Coupled cluster

About: Coupled cluster is a research topic. Over the lifetime, 6280 publications have been published within this topic receiving 301055 citations.

Accurate Ionization Potentials and Electron Affinities of Acceptor Molecules I. Reference Data at the CCSD(T) Complete Basis Set Limit.

Abstract: In designing organic materials for electronics applications, particularly for organic photovoltaics (OPV), the ionization potential (IP) of the donor and the electron affinity (EA) of the acceptor play key roles. This makes OPV design an appealing application for computational chemistry since IPs and EAs are readily calculable from most electronic structure methods. Unfortunately reliable, high-accuracy wave function methods, such as coupled cluster theory with single, double, and perturbative triples [CCSD(T)] in the complete basis set (CBS) limit are too expensive for routine applications to this problem for any but the smallest of systems. One solution is to calibrate approximate, less computationally expensive methods against a database of high-accuracy IP/EA values; however, to our knowledge, no such database exists for systems related to OPV design. The present work is the first of a multipart study whose overarching goal is to determine which computational methods can be used to reliably compute IP...

Heisenberg antiferromagnet on the kagome lattice with arbitrary spin: A higher-order coupled cluster treatment

Abstract: Starting with the 3√×3√ and the q=0 states as reference states, we use the coupled cluster method to high orders of approximation to investigate the ground state of the Heisenberg antiferromagnet on the kagome lattice for spin quantum numbers s=1/2, 1, 3/2, 2, 5/2, and 3. Our data for the ground-state energy for s=1/2 are in good agreement with recent large-scale density-matrix renormalization group and exact diagonalization data. We find that the ground-state selection depends on the spin quantum number s. While for the extreme quantum case, s=1/2, the q=0 state is energetically favored by quantum fluctuations, for any s>1/2 the 3√×3√ state is selected. For both the 3√×3√ and the q=0 states the magnetic order is strongly suppressed by quantum fluctuations. Within our coupled cluster method we get vanishing values for the order parameter (sublattice magnetization) M for s=1/2 and s=1, but (small) nonzero values for M for s>1. Using the data for the ground-state energy and the order parameter for s=3/2, 2, 5/2, and 3 we also estimate the leading quantum corrections to the classical values.

Communication: Resolving the three-body contribution to the lattice energy of crystalline benzene: Benchmark results from coupled-cluster theory

Abstract: Coupled-cluster theory including single, double, and perturbative triple excitations [CCSD(T)] has been applied to trimers that appear in crystalline benzene in order to resolve discrepancies in the literature about the magnitude of non-additive three-body contributions to the lattice energy. The present results indicate a non-additive three-body contribution of 0.89 kcal mol−1, or 7.2% of the revised lattice energy of −12.3 kcal mol−1. For the trimers for which we were able to compute CCSD(T) energies, we obtain a sizeable difference of 0.63 kcal mol−1 between the CCSD(T) and MP2 three-body contributions to the lattice energy, confirming that three-body dispersion dominates over three-body induction. Taking this difference as an estimate of three-body dispersion for the closer trimers, and adding an Axilrod-Teller-Muto estimate of 0.13 kcal mol−1 for long-range contributions yields an overall value of 0.76 kcal mol−1 for three-body dispersion, a significantly smaller value than in several recent studies.

Coupled Cluster Theory with Emphasis on Selected New Developments

Abstract: Coupled cluster (CC) methods for the description of the correlated motion of electrons and nuclei are reviewed with emphasis on selected new initiatives. The basic aspects of standard electronic CC theory are described including the rationale behind the most widely used methods like coupled cluster singles and doubles (CCSD) and the CCSD(T) approach. The hierarchy of coupled cluster models consisting of coupled cluster singles (CCS), CC2, CCSD and CC3 is also described. A brief account of the theory behind the calculation of molecular properties using CC methods, and the description of response properties and excited states using CC response theory is followed by a discussion of the use of CC theory in the context of effective models for describing molecules in solution. In another part of the review we consider recent initiatives aimed at the development of coupled cluster methods for describing the correlated motion of the atomic nuclei. A recently developed second quantization formulation of many-mode dynamics for distinguishable degrees of freedom forms the basis for developing new quantum dynamical methods in particular vibrational coupled cluster (VCC) methods. The VCC theory is reviewed and discussed in comparison with vibrational configuration interaction (VCI), and vibrational Moller–Plesset (VMP) perturbation theory. The review concludes with a discussion of some important future research topics

Symmetry broken and restored coupled-cluster theory: I. Rotational symmetry and angular momentum

Abstract: We extend coupled-cluster (CC) theory performed on top of a Slater determinant breaking rotational symmetry to allow for the exact restoration of the angular momentum at any truncation order. The main objective relates to the description of near-degenerate finite quantum systems with an open-shell character. As such, the newly developed many-body formalism offers a wealth of potential applications and further extensions dedicated to the ab initio description of, e.g., doubly open-shell atomic nuclei and molecule dissociation. The formalism, which encompasses both single-reference CC theory and projected Hartree–Fock theory as particular cases, permits the computation of usual sets of connected diagrams while consistently incorporating static correlations through the highly non-perturbative restoration of rotational symmetry. Interestingly, the yrast spectroscopy of the system, i.e. the lowest energy associated with each angular momentum, is accessed within a single calculation. A key difficulty presently overcome relates to the necessity to handle generalized energy and norm kernels for which naturally terminating CC expansions could be eventually obtained. The present work focuses on SU(2) but can be extended to any (locally) compact Lie group and to discrete groups, such as most point groups. In particular, the formalism will be soon generalized to U(1) symmetry associated with particle number conservation. This is relevant to Bogoliubov CC theory that was recently applied to singly open-shell nuclei.