working on intro

Manuscript/ExPerspective.tex

@@ -1,5 +1,5 @@
 \documentclass[aps,prb,reprint,noshowkeys,superscriptaddress]{revtex4-1}
-\usepackage{graphicx,dcolumn,bm,xcolor,microtype,multirow,amscd,amsmath,amssymb,amsfonts,physics,mhchem,longtable,wrapfig,txfonts}
+\usepackage{graphicx,dcolumn,bm,xcolor,microtype,multirow,amscd,amsmath,amssymb,amsfonts,physics,mhchem,longtable,pifont,wrapfig,txfonts}
 
 \usepackage{natbib}
 \usepackage[extra]{tipa}
@@ -25,6 +25,9 @@
 \newcommand{\trashDJ}[1]{\textcolor{purple}{\sout{#1}}}
 \newcommand{\trashAS}[1]{\textcolor{brown}{\sout{#1}}}
 
+\newcommand{\cmark}{\color{green}{\text{\ding{51}}}}
+\newcommand{\xmark}{\color{red}{\text{\ding{55}}}}
+
 \usepackage{hyperref}
 \hypersetup{
     colorlinks=true,
@@ -86,30 +89,70 @@ iv) what we believe could be the future developments in the field.
 %%% INTRODUCTION %%%
 %%%%%%%%%%%%%%%%%%%%
 The accurate modelling of excited-state properties from \textit{ab initio} quantum chemistry methods is a challenging yet self-proclaimed ambition of the electronic structure theory community that will certainly keep us busy for (at the very least) the next few decades to come.
-Of particular interest is the access to precise excitation energies, \ie, the energy difference between the ground and excited states.
+Of particular interest is the access to precise excitation energies, \ie, the energy difference between the ground and excited states, and their intimate link with photochemical processes and photochemistry in general.
 The factors that make this quest for high accuracy particularly delicate are very diverse.
 First of all (and maybe surprisingly), it is, in most cases, tricky to obtain reliable and accurate experimental data that one can straightforwardly compare to theoretical values.
 In the case of vertical excitation energies, \ie, excitation energies at a fixed geometry, band maxima does not usually match theoretical values as one needs to take into account the geometric relaxation and the zero-point vibrational energy motion.
 Even more problematic, experimental spectra might not available in gas phase, and in the worst-case scenario, wrong assignments may occur.
+For a faithful comparison between theory and experimental, the so-called 0-0 energies are definitely a better playground.
+However, they require from a theoretical point of view access to the optimized excited-state geometry as well as its harmonic vibration frequencies.
 
-Excited states are usually extremely close in energy and can have very different nature ($\pi \ra \pi^*$, $n \ra \pi^*$, charge transfer, double excitations, Rydberg states, etc).
+What makes also excited states fascinating and challenging at the same time are usually extremely close in energy and can have very different nature ($\pi \ra \pi^*$, $n \ra \pi^*$, charge transfer, double excitations, Rydberg states, etc).
 Therefore one needs --- in principle at least ---  a computational method providing a balanced theoretical treatment of all these excited states.
 And let's be honest, none of the existing methods does provide this.
 
-If you were asking for the perfect excited state method for Christmas, what would you (realistically) ask for?
+If you were asking for the perfect excited-state method for Christmas, what would you (realistically) ask for?
 The requirement for the ``perfect'' theoretical model would be:
 i) balanced treatment of excited states with different character.
 ii) chemically accurate excitation energies ie error smaller than 1 kcal/mol or $0.05$ eV.
-iii) other properties (such as oscillator strength, dipole moment,  optimization for excited tstae geometries (analytical highliy desirable)
-iv) Minimal user input requirement (black box method) and minimization of chemical intuition in order not to bias the results.
+iii) other properties (such as oscillator strength, dipole moment, optimisation for excited state geometries (analytical highly desirable)
+iv) Minimal user input requirement (black box method) and minimisation of chemical intuition in order not to bias the results.
 v) Low computational scaling with respect to system size and small memory footprint.
+In summary, each method has its own strengths and weaknesses, and none of them is able to provide accurate and reliable excitation energies in all scenarios. 
 
 Although people usually don't really like reading, reviewing or even the idea of benchmark studies, these are definitely essential for the validation of existing theoretical methods and to understand their strengths and, more importantly, their limitations.
 
+
+There is a clear need for computationally inexpensive electronic structure theory methods which can model accurately excited-state energetics and their corresponding properties. 
+Although time-dependent density-functional theory (TD-DFT) and the Bethe-Salpeter equation (BSE) formalism have emerged as powerful tools for computing excitation energies, fundamental deficiencies remain to be solved. 
+For example, the simplest and most widespread approximation in state-of-the-art electronic structure programs where TD-DFT and BSE are implemented consists in neglecting memory effects. 
+This has drastic consequences such as, for example, the complete absence of double excitations from the TD-DFT and BSE spectra.
+
+%%% TABLE I %%%
+\begin{table}
+\caption{Scaling of various excited state methods.
+$N$ is the number of basis functions.}
+\label{tab:method}
+\begin{ruledtabular}
+\begin{tabular}{lcccl}
+	Method			&	Scaling		&	Oscillator 	&	Analytic 		&	Software	\\
+					&				&	strength	&	gradient		&		\\
+	\hline
+	TD-DFT			&	$N^4$		&	\cmark		&	\cmark			&	GAUSSIAN	\\
+	BSE@GW			&	$N^6$		&	\cmark		&	\xmark			&	FIESTA		\\
+	CIS(D)			&	$N^7$		&	\cmark		&	\cmark			&	DALTON		\\
+	CIS(D$_\infty$)	&	$N^7$		&	\cmark		&	\cmark			&	MRCC		\\
+	CC2				&	$N^6$		&	\cmark		&	\cmark			&	DALTON		\\
+	CC3				&	$N^7$		&	\xmark		&	\xmark			&	DALTON		\\
+	ADC(2)			&	$N^7$		&	\cmark		&	\cmark			&	Q-CHEM		\\
+	ADC(3)			&	$N^7$		&	\cmark		&	\xmark			&	Q-CHEM		\\
+	EOM-CCSD		&	$N^7$		&	\cmark		&	\cmark			&	DALTON		\\
+	STEOM-CCSD		&	$N^7$		&	\cmark		&	\xmark			&	ORCA		\\
+	EOM-CCSDR(3)	&	$N^7$		&	\cmark		&	\cmark			&	DALTON		\\
+	EOM-CCSDT-3		&	$N^7$		&	\xmark		&	\xmark			&	CFOUR		\\
+	EOM-CCSDT		&	$N^8$		&	\xmark		&	\xmark			&	CFOUR		\\
+	EOM-CCSDTQ		&	$N^{10}$	&	\xmark		&	\xmark			&	MRCC		\\
+	EOM-CCSDTQP		&	$N^{12}$	&	\xmark		&	\xmark			&	MRCC		\\
+	CASPT2			&	$e^N$		&	\cmark		&	\cmark			&	MOLPRO		\\
+	NEVPT2			&	$e^N$		&	\xmark		&	\xmark			&	MOLPRO		\\
+	sCI				&	$e^N$		&	\xmark		&	\xmark			&	QP2			\\
+\end{tabular}
+\end{ruledtabular}
+\end{table}
 %%%%%%%%%%%%%%%%%%%
 %%% ROOS' GROUP %%%
 %%%%%%%%%%%%%%%%%%%
-Roos' group probably kick started the whole thing thanks to their method CASPT2.
+Roos' group probably kick started the whole thing thanks to their CASPT2 method.
 
 %%%%%%%%%%%%%%%%%%%%%
 %%% THIEL'S GROUP %%%

README.md

@@ -0,0 +1 @@
+Come on Denis, you can do it!