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Anthony Scemama 2024-06-25 09:43:22 +02:00
parent 0643fb7008
commit 809d0d860e
2 changed files with 32 additions and 1 deletions

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@ -578,3 +578,33 @@ swh:1:dir:6d82ae7ac757c78d7720dd89dfa52d7a453d2f68;origin=https://github.com/Qua
publisher = {American Physical Society}, publisher = {American Physical Society},
doi = {10.1103/RevModPhys.71.1267} doi = {10.1103/RevModPhys.71.1267}
} }
@article{purvis_1982,
author = {Purvis, George D. and Bartlett, Rodney J.},
title = {{A full coupled{-}cluster singles and doubles model: The inclusion of disconnected triples}},
journal = {J. Chem. Phys.},
volume = {76},
number = {4},
pages = {1910--1918},
year = {1982},
month = feb,
issn = {0021-9606},
publisher = {AIP Publishing},
doi = {10.1063/1.443164}
}
@article{scuseria_1988,
author = {Scuseria, Gustavo E. and Janssen, Curtis L. and Schaefer, Henry F.},
title = {{An efficient reformulation of the closed{-}shell coupled cluster single and double excitation (CCSD) equations}},
journal = {J. Chem. Phys.},
volume = {89},
number = {12},
pages = {7382--7387},
year = {1988},
month = dec,
issn = {0021-9606},
publisher = {AIP Publishing},
doi = {10.1063/1.455269}
}

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@ -129,7 +129,7 @@ The CC framework starts with a parameterized wave function, typically referred t
\end{equation} \end{equation}
where $\ket{\Phi}$ is the reference determinant, and $\hat{T}$ is the cluster operator representing single, double, triple, and higher excitations on top of the reference wave function.\cite{crawford_2000,bartlett_2007,shavitt_2009} where $\ket{\Phi}$ is the reference determinant, and $\hat{T}$ is the cluster operator representing single, double, triple, and higher excitations on top of the reference wave function.\cite{crawford_2000,bartlett_2007,shavitt_2009}
Coupled Cluster with Singles and Doubles (CCSD) includes single and double particle-hole excitations and represents the most commonly used variant of CC theory. CCSD is exact for two-electron systems and includes all terms Coupled Cluster with Singles and Doubles\cite{purvis_1982,scuseria_1988} (CCSD) includes single and double particle-hole excitations and represents the most commonly used variant of CC theory. CCSD is exact for two-electron systems and includes all terms
from third order perturbation theory and beyond. from third order perturbation theory and beyond.
Coupled Cluster with Singles, Doubles, and perturbative Triples (CCSD(T)) incorporates a perturbative correction to the CCSD energy to account for some higher-order correlation effects, and has been termed in the literature as the gold standard of quantum chemistry.\cite{raghavachari_1989} Coupled Cluster with Singles, Doubles, and perturbative Triples (CCSD(T)) incorporates a perturbative correction to the CCSD energy to account for some higher-order correlation effects, and has been termed in the literature as the gold standard of quantum chemistry.\cite{raghavachari_1989}
CCSD(T) has demonstrated exceptional accuracy and reliability, making it one of the preferred choices for benchmark calculations and highly accurate predictions. CCSD(T) has demonstrated exceptional accuracy and reliability, making it one of the preferred choices for benchmark calculations and highly accurate predictions.
@ -210,6 +210,7 @@ To reduce the fluctuations of the statistical estimator, we apply importance sam
P^{abc} = \frac{1}{\mathcal{N}} \frac{1}{\max \left(\epsilon_{\min}, \epsilon_a + \epsilon_b + \epsilon_c \right)} P^{abc} = \frac{1}{\mathcal{N}} \frac{1}{\max \left(\epsilon_{\min}, \epsilon_a + \epsilon_b + \epsilon_c \right)}
\end{equation} \end{equation}
where $\mathcal{N}$ normalizes the sum such that $\sum_{abc} P^{abc} = 1$, and $\epsilon_{\min}$ is an arbitrary minimal denominator to ensure that $P^{abc}$ does not diverge. In our calculations, we have set $\epsilon_{\min}$ to 0.2~a.u. where $\mathcal{N}$ normalizes the sum such that $\sum_{abc} P^{abc} = 1$, and $\epsilon_{\min}$ is an arbitrary minimal denominator to ensure that $P^{abc}$ does not diverge. In our calculations, we have set $\epsilon_{\min}$ to 0.2~a.u.
\anthony{The algorithm is not very sensitive to the value of $\epsilon_{\min}$ as long as it is taken within reasonable bounds, in the range of the level-shift parameter in SCF calculations.}
The perturbative contribution is then evaluated as an average over $M$ samples The perturbative contribution is then evaluated as an average over $M$ samples
\begin{equation} \begin{equation}
E_{(T)} = \left\langle \frac{E^{abc}}{P^{abc}} \right \rangle_{P^{abc}} = E_{(T)} = \left\langle \frac{E^{abc}}{P^{abc}} \right \rangle_{P^{abc}} =