diff --git a/Manuscript/SRGGW.tex b/Manuscript/SRGGW.tex index 50011b4..93ebcf8 100644 --- a/Manuscript/SRGGW.tex +++ b/Manuscript/SRGGW.tex @@ -668,8 +668,8 @@ In practice, one may achieve convergence, in some cases, by adjusting these para However, in order to perform black-box comparisons, these parameters have been fixed to these default values. The $\eta$ value has been set to \num{e-3} for the conventional $G_0W_0$ calculations while, for the (SRG-)qs$GW$ calculations, $\eta$ has been chosen as the largest value where one successfully converges the 50 systems composing the test set. -These many-body perturbation theory values are compared with a CCSD(T) reference. -The CCSD(T) principal ionization potentials (IPs) and electron affinities (EAs) have been obtained using Gaussian 16 \cite{g16} with default parameters, that is, within the restricted and unrestriced HF formalism for the neutral and charged species, respectively. +These many-body perturbation theory values are compared with a $\Delta$CCSD(T) reference. +The $\Delta$CCSD(T) principal ionization potentials (IPs) and electron affinities (EAs) have been obtained using Gaussian 16 \cite{g16} with default parameters, that is, within the restricted and unrestriced HF formalism for the neutral and charged species, respectively. %=================================================================% \section{Results} @@ -696,8 +696,8 @@ Then, the accuracy of the principal IPs and EAs produced by the qs$GW$ and SRG-q \begin{figure*} \includegraphics[width=\linewidth]{fig4.pdf} \caption{ - Error [with respect to $\Delta$CCSD(T)] in the principal IP of \ce{Li2}, \ce{LiH} and \ce{BeO} in the aug-cc-pVTZ basis set as a function of the flow parameter $s$ for the SRG-qs$GW$ method with and without TDA. - The HF and qs$GW$ (with and without TDA) values are reported as dashed lines. + Error [with respect to $\Delta$CCSD(T)] in the principal IP of \ce{Li2}, \ce{LiH} and \ce{BeO} in the aug-cc-pVTZ basis set as a function of the flow parameter $s$ for the SRG-qs$GW$ method. + The HF and qs$GW$ values are reported as dashed lines. \label{fig:fig4}} \end{figure*} %%% %%% %%% %%% @@ -708,7 +708,7 @@ Then, the accuracy of the principal IPs and EAs produced by the qs$GW$ and SRG-q %%%%%%%%%%%%%%%%%%%%%% This section starts by considering a prototypical molecular system, the water molecule, in the aug-cc-pVTZ basis set. -Figure \ref{fig:fig3} shows the error of various methods for the principal IP with respect to the CCSD(T) reference value. +Figure \ref{fig:fig3} shows the error of various methods for the principal IP with respect to the $\Delta$CCSD(T) reference value. The IP at the HF level (dashed black line) is too large; this is a consequence of the missing correlation and the lack of orbital relaxation for the cation, a result that is well understood. \cite{SzaboBook,Lewis_2019} The usual qs$GW$ scheme (dashed blue line) brings a quantitative improvement as the IP is now within \SI{0.3}{\eV} of the reference value. @@ -738,19 +738,20 @@ As soon as $s$ is large enough to decouple the 2h1p block, the IP starts decreas %The TDA values are now underestimating the IP, unlike their RPA counterparts. %For both static self-energies, the TDA leads to a slight increase in the absolute error. -Next, we investigate the flow parameter dependence of SRG-qs$GW$ for three more challenging molecular systems. +Next, the flow parameter dependence of SRG-qs$GW$ is investigated for three more challenging molecular systems. The left panel of Fig.~\ref{fig:fig4} shows the results for the lithium dimer, \ce{Li2}, which is an interesting case because, unlike in water, the HF approximation underestimates the reference IP. -On the other hand, the qs$GW$ and SRG-qs$GW$ IPs are too large. +Yet, the qs$GW$ and SRG-qs$GW$ IPs are still overestimated as in the water molecule case. Indeed, we can see that the positive increase of the SRG-qs$GW$ IP is proportionally more important than for water. In addition, the plateau is reached for larger values of $s$ in comparison to Fig.~\ref{fig:fig3}. %Both TDA results are worse than their RPA versions but, in this case, SRG-qs$GW^\TDA$ is more accurate than qs$GW^\TDA$. -We now turn to lithium hydride, \ce{LiH} (see middle panel of Fig.~\ref{fig:fig4}). +Now turning to lithium hydride, \ce{LiH} (see middle panel of Fig.~\ref{fig:fig4}). In this case, the qs$GW$ IP is actually worse than the fairly accurate HF value. -However, SRG-qs$GW$ improves slightly the accuracy as compared to HF. +However, SRG-qs$GW$ does not suffer from the same problem and improves slightly the accuracy as compared to HF. Finally, beryllium oxide, \ce{BeO}, is considered as it is a well-known example where it is particularly difficult to converge self-consistent $GW$ calculations due to the presence of intruder states. \cite{vanSetten_2015,Veril_2018,Forster_2021} The SRG-qs$GW$ calculations could be converged without any issue even for large $s$ values. +The convergence properties of both schemes will be systematically investigated in the next subsection. Once again, a plateau is attained and the corresponding value is slightly more accurate than its qs$GW$ counterpart. %Note that, for \ce{LiH} and \ce{BeO}, the TDA actually improves the accuracy compared to the RPA-based qs$GW$ schemes. @@ -880,6 +881,7 @@ This means that some intruder states were included in the static correction for However, this is not a problem as the MAE of the test set is already well converged at $s=\num{e3}$. This is illustrated by the blue curve of Fig.~\ref{fig:fig6} which shows the evolution of the MAE with respect to $s$ and $\eta=1/2s^2$. The convergence plateau of the MAE is reached around $s=50$ while the convergence problem arise for $s>\num{e3}$. +Therefore, for future studies using the SRG-qs$GW$ method, a default value of the flow parameter equal to $\num{5e2}$ or $\num{e3}$ seems reasonable. On the other hand, the qs$GW$ convergence behaviour seems to be more erratic. At $\eta=\num{e-2}$ ($s=\num{5e3}$), convergence could not be achieved for 13 molecules while 2 molecules were already problematic at $\eta=\num{5e-2}$ ($s=200$). @@ -909,8 +911,8 @@ The two partially self-consistent methods reduce as well the minimum value but i Note that a positive EA means that the anion state is bound and therefore the methods considered here are well-suited to describe these EAs. On the other hand, a negative EA means that this is a resonance state. -The methods considered in this study, even the CCSD(T) reference, are not able to describe the physics of resonance states, therefore one should not try to give a physical interpretation to these values. -Yet, one can still compare the $GW$ values with their CCSD(T) counterparts within a given basis set in these cases. +The methods considered in this study, even the $\Delta$CCSD(T) reference, are not able to describe the physics of resonance states, therefore one should not try to give a physical interpretation to these values. +Yet, one can still compare the $GW$ values with their $\Delta$CCSD(T) counterparts within a given basis set in these cases. %=================================================================% \section{Conclusion} diff --git a/Manuscript/fig4.pdf b/Manuscript/fig4.pdf index 09bca60..72c7bc8 100644 Binary files a/Manuscript/fig4.pdf and b/Manuscript/fig4.pdf differ