extra part on future stuff

Manuscript/ExPerspective.bib

@@ -1,7 +1,7 @@
 %% This BibTeX bibliography file was created using BibDesk.
 %% http://bibdesk.sourceforge.net/
 
-%% Created for Pierre-Francois Loos at 2019-11-06 20:54:53 +0100 
+%% Created for Pierre-Francois Loos at 2019-11-12 21:17:15 +0100 
 
 
 %% Saved with string encoding Unicode (UTF-8) 
@@ -82,6 +82,13 @@
 @string{theo = {J. Mol. Struct. (THEOCHEM)}}
 
 
+@article{Loo20b,
+	Author = {P. F. Loos and D. Jacquemin},
+	Date-Added = {2019-11-12 21:15:13 +0100},
+	Date-Modified = {2019-11-12 21:16:55 +0100},
+	Title = {Reference Excitation Energies For Radicals And Exotic Molecules},
+	Volume = {in preparation}}
+
 @inbook{Mai12,
 	Address = {Berlin, Heidelberg},
 	Author = {Maitra, Neepa T.},

Manuscript/ExPerspective.tex

@@ -53,6 +53,12 @@
 \newcommand{\InAA}[1]{#1 \AA}
 \newcommand{\kcal}{kcal/mol}
 
+% sets
+\newcommand{\SetA}{QUEST\#1}
+\newcommand{\SetB}{QUEST\#2}
+\newcommand{\SetC}{QUEST\#3}
+
+
 \newcommand{\LCPQ}{Laboratoire de Chimie et Physique Quantiques, Universit\'e de Toulouse, CNRS, UPS, France}
 \newcommand{\CEISAM}{Laboratoire CEISAM - UMR CNRS 6230, Universit\'e de Nantes, 2 Rue de la Houssini\`ere, BP 92208, 44322 Nantes Cedex 3, France}
 
@@ -287,11 +293,12 @@ These two studies clearly demonstrate and motivate the need for higher accuracy
 Recently, we made, what we think, is a significant contribution to this quest for highly accurate excitation energies. \cite{Loo18a}
 More specifically, we studied 18 small molecules with sizes ranging from one to three non-hydrogen atoms.
 For such systems, using a combination of high-order CC methods, SCI calculations and large diffuse basis sets, we were able to compute a list of 110 highly accurate vertical excitation energies for excited states of various natures (valence, Rydberg, $n \ra \pi^*$, $\pi \ra \pi^*$, singlet, triplet and doubly excited) based on accurate CC3/aug-cc-pVTZ geometries.
+In the following, we label this set a {\SetA}.
 Importantly, it allowed us to benchmark a series of 12 popular excited-state wave function methods accounting for double and triple excitations (see Fig.~\ref{fig:Set1}): CIS(D), ADC(2), CC2, STEOM-CCSD, \cite{Noo97} CCSD, CCSDR(3), \cite{Chr77} and CCSDT-3. \cite{Wat96} 
 Our main conclusion was that, although less accurate than CC3, CCSDT-3 can be used as a reliable reference for benchmark studies, and that ADC(3) delivers quite large errors for this set of small compounds, with a clear tendency to overcorrect its second-order version ADC(2).
 
 In a second study, \cite{Loo19c} using a similar combination of theoretical models (but mostly extrapolated SCI energies), we provided accurate reference excitation energies for transitions involving a substantial amount of double excitations using a series of increasingly large diffuse-containing atomic basis sets (up to aug-cc-pVQZ when technically feasible). 
-Our set gathers 20 vertical transitions from 14 small- and medium-sized molecules (acrolein, benzene, beryllium atom, butadiene, carbon dimer and trimer, ethylene, formaldehyde, glyoxal, hexatriene, nitrosomethane, nitroxyl, pyrazine, and tetrazine). 
+Our set gathers 20 vertical transitions from 14 small- and medium-sized molecules (acrolein, benzene, beryllium atom, butadiene, carbon dimer and trimer, ethylene, formaldehyde, glyoxal, hexatriene, nitrosomethane, nitroxyl, pyrazine, and tetrazine), a set we label as {\SetB} in the remaining of this paper.
 An important addition to this second study was the computation of double excitations with multiconfigurational methods (CASSCF, CASPT2, and NEVPT2) in addition to high-order CC methods including perturbative or iterative triple corrections (see Fig.~\ref{fig:Set2}).
 Our results clearly evidence that the error in CC methods is intimately related to the amount of double-excitation character in the vertical transition. 
 For ``pure'' double excitations (\ie, for transitions which do not mix with single excitations), the error in CC3 and CCSDT can easily reach $1$ and $0.5$ eV, respectively, while it goes down to a few tenths of an electronvolt for more common transitions (such as in trans-butadiene) involving a significant amount of singles.
@@ -299,11 +306,21 @@ The quality of the excitation energies obtained with multiconfigurational method
 Interestingly, CASPT2 and NEVPT2 were found to be more accurate for transition with a small percentage of single excitations (error usually below $0.1$ eV) than for excitations dominated by single excitations where the error is more around $0.1$-$0.2$ eV (see Fig.~\ref{fig:Set2}).
 
 In our latest study, \cite{Loo20} in order to provide more general conclusions, we generated highly accurate vertical transition energies for larger compounds with a set composed by 27 molecules encompassing from 4 to 6 non-hydrogen atoms for a total of \alert{238} vertical transition energies of various natures.
+This set, labeled as {\SetC} and still based on CC3/aug-cc-pVTZ geometries, is constituted by a reasonably good balance of singlet, triplet, valence, and Rydberg states.
 To obtain these energies, we employed CC methods up to the highest possible order (CC3, CCSDT, and CCSDTQ), very large SCI calculations (with tens of millions of determinants), as well as the most robust multiconfigurational method, NEVPT2. 
 Each approach was applied in combination with diffuse-containing atomic basis sets.
-For all these transitions, we reported at least CC3/aug-cc-pVQZ transition energies as well as CC3/aug-cc-pVTZ oscillator strengths for each dipole-allowed transition. 
-In agreement with our two previous studies, \cite{Loo18a,Loo19c} we confirmed that CC3 almost systematically delivers transition energies in agreement with higher-level theoretical models ($\pm 0.04$ eV) except for transitions presenting a dominant double excitation character (see Fig.~\ref{fig:Set3}).
+Because the SCI energy converges obviously slower for these larger systems, the extrapolated SCI values were employed as a``safely net'' to demonstrate the overall consistency of our CC-based protocol rather than straight out-of-the-box reference values.
+For all the transitions of the {\SetC} set, we reported at least CC3/aug-cc-pVQZ transition energies as well as CC3/aug-cc-pVTZ oscillator strengths for each dipole-allowed transition. 
+Pursuing our previous benchmarking efforts, \cite{Loo18a,Loo19c} we confirmed that CC3 almost systematically delivers transition energies in agreement with higher-level theoretical models ($\pm 0.04$ eV) except for transitions presenting a dominant double excitation character (see Fig.~\ref{fig:Set3}).
+These findings were in perfect agreement with our two previous studies. \cite{Loo18a,Loo19c}
 This definitely settles down the debate by demonstrating the superiority of CC3 (in terms of accuracy) compared to methods like CCSDT-3 or ADC(3).
+Moreover, thanks to the exhaustive and detailed comparisons made in Ref.~\onlinecite{Loo20}, we could safely conclude that CC3 also regularly outperforms CASPT2 and NEVPT2 as long as the corresponding transition does not show any strong multiple excitation character.
+
+Our current efforts are focussing on expanding and combining these sets to create an \textit{ultimate} test set of highly-accurate excitations energies.
+In particular, we are currently generating reference excitations energies for radicals as well as more ``exotic'' molecules containing heavier atoms (such as \ce{Cl}, \ce{F}, \ce{P}, and \ce{Si}). \cite{Loo20b}
+The combination of these various sets would potentially create a single mega set of more than 400 vertical transition energies for small- and medium-size molecules based on accurate ground-state geometries.
+Such a set would definitely be a terrific asset for the entire electronic structure community. 
+It would surely stimulate further theoretical developments in excited-state methods and provide a fair ground for the assessements of the currently available or under development excited-state models.
 
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