the relative variations of the on-top pair density with respect to $\mu$ @@ -709,10 +708,10 @@ and therefore that the operators that produced these wave functions (\ie, $H^\mu Considering the form of $\hat{H}^\mu[n]$ [see Eq.~\eqref{H_mu}], one can notice that the differences with respect to the usual bare Hamiltonian come from the non-divergent two-body interaction $\hat{W}_{\text{ee}}^{\text{lr},\mu}$ -and the effective one-body potential $\hat{\bar{V}}_{\text{Hxc}}^{\text{sr},\mu}[n]$ which is the functional derivative of the Hartree-exchange-correlation functional. +and the effective one-body potential $\hat{\bar{V}}_{\text{Hxc}}^{\text{sr},\mu}[n]$ which is the functional derivative of the Hxc functional. The roles of these two terms are therefore very different: with respect to the exact ground-state wave function $\Psi$, the non-divergent two-body interaction -increases the probability to find electrons at short distances in $\Psi^\mu$, +increases the probability of finding electrons at short distances in $\Psi^\mu$, while the effective one-body potential $\hat{\bar{V}}_{\text{Hxc}}^{\text{sr},\mu}[n_{\Psi^{\mu}}]$, providing that it is exact, maintains the exact one-body density. This is clearly what has been observed in @@ -723,7 +722,7 @@ can be non-divergent when a proper two-body Jastrow factor $J_\text{ee}$ is chos There is therefore a clear parallel between $\hat{W}_{\text{ee}}^{\text{lr},\mu}$ in RS-DFT and $J_\text{ee}$ in FN-DMC. Moreover, the one-body Jastrow term $J_\text{eN}$ ensures that the one-body density remain unchanged when the CI coefficients are re-optmized in the presence of $J_\text{ee}$. There is then a second clear parallel between $\hat{\bar{V}}_{\text{Hxc}}^{\text{sr},\mu}[n]$ in RS-DFT and $J_\text{eN}$ in FN-DMC. -Thus, one can understand the similarity between the eigenfunctions of $H^\mu$ and the Slater-Jastrow optimization: +Thus, one can understand the similarity between the eigenfunctions of $H^\mu$ and the optimization of the Slater-Jastrow wave function: they both deal with an effective non-divergent interaction but still produce a reasonable one-body density.