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Pierre-Francois Loos 2022-03-30 17:30:50 +02:00
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Manuscript/CBD.tex
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@ -428,11 +428,12 @@ Note that, due to error bar inherently linked to the CIPSI calculations (see Sub
\subsection{Geometries} \subsection{Geometries}
\label{sec:geometries} \label{sec:geometries}
Two different sets of geometries obtained with different levels of theory are considered for the ground state property and for the excited states of the CBD molecule. Two different sets of geometries obtained with different levels of theory are considered for the ground state property and for the excited states of the CBD molecule.
First, for the autoisomerization barrier because we consider an energy difference between two geometries it is paramount to obtain these geometries at the same level of theory. First, because the autoisomerization barrier is computed as an energy difference between distinct geometries, it is paramount to obtain these at the same level of theory.
Due to the fact that the square CBD is an open-shell molecule, it is difficult to optimize the geometry so the most accurate method that we can use for both structures is CASPT2(12,12)/aug-cc-pVTZ. However, due to the fact that the ground state of the square arrangement is a transition state of singlet open-shell nature, it is technically difficult to optimize the geometry with high-order CC methods.
Then, for the excited states because we look at vertical energy transitions in one particular geometry we can use different methods for the different structures and use the most accurate method for each geometry. Therefore, we have chosen to rely on CASPT2(12,12)/aug-cc-pVTZ for both the {\Dtwo} and {\Dfour} structures.
So in the case of the excited states of the CBD molecule we use CC3/aug-cc-pVTZ for the rectangular ({\Dtwo}) geometry and we use RO-CCSD(T)/aug-cc-pVTZ for the square ({\Dfour}) geometry. Second, because the vertical transition energies are computed for a particular geometry, we can afford to use different methods for the rectangular and square structures.
Table \ref{tab:geometries} shows the results on the geometry parameters obtained with the different methods. Hence, we rely on CC3/aug-cc-pVTZ for the rectangular ({\Dtwo}) geometry and restricted open-shell version of CCSD(T)/aug-cc-pVTZ for the square ({\Dfour}) geometry.
Table \ref{tab:geometries} reports the key geometrical parameters obtained with these different methods.
%%% TABLE I %%% %%% TABLE I %%%
\begin{squeezetable} \begin{squeezetable}
@ -445,18 +446,19 @@ Table \ref{tab:geometries} shows the results on the geometry parameters obtained
State & Method & \ce{C=C} & \ce{C-C} & \ce{C-H} & \ce{H-C=C}\fnm[1] \\ State & Method & \ce{C=C} & \ce{C-C} & \ce{C-H} & \ce{H-C=C}\fnm[1] \\
\hline \hline
{\Dtwo} ({\oneAg}) & {\Dtwo} ({\oneAg}) &
CASPT2(12,12)/aug-cc-pVTZ & 1.355 & 1.566 & 1.077 & 134.99 \\ CASPT2(12,12)/aug-cc-pVTZ \fnm[2] & 1.355 & 1.566 & 1.077 & 134.99 \\
&CC3/aug-cc-pVTZ & 1.344 & 1.565 & 1.076 & 135.08 \\ &CC3/aug-cc-pVTZ \fnm[2] & 1.344 & 1.565 & 1.076 & 135.08 \\
&CCSD(T)/cc-pVTZ & 1.343 & 1.566 & 1.074 & 135.09 \fnm[2]\\ &CCSD(T)/cc-pVTZ \fnm[3] & 1.343 & 1.566 & 1.074 & 135.09\\
{\Dfour} ({\sBoneg}) & {\Dfour} ({\sBoneg}) &
CASPT2(12,12)/aug-cc-pVTZ & 1.449 & 1.449 & 1.076 & 135.00 \\ CASPT2(12,12)/aug-cc-pVTZ \fnm[2] & 1.449 & 1.449 & 1.076 & 135.00 \\
{\Dfour} ({\Atwog}) & {\Dfour} ({\Atwog}) &
CASPT2(12,12)/aug-cc-pVTZ & 1.445 & 1.445 & 1.076 & 135.00 \\ CASPT2(12,12)/aug-cc-pVTZ \fnm[2] & 1.445 & 1.445 & 1.076 & 135.00 \\
&RO-CCSD(T)/aug-cc-pVTZ & 1.439 & 1.439 & 1.075 & 135.00 &\alert{RO-CCSD(T)/aug-cc-pVTZ} \fnm[2] & 1.439 & 1.439 & 1.075 & 135.00
\end{tabular} \end{tabular}
\end{ruledtabular} \end{ruledtabular}
\fnt[1]{Angle between the \ce{C-H} bond and the \ce{C=C} bond.} \fnt[1]{Angle between the \ce{C-H} bond and the \ce{C=C} bond.}
\fnt[2]{From Ref.~\onlinecite{Manohar_2008}.} \fnt[2]{This work.}
\fnt[3]{From Ref.~\onlinecite{Manohar_2008}.}
\end{table} \end{table}
\end{squeezetable} \end{squeezetable}
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