Journal ArticleDOI
A state-specific approach to multireference coupled electron-pair approximation like methods: development and applications.
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TLDR
A suite of physically motivated coupled electron-pair approximations (SS-MRCEPA) like methods, which are designed to capture the essential strength of the parent SS-MRCC method without significant sacrificing its accuracy, are suggested and explored.Abstract:
The traditional multireference (MR) coupled-cluster (CC) methods based on the effective Hamiltonian are often beset by the problem of intruder states, and are not suitable for studying potential energy surface (PES) involving real or avoided curve crossing. State-specific MR-based approaches obviate this limitation. The state-specific MRCC (SS-MRCC) method developed some years ago [Mahapatra et al., J. Chem. Phys. 110, 6171 (1999)] can handle quasidegeneracy of varying degrees over a wide range of PES, including regions of real or avoided curve-crossing. Motivated by its success, we have suggested and explored in this paper a suite of physically motivated coupled electron-pair approximations (SS-MRCEPA) like methods, which are designed to capture the essential strength of the parent SS-MRCC method without significant sacrificing its accuracy. These SS-MRCEPA theories, like their CC counterparts, are based on complete active space, treat all the reference functions on the same footing and provide a descrip...read more
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Software news and update MOLCAS 7 : The Next Generation
Francesco Aquilante,Luca De Vico,Nicolas Ferré,Giovanni Ghigo,Per-Åke Malmqvist,Pavel Neogrády,Thomas Bondo Pedersen,Michal Pitonak,Michal Pitonak,Markus Reiher,Björn O. Roos,Luis Serrano-Andrés,Miroslav Urban,Valera Veryazov,Roland Lindh +14 more
TL;DR: The Cholesky decomposition method applied to some quantum chemical methods is described, and the ElectroStatic Potential Fitted scheme, a version of a quantum mechanics/molecular mechanics hybrid method implemented in MOLCAS, is described and discussed.
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Multiconfiguration Self-Consistent Field and Multireference Configuration Interaction Methods and Applications
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Multireference nature of chemistry: the coupled-cluster view.
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Coupling term derivation and general implementation of state-specific multireference coupled cluster theories
TL;DR: Comparison with experimental data shows that the Mukherjee method is generally superior to the Brillouin-Wigner theory in predicting energies, structures, and vibrational frequencies.
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High-order excitations in state-universal and state-specific multireference coupled cluster theories: model systems.
TL;DR: High-order excitations have been studied in three multireference couple cluster theories built on the wave operator formalism and the BW and Mk methods are found to provide more accurate results than the state-universal SU approach at all levels of truncation of the cluster operator.
References
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Journal ArticleDOI
A full coupled‐cluster singles and doubles model: The inclusion of disconnected triples
TL;DR: The coupled cluster singles and doubles model (CCSD) as discussed by the authors is derived algebraically, presenting the full set of equations for a general reference function explicitly in spin-orbital form, and the computational implementation of the CCSD model, which involves cubic and quartic terms, is discussed and results are compared with full CI calculations for H2O and BeH2.
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Gaussian Basis Functions for Use in Molecular Calculations. III. Contraction of (10s6p) Atomic Basis Sets for the First‐Row Atoms
TL;DR: In this paper, the effects of contraction on the energies and one-electron properties of the water and nitrogen molecules were investigated, and the authors obtained principles which can be used to predict optimal contraction schemes for other systems without the necessity of such exhaustive calculations.
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On the Correlation Problem in Atomic and Molecular Systems. Calculation of Wavefunction Components in Ursell-Type Expansion Using Quantum-Field Theoretical Methods
TL;DR: In this article, a method for the calculation of the matrix elements of the logarithm of an operator which gives the exact wavefunction when operating on the wavefunction in the one-electron approximation is proposed.
BookDOI
Methods of Electronic Structure Theory
TL;DR: In this paper, the authors present a method for determining configuration interaction wave functions for the Electronic States of Atoms and Molecules: the Vector Method, which is a general computer program for ab initio calculations.
Journal ArticleDOI
Coupled-cluster approach to molecular structure and spectra: a step toward predictive quantum chemistry
TL;DR: Etude de l'une des limitations dans la solution of l'equation de Schrodinger a savoir, le probleme de la correlation electronique et d'une nouvelle approche de sa resolution, la theorie des amas couples as mentioned in this paper.