The convergence behavior of connected triples correlation energy in CCSD(T) and CC3 calculations with (aug-)cc-pVXZ basis sets has been accurately described in terms of a power law of the type E(X)=E(infinity)+AX(-4). Calculations ranging from double-Z through septuple-Z attest the validity of this X(-4) convergence model. Extrapolations generated from (X-1,X)-Z calculations yield energies of nearly (X+1)-Z quality. Typically, the fraction of triples correlation energy recovered is 0.92+/-0.05 in (D,T) extrapolations; 0.98+/-0.01 in (T,Q) extrapolations; 1.0002+/-0.0012 in (Q,5) extrapolations; and 0.9995+/-0.0005 in (5,6) extrapolations.
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http://dx.doi.org/10.1063/1.1821495 | DOI Listing |
J Chem Phys
January 2025
Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway.
Traditionally, excitation energies in coupled-cluster (CC) theory have been calculated by solving the CC Jacobian eigenvalue equation. However, based on our recent work [Jørgensen et al., Sci.
View Article and Find Full Text PDFJ Phys Chem A
January 2025
Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China.
This study investigates the equilibrium geometries of four different Se isomers using the coupled cluster single and double perturbative (CCSD(T)) method, extrapolating to the complete basis sets. The ground-state geometry of the Se isomer with the C structure (2.8715 Å, 2.
View Article and Find Full Text PDFJ Chem Phys
January 2025
Department of Physics, AlbaNova University Center, Stockholm University, S-106 91 Stockholm, Sweden.
In this work, we present a non-orthogonal configuration interaction (NOCI) approach to address the rotational corrections in multicomponent quantum chemistry calculations where hydrogen nuclei and electrons are described with orbitals under Hartree-Fock (HF) and density functional theory (DFT) frameworks. The rotational corrections are required in systems such as diatomic (HX) and nonlinear triatomic molecules (HXY), where localized broken-symmetry nuclear orbitals have a lower energy than delocalized orbitals with the correct symmetry. By restoring rotational symmetry with the proposed NOCI approach, we demonstrate significant improvements in proton binding energy predictions at the HF level, with average rotational corrections of 0.
View Article and Find Full Text PDFMolecules
December 2024
Department of Chemical and Materials Engineering, Lyuliang University, Lishi 033001, China.
We studied the boron-based composite cluster BAl doped with Al atoms. The global minimum structure of the BAl cluster is a three-layer structure, consisting of three parts: an Al unit, a B ring and an isolated Al atom. Charge calculations analysis shows that the cluster can be expressed as [Al][B][Al], has 6π/6σ double aromaticity and follows the (4+2) Hückel rule.
View Article and Find Full Text PDFACS Omega
December 2024
Faculty of Health Science, University of Ss. Cyril and Methodius, 91701 Trnava, Slovakia.
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