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eginer 2019-10-17 18:58:37 +02:00
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@ -497,9 +497,8 @@ Such a property is also important in the context of covalent bond breaking where
\subsubsection{Condition for the functional $\efuncdenpbe{\argebasis}$ to obtain $S_z$ invariance}
A sufficient condition to achieve $S_z$ invariance is to eliminate all dependency to $S_z$, which in the case of $\ecmd(\argecmd)$ is the spin polarisation $\zeta(\br{})$ involved in the correlation energy density $\varepsilon_{\text{c,PBE}}(\argepbe)$ (see equation \eqref{eq:def_ecmdpbe}).
Of course, the dependency on the spin polarisation of the functionals can be thought as an aterfact
A possible way to eliminate the $S_z$ dependency would be to simply set $\zeta(\br{})=0$, but this would lower the accuracy of the usual PBE correlation functional $\varepsilon_{\text{c,PBE}}(\argepbe)$.
Therefore, we use the effective spin polarisation introduced by Scuseria and co-workers\cite{GarBulHenScu-PCCP-15} which depends on the on-top pair density and the total density of a general multi configurational wave function $\psibasis$:
As originally shown by Perdew and co-workers\cite{PerSavBur-PRA-95}, the dependence on the spin polarisation in the KS-DFT framework can be removed by the reformulating the spin polarisation of a single Slater determinant with the on-top pair density and the total density. In other terms, the spin density dependence of the correlation functionals usually try to mimic the on-top pair density of a given system.
Based on this reasoning, a similar approach has been used in the context of multi configurational DFT approaches where an effective spin density is introduced
\begin{equation}
\label{eq:def_effspin}
\tilde{\zeta}(n,\ntwo_{\psibasis}) =
@ -508,6 +507,8 @@ Therefore, we use the effective spin polarisation introduced by Scuseria and co-
0 & \text{otherwise.}
\end{cases}
\end{equation}
A possible way to eliminate the $S_z$ dependency would be to simply set $\zeta(\br{})=0$, but this would lower the accuracy of the usual PBE correlation functional $\varepsilon_{\text{c,PBE}}(\argepbe)$.
Therefore, we use the effective spin polarisation introduced by Scuseria and co-workers\cite{GarBulHenScu-PCCP-15} which depends on the on-top pair density and the total density of a general multi configurational wave function $\psibasis$:
If the density $n$ and on-top pair density $\ntwo_{\psibasis}$ are obtained from a single HF determinant, the definition \eqref{eq:def_effspin} is equivalent to the usual one
\begin{equation}
\tilde{\zeta}(n^{\text{HF}},\ntwohf) = n_{\alpha}^{\text{HF}} - n_{\beta}^{\text{HF}},