diff --git a/Manuscript/eDFT.tex b/Manuscript/eDFT.tex index c235e60..b82a080 100644 --- a/Manuscript/eDFT.tex +++ b/Manuscript/eDFT.tex @@ -180,7 +180,7 @@ KS scheme, a HF-like Hartree-exchange energy is employed. This formulation is in principle exact and applicable to higher dimensions. Let us start from the analog for ensembles of Levy's universal functional, -\beq +\beq\label{eq:ens_LL_func} F^{\bw}[n]&=& \underset{\hat{\gamma}^{{\bw}}\rightarrow n}{\rm min}\left\{{\rm Tr}\left[\hat{\gamma}^{{\bw}}\left(\hat{T}+\hat{W}_{\rm @@ -188,17 +188,19 @@ ee}\right)\right]\right\} \eeq where ${\rm Tr}$ denotes the trace. The minimization over trial ensemble density matrix operators -$\hat{\gamma}^{{\bw}}=\sum^M_{K=0}w^{(K)}\vert\Psi^{(K)}\rangle\langle\Psi^{(K)}\vert$ +$\hat{\gamma}^{{\bw}}=\sum_{K\geq0}w^{(K)}\vert\Psi^{(K)}\rangle\langle\Psi^{(K)}\vert$ is performed under the following density constraint: \beq {\rm -Tr}\left[\hat{\gamma}^{{\bw}}\hat{n}(\br)\right]=\sum^M_{K=0}w^{(K)}n_{\Psi^{(K)}}(\br)=n(\br), +Tr}\left[\hat{\gamma}^{{\bw}}\hat{n}(\br)\right]=\sum_{K\geq0}w^{(K)}n_{\Psi^{(K)}}(\br)=n(\br), \eeq where $\hat{n}(\br)$ is the density operator, $n_{\Psi}$ denotes the density of wavefunction $\Psi$, and $\bw\equiv\left(w^{(1)},w^{(2)},\ldots\right)$ is the collection of (decreasing) ensemble weights assigned to the excited states. Note that -$w^{(0)}=1-\sum^M_{K>0}w^{(K)}\geq 0$. +$w^{(0)}=1-\sum_{K>0}w^{(K)}\geq 0$.\\ + +Ground-state theory: \beq F^{\bw=0}[n]=F[n]=\underset{\Psi\rightarrow n}{\rm min} @@ -206,7 +208,8 @@ F^{\bw=0}[n]=F[n]=\underset{\Psi\rightarrow n}{\rm min} ee}\ket{\Psi} \eeq -\beq + +\beq\label{eq:generalized_KS-DFT_decomp} F[n]&=& \underset{\Phi\rightarrow n}{\rm min} \bra{\Phi}\hat{T}+\hat{W}_{\rm @@ -228,76 +231,101 @@ W_{\rm HF}\left[{\bmg}\right]\equiv\frac{1}{2} \Tr(\bmg \, \bG \, \bmg) \eeq is the conventional density-matrix functional HF Hartree-exchange -energy. By analogy with Eq.~(\ref{}), - +energy. By analogy with Eq.~(\ref{eq:generalized_KS-DFT_decomp}), we +decompose the ensemble universal functional as follows: \beq -F^{\bw}_{\rm HF}[n]&=& +F^{\bw}[n]&=& \underset{\hat{\Gamma}^{{\bw}}\rightarrow n}{\rm min}\left\{{\rm -Tr}\left[\hat{\Gamma}^{{\bw}}\hat{T}\right]+W_{\rm +Tr}\left[\hat{\Gamma}^{{\bw}}\hat{T}\right] ++W_{\rm HF}\left[{\bmg}^{\bw}\right]\right\} + +\overline{E}^{{\bw}}_{\rm +Hxc}[n] \nonumber\\ -&=&{\rm -Tr}\left[\hat{\Gamma}^{{\bw}}[n]\hat{T}\right]+W_{\rm -HF}\left[{\bmg}^{\bw}[n]\right] +&=& +\underset{{\bmg}^{{\bw}}\rightarrow n}{\rm min} +\left\{ +{\rm Tr} +\left[{\bmg}^{\bw}{\bm t}\right] ++W_{\rm HF}\left[{\bmg}^{\bw}\right] +\right\}+ +\overline{E}^{\bw}_{\rm Hxc}[n] \eeq -where -$\hat{\Gamma}^{{\bw}}=\sum^M_{K=0}w^{(K)}\vert\Phi^{(K)}\rangle\langle\Phi^{(K)}\vert=\sum^M_{K=0}w^{(K)}\hat{\Gamma}^{(K)}$ is an ensemble density matrix operator constructed -from Slater determinants, the ensemble 1RDM elements are $\Gamma_{pq}^{\bw}={\rm -Tr}\left[\hat{\Gamma}^{{\bw}}\hat{a}^\dagger_p\hat{a}_q\right]$, -and $W_{\rm -HF}\left[{\bmg}\right]=\frac{1}{2}\sum_{pqrs}\langle \varphi_p\varphi_q\vert\vert -\varphi_r\varphi_s\rangle -%\times -\Gamma_{pr}\Gamma_{qs}$.\\ - -In-principle-exact decomposition: - +where the minimization in Eq.~(\ref{eq:ens_LL_func}) has been restricted +to density matrix operators \beq -F^{\bw}[n]= F^{\bw}_{\rm HF}[n]+\overline{E}^{{\bw}}_{\rm -Hx}[n]+\overline{E}^{{\bw}}_{\rm c}[n] -\eeq +\hat{\Gamma}^{{\bw}}=\sum_{K\geq 0}w^{(K)}\vert\Phi^{(K)}\rangle\langle\Phi^{(K)}\vert=\sum_{K\geq 0}w^{(K)}\hat{\Gamma}^{(K)} +\eeq +that are constructed from single Slater +determinants $\Phi^{(K)}$. The complementary ensemble Hx energy removes the ghost-interaction errors introduced in $W_{\rm HF}\left[{\bmg}^{\bw}[n]\right]$: \beq \overline{E}^{{\bw}}_{\rm -Hx}[n]=\sum^M_{K=0}w^{(K)}W_{\rm +Hx}[n]&=&\sum_{K\geq0}w^{(K)}W_{\rm HF}\left[{\bmg}^{(K)}[n]\right] -W_{\rm -HF}\left[{\bmg}^{\bw}[n]\right], -\eeq -which gives in the canonical orbital basis -\beq -&&\overline{E}^{{\bw}}_{\rm -Hx}[n]= -\dfrac{1}{2}\sum_{pq} -\langle \varphi^{{\bw}}_p[n]\varphi^{{\bw}}_q[n]\vert\vert -\varphi^{{\bw}}_p[n]\varphi^{{\bw}}_q[n]\rangle +HF}\left[{\bmg}^{\bw}[n]\right]. \nonumber\\ -&&\times\left[\sum^M_{K=0}w^{(K)}\nu^{(K)}_p \left(\nu^{(K)}_q --\sum^M_{L=0}w^{(L)} \nu^{(L)}_q\right)\right] -.\eeq -\manu{I would guess that, in a uniform system, the GOK-DFT and our -canonical orbitals are the same. This is nice since we can construct -in a clean way density-functional approximations for both $\overline{E}^{{\bw}}_{\rm -Hx}[n]$ and $E^{{\bw}}_{\rm c}[n]$ functionals. Am I right ?} +&=& +{\rm +Tr}\left[\hat{\Gamma}^{{\bw}}[n]\hat{W}_{\rm ee}\right]-W_{\rm +HF}\left[{\bmg}^{\bw}[n]\right] +\eeq + +Note that $\overline{E}^{{\bw}=0}_{\rm +Hx}[n]=0$.\\ + +Ensemble correlation energy: -Variational expression for the ensemble energy: \beq -E^{{\bw}}=\underset{\hat{\Gamma}^{{\bw}}}{\rm min}\Big\{ -&&{\rm -Tr}\left[\hat{\Gamma}^{{\bw}}\hat{T}\right]+W_{\rm +\overline{E}^{{\bw}}_{\rm +c}[n]&=& +{\rm +Tr}\left[\hat{\gamma}^{{\bw}}[n]\left(\hat{T}+\hat{W}_{\rm +ee}\right)\right] +\nonumber\\ +&&- +{\rm +Tr}\left[\hat{\Gamma}^{{\bw}}[n]\left(\hat{T}+\hat{W}_{\rm +ee}\right)\right] +\eeq + +Variational expression of the ensemble energy: +\beq +E^{{\bw}}=\underset{{\bmg}^{{\bw}}}{\rm min}\Big\{ +{\rm +Tr}\left[{\bmg}^{{\bw}}{\bm h}\right]+W_{\rm HF}\left[{\bmg}^{\bw}\right] + \overline{E}^{{\bw}}_{\rm -Hxc}\left[n_{\hat{\Gamma}^{{\bw}}}\right] +Hxc}\left[n_{{\bmg}^{{\bw}}}\right] %+E^{{\bw}}_{\rm c}\left[n_{\hat{\Gamma}^{{\bw}}}\right] -\nonumber\\ -&& -+\int d{\br}\;v_{\rm ext}({\bfr})n_{\hat{\Gamma}^{{\bw}}}({\bfr}) \Big\} \eeq + +For $K>0$ + +\alert{ +\beq +\dfrac{\partial E^{{\bw}}}{\partial w^{(K)}}&=&{\rm +Tr}\left[{\bmg}^{(K)}{\bm h}\right]-{\rm +Tr}\left[{\bmg}^{(0)}{\bm h}\right] +\nonumber\\ +&&+\Tr(\bmg^{(K)} \, \bG \, \bmg^{\bw}) +-\Tr(\bmg^{(0)} \, \bG \, \bmg^{\bw}) ++... +\eeq +\beq +E^{(I)}&=&E^{{\bw}}+\sum_{K>0}\left(\delta_{IK}-w^{(K)}\right)\dfrac{\partial E^{{\bw}}}{\partial w^{(K)}} +\nonumber\\ +&=& +...+\dfrac{1}{2}\Tr(\bmg^{\bw} \, \bG \, \bmg^{\bw}) ++... +\eeq +} Note that, if we use orbital rotations, the gradient of the DFT energy contributions can be expressed as follows,