diff --git a/Manuscript/FarDFT.tex b/Manuscript/FarDFT.tex index 2dd3f8d..ac54043 100644 --- a/Manuscript/FarDFT.tex +++ b/Manuscript/FarDFT.tex @@ -342,11 +342,21 @@ equals the exact ensemble one n^{\bw}(\br)=\sum_{I=0}^{\nEns-1} \ew{I}n_{\Psi_I}(\br). \eeq - The minimizing density-functional KS -wavefunctions $\left\{\Det{I}{\bw}\left[n^{\bw}\right]\right\}_{0\leq -I\leq M-1}$ are constructed from (weight-dependent) KS orbitals +In practice, the minimizing KS density matrix operator +$\hgam{\bw}\left[\n{}{\bw}\right]$ +can be determined from the following KS reformulation of the +GOK variational principle, \cite{Gross_1988b,Senjean_2015} +\beq\label{eq:min_KS_DM} +\E{}{\bw} = \min_{\hGam{\bw}} \left\{\Tr[\hGam{\bw} +\left(\hT+\hVne\right)]+\E{\Ha}{}[\n{\hGam{\bw}}{}]+\E{\xc}{\bw}[\n{\hGam{\bw}}{}]\right\}, +\eeq +where $\n{\hGam{\bw}}{}(\br)=\sum_{I=0}^{\nEns - 1} +\ew{I}\n{\overline{\Psi}^{(I)}}{}$ is the trial ensemble density. As a +result, the orbitals $\lbrace \MO{p}{\bw}(\br{}) \rbrace_{1 \le p \le -\nOrb}$. The latters are determined by solving the ensemble KS equation +\nOrb}$ from which the KS +wavefunctions $\left\{\Det{I}{\bw}\left[n^{\bw}\right]\right\}_{0\leq +I\leq M-1}$ are constructed can be obtained by solving the following ensemble KS equation \begin{equation} \label{eq:eKS} \qty{ \hHc(\br{}) + \fdv{\E{\Hxc}{\bw}[\n{}{\bw}]}{\n{}{}(\br{})}} \MO{p}{\bw}(\br{}) = \eps{p}{\bw} \MO{p}{\bw}(\br{}), @@ -491,8 +501,19 @@ This study deals only with spin-unpolarised systems, \ie, $\n{\uparrow}{} = \n{\ Moreover, we restrict our study to the case of a two-state ensemble (\ie, $\nEns = 2$) where both the ground state ($I=0$ with weight $1 - \ew{}$) and the first doubly-excited state ($I=1$ with weight $\ew{}$) are considered. Although one should have $0 \le \ew{} \le 1/2$ to ensure the GOK variational principle, we will sometimes ``violate'' this variational constraint. Indeed, the limit $\ew{} = 1$ is of particular interest as it corresponds to a genuine saddle point of the KS equations, and match perfectly the results obtained with the maximum overlap method (MOM) developed by Gilbert, Gill and coworkers. \cite{Gilbert_2008,Barca_2018a,Barca_2018b} -\manu{Maybe we should be more clear about what we mean with $\ew{} = 1$. -In the range $1/2\leq \ew{}\leq 1$, } +\manu{I think we need to be a bit more clear about the $\ew{} = 1$ case, as +it stands a little bit beyond the theory discussed previously. What you +are looking at in the range $1/2\leq \ew{}\leq 1$ are, indeed, other +stationary points (than the minimizing ones) of the density matrix +operator functional in Eq.~(\ref{eq:min_KS_DM}). I would say that we +look at these solutions for analysis purposes. I personally never looked +(formally) at these solutions and their physical meaning. One should clearly +mention that applying GOK-DFT in this range of weights would simply +consists in switching ground and first excited states if a true +minimization of the ensemble energy were performed. From this point of +view we do not violate anything. +} + %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \section{Results} \label{sec:res}