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Manuscript/ExPerspective.bib
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@ -1,7 +1,7 @@
%% This BibTeX bibliography file was created using BibDesk.
%% http://bibdesk.sourceforge.net/
%% Created for Pierre-Francois Loos at 2019-11-16 13:45:05 +0100
%% Created for Pierre-Francois Loos at 2019-11-18 11:10:52 +0100
%% Saved with string encoding Unicode (UTF-8)
@ -1794,13 +1794,12 @@
Year = {2013},
Bdsk-Url-1 = {https://arxiv.org/abs/1311.6244}}
@book{Pen19,
author = {Peng, Ivy B. and Gokhale, Maya B. and Green, Eric W.},
title = {{System evaluation of the Intel optane byte-addressable NVM}},
year = {2019},
month = {Sep},
isbn = {978-1-4503-7206-0},
publisher = {ACM},
doi = {10.1145/3357526.3357568}
}
Author = {Peng, Ivy B. and Gokhale, Maya B. and Green, Eric W.},
Doi = {10.1145/3357526.3357568},
Isbn = {978-1-4503-7206-0},
Month = {Sep},
Publisher = {ACM},
Title = {{System evaluation of the Intel optane byte-addressable NVM}},
Year = {2019},
Bdsk-Url-1 = {https://doi.org/10.1145/3357526.3357568}}

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Manuscript/ExPerspective.tex
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@ -145,7 +145,6 @@ The typical error range or estimate for single excitations is also provided as a
%**************
Before detailing some key past and present contributions towards the obtention of highly accurate excitation energies, we start by giving a historical overview of the various excited-state \textit{ab initio} methods that have emerged in the last fifty years.
Interestingly, for pretty much every single method, the theory was derived much earlier than their actual implementation in electronic structure software packages (same applies to the analytic gradients when available).
%Here, we only mention methods that, we think, ended up becoming mainstream.
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%%% POPLE'S GROUP %%%
@ -182,7 +181,7 @@ Despite all of this, TD-DFT is still nowadays the most employed excited-state me
%%%%%%%%%%%%%%%%%%
%%% CC METHODS %%%
%%%%%%%%%%%%%%%%%%
Thanks to the development of coupled cluster (CC) response theory, \cite{Koc90} and the huge growth of computational ressources, equation-of-motion coupled cluster with singles and doubles (EOM-CCSD) \cite{Sta93} became mainstream in the 2000's.
Thanks to the development of coupled cluster (CC) response theory, \cite{Koc90} and the huge growth of computational resources, equation-of-motion coupled cluster with singles and doubles (EOM-CCSD) \cite{Sta93} became mainstream in the 2000's.
EOM-CCSD gradients were also quickly available. \cite{Sta95}
With EOM-CCSD, it is not unusual to have errors as small as $0.1$ eV, and a typical overestimation of the vertical transition energies.
Its third-order version, EOM-CCSDT, was also implemented and provides, at a significantly higher cost, high accuracy for single excitations. \cite{Nog87}
@ -322,23 +321,25 @@ For someone who has never worked with SCI methods, it might be surprising to see
This is mainly due to some specific choices in terms of implementation as explained below.
Indeed, to keep up with Moore's ``Law'' in the early 2000's, the processor designers had no other choice than to propose multi-core chips to avoid an explosion of the energy requirements.
Increasing the number of floating-point operations per second (flops/s) by doubling the number of CPU cores only requires to double the required energy, while doubling the frequency multiplies the required energy by a factor close to 8.
This bifuraction in hardware design implied a \emph{change of paradigm}\cite{Sut05} in the implementation and design of computational algorithms. A large degree of parallelism is now required to benefit from a significant acceleration.
Fifteen years later, the community has made a significant effort to redesign the methods with parallel-friendly algorithms.\cite{Val10,Cle10,Gar17b,Pen16,Kri13,Sce13}
This bifurcation in hardware design implied a \emph{change of paradigm} \cite{Sut05} in the implementation and design of computational algorithms. A large degree of parallelism is now required to benefit from a significant acceleration.
Fifteen years later, the community has made a significant effort to redesign the methods with parallel-friendly algorithms. \cite{Val10,Cle10,Gar17b,Pen16,Kri13,Sce13}
In particular, the change of paradigm to reach FCI accuracy with SCI methods came
from the use of determinant-driven algorithms which were considered for long as inefficient
with respect to integral-driven algorithms.
The first important element making these algorithms efficient is the introduction of new bit manipulation instructions (BMI) in the hardware that enable an extremely fast evaluation of Slater-Condon rules\cite{Sce13b} for the direct calculation of
The first important element making these algorithms efficient is the introduction of new bit manipulation instructions (BMI) in the hardware that enable an extremely fast evaluation of Slater-Condon rules \cite{Sce13b} for the direct calculation of
the Hamiltonian matrix elements over arbitrary determinants.
Then massive parallelism can be harnessed to compute the second-order perturbative correction with semi-stochatic algorithms,\cite{Gar17b,Sha17} and perform the sparse matrix multiplications required in Davidson's algorithm to find the eigenvectors associated with the lowest eigenvalues.
Block-Davidson methods can require a large amount of memory, and the recent introduction of byte-addressable non-volatile memory as a new tier in the memory hierarchy\cite{Pen19} will enable SCI calculations on larger molecules.
Then massive parallelism can be harnessed to compute the second-order perturbative correction with semi-stochatic algorithms, \cite{Gar17b,Sha17} and perform the sparse matrix multiplications required in Davidson's algorithm to find the eigenvectors associated with the lowest eigenvalues.
Block-Davidson methods can require a large amount of memory, and the recent introduction of byte-addressable non-volatile memory as a new tier in the memory hierarchy \cite{Pen19} will enable SCI calculations on larger molecules.
The next generation of supercomputers is going to generalize the presence of accelerators (graphical processing units, GPUs), leading to a new software crisis.
Fortunately, some authors have already prepared this transition.\cite{Dep11,Kim18,Sny15,Ufi08,Kal17}
Fortunately, some authors have already prepared this transition. \cite{Dep11,Kim18,Sny15,Ufi08,Kal17}
%%%%%%%%%%%%%%%%%%
%%% CONCLUSION %%%
%%%%%%%%%%%%%%%%%%
As concluding remarks, we would like to say that, even though Thiel's group contribution is pretty awesome, what we have done is not bad either.
Thanks to new technological advances, we hope to be able to push further our quest to highly accurate excitation energies in years to come.
As concluding remarks, we would like to highlight once again the major contribution brought by Thiel's group in an effort to define broad and accurate benchmark sets for excited states. \cite{Sch08,Sil08,Sau09,Sil10b,Sil10c}
Following their footsteps, we have recently proposed a larger, even more accurate set of transitions energies for various types of excited states (including double excitations). \cite{Loo18a,Loo19c,Loo20}
This was made possible thanks to a technological renaissance of SCI methods which can now routinely produce near-FCI excitation energies for small- and medium-size organic molecules. \cite{Chi18,Gar18,Gar19}
We hope that new technological advances will enable us to push further our quest to highly accurate excitation energies in years to come.
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%%% ACKNOWLEDGEMENTS %%%