From c461645933c5273c1c6f0389f5ec7977217b5e17 Mon Sep 17 00:00:00 2001 From: Pierre-Francois Loos Date: Mon, 11 Apr 2022 16:46:07 +0200 Subject: [PATCH] submitted to JPCA --- Manuscript/CBD.tex | 4 ++-- Manuscript/Cover_Letter/CoverLetter.tex | 13 ++++++++++++- 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/Manuscript/CBD.tex b/Manuscript/CBD.tex index 11d6d76..5075a9d 100644 --- a/Manuscript/CBD.tex +++ b/Manuscript/CBD.tex @@ -1,8 +1,8 @@ \documentclass[aip,jcp,reprint,noshowkeys,superscriptaddress]{revtex4-1} \usepackage{graphicx,dcolumn,bm,xcolor,microtype,multirow,amscd,amsmath,amssymb,amsfonts,physics,longtable,wrapfig,txfonts} \usepackage[version=4]{mhchem} -%\usepackage{natbib} -%\bibliographystyle{achemso} +\usepackage{natbib} +\bibliographystyle{achemso} \usepackage[utf8]{inputenc} \usepackage[T1]{fontenc} \usepackage{txfonts} diff --git a/Manuscript/Cover_Letter/CoverLetter.tex b/Manuscript/Cover_Letter/CoverLetter.tex index cdbb43b..0b2bd46 100644 --- a/Manuscript/Cover_Letter/CoverLetter.tex +++ b/Manuscript/Cover_Letter/CoverLetter.tex @@ -1,5 +1,5 @@ \documentclass[10pt]{letter} -\usepackage{UPS_letterhead,xcolor,mhchem,mathpazo,ragged2e} +\usepackage{UPS_letterhead,xcolor,mhchem,ragged2e} \newcommand{\alert}[1]{\textcolor{red}{#1}} \definecolor{darkgreen}{HTML}{009900} @@ -15,6 +15,17 @@ Please find enclosed our manuscript entitled \textit{``Reference Energies for Cyclobutadiene: Automerization and Excited States''}, which we would like you to consider as a Regular Article in the \textit{Journal of Physical Chemistry A}. This contribution has never been submitted in total nor in parts to any other journal, and has been seen and approved by all authors. +The cyclobutadiene molecule has been a real challenge for both experimental and theoretical chemistry for many decades. +In particular, cyclobutadiene is a well-known playground for theoretical chemists and is particularly suitable to test ground- and excited-state methods. +In the $D_{2h}$ symmetry, the ground state has a weak multi-configurational character with well-separated frontier orbitals that can be described by single-reference methods. +However, in the $D_{4h}$ symmetry, the ground state is a diradical that has two degenerate singly occupied frontier orbitals. + +In the present paper, we assess a larger number of computational methods on the automerization barrier and the vertical excitation energies of cyclobutadiene in its square ($D_{4h}$) and rectangular ($D_{2h}$) geometries, for which we have defined theoretical best estimates based on high-level coupled-cluster calculations. +In particular, selected configuration interaction, multi-reference perturbation theory (CASSCF, CASPT2, and NEVPT2), and coupled-cluster calculations are performed. +These wave function methods are compared with the cheaper spin-flip formalism which is tested within TD-DFT and the ADC scheme. + +Several important take-home messages are extracted from the present study, such as the excellent performance of hybrid functionals with a large amount of exact exchange, the outstanding accuracy of the ADC schemes, the importance of the $\sigma$-$\pi$ coupling in multi-configurational calculations, and the importance of quadruple excitations to reach high accuracy in coupled-cluster theory. + We suggest David Casanova, Miquel Huix-Rotllant, Michael Filatov, Donald Truhlar, and Andreas Dreuw as potential referees. We look forward to hearing from you.