The divide–expand–consolidate coupled cluster scheme

We have presented a multi-layer implementation of the equation of motion coupled-cluster method for the electron affinity, based on local and pair natural orbitals. The method gives consistent accuracy for both localized and delocalized anionic states. It results in many fold speedup in computational timing as compared to the canonical and DLPNO based implementation of the EA-EOM-CCSD method. We have also developed an explicit fragment-based approach which can lead to even higher speed-up with little loss in accuracy. The multi-layer method can be used to treat the environmental effect of both bonded and non-bonded nature on the electron attachment process in large molecules.<br>

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The X40x10 Halogen Bonding Benchmark Revisited: Surprising Importance of (n-1)d Subvalence Correlation

10.26434/chemrxiv.5580007.v1 ◽

2017 ◽

Author(s):

Manoj Kumar Kesharwani ◽

Nitai Sylvetsky ◽

Debashree Manna ◽

Jan M.L. Martin

Keyword(s):

Dissociation Energy ◽

Noncovalent Interactions ◽

Halogen Bonding ◽

Coupled Cluster ◽

Dissociation Energies ◽

Iodine Species ◽

Explicitly Correlated ◽

High Level ◽

Cluster Methods ◽

Small Separation

<p>We have re-evaluated the X40x10 benchmark for halogen bonding using conventional and explicitly correlated coupled cluster methods. For the aromatic dimers at small separation, improved CCSD(T)–MP2 “high-level corrections” (HLCs) cause substantial reductions in the dissociation energy. For the bromine and iodine species, (n-1)d subvalence correlation increases dissociation energies, and turns out to be more important for noncovalent interactions than is generally realized. As in previous studies, we find that the most efficient way to obtain HLCs is to combine (T) from conventional CCSD(T) calculations with explicitly correlated CCSD-F12–MP2-F12 differences.</p>

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Excitonic Coupled-cluster Theory: Part I, General Formalism

10.26434/chemrxiv.5330773.v2 ◽

2017 ◽

Cited By ~ 1

Author(s):

Yuhong Liu ◽

Anthony Dutoi

Keyword(s):

Electron Correlation ◽

Degrees Of Freedom ◽

Model Systems ◽

Coupled Cluster ◽

Effective Hamiltonian ◽

Coupled Cluster Theory ◽

Cluster Theory ◽

Companion Article ◽

High Level ◽

Fragment Interaction

<div> <div>A shortcoming of presently available fragment-based methods is that electron correlation (if included) is described at the level of individual electrons, resulting in many redundant evaluations of the electronic relaxations associated with any given fluctuation. A generalized variant of coupled-cluster (CC) theory is described, wherein the degrees of freedom are fluctuations of fragments between internally correlated states. The effects of intra-fragment correlation on the inter-fragment interaction is pre-computed and permanently folded into the effective Hamiltonian. This article provides a high-level description of the CC variant, establishing some useful notation, and it demonstrates the advantage of the proposed paradigm numerically on model systems. A companion article shows that the electronic Hamiltonian of real systems may always be cast in the form demanded. This framework opens a promising path to build finely tunable systematically improvable methods to capture precise properties of systems interacting with a large number of other systems. </div> </div>

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Excitonic Coupled-cluster Theory: Part I, General Formalism

10.26434/chemrxiv.5330773.v1 ◽

2017 ◽

Author(s):

Yuhong Liu ◽

Anthony Dutoi

Keyword(s):

Electron Correlation ◽

Degrees Of Freedom ◽

Model Systems ◽

Coupled Cluster ◽

Effective Hamiltonian ◽

Coupled Cluster Theory ◽

Cluster Theory ◽

Companion Article ◽

High Level ◽

Fragment Interaction

<div> <div>A shortcoming of presently available fragment-based methods is that electron correlation (if included) is described at the level of individual electrons, resulting in many redundant evaluations of the electronic relaxations associated with any given fluctuation. A generalized variant of coupled-cluster (CC) theory is described, wherein the degrees of freedom are fluctuations of fragments between internally correlated states. The effects of intra-fragment correlation on the inter-fragment interaction is pre-computed and permanently folded into the effective Hamiltonian. This article provides a high-level description of the CC variant, establishing some useful notation, and it demonstrates the advantage of the proposed paradigm numerically on model systems. A companion article shows that the electronic Hamiltonian of real systems may always be cast in the form demanded. This framework opens a promising path to build finely tunable systematically improvable methods to capture precise properties of systems interacting with a large number of other systems. </div> </div>

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