Topic
Coupled cluster
About: Coupled cluster is a research topic. Over the lifetime, 6280 publications have been published within this topic receiving 301055 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this paper, the static and frequency-dependent polarizabilities and first hyperpolarizabilities have been calculated for HF and Ne using full configuration interaction (FCI) and a hierarchy of coupled cluster models.
Abstract: Static and frequency-dependent polarizabilities and first hyperpolarizabilities have been calculated for HF and Ne using full configuration interaction (FCI) and a hierarchy of coupled cluster models: coupled cluster singles (CCS), an approximate coupled cluster singles and doubles model (CC2), coupled cluster singles and doubles (CCSD), an approximate coupled cluster singles, doubles, and triples model (CC3), and coupled cluster singles, doubles, and triples (CCSDT). A previous study of BH concerning FCI benchmarking has been extended to include CC3 and static CCSDT values. Systematic improvements of the polarizabilities and the hyperpolarizabilities are found going from CCS to CCSD and from CCSD to CC3 or CCSDT. Little or no improvement of the polarizabilities and no improvement of the hyperpolarizabilities are seen when going from CCS to CC2. The CCSD results represent a significant improvement over CCS and CC2 but are again surpassed by the CC3 results which agree very well with the FCI values. The re...
90 citations
TL;DR: In this paper, double-substitution amplitudes in the CCSD and MP1 wavefunctions are computed for predicting structures and harmonic vibrational frequencies for 34 molecules and the application of D1 and D2 to diradicals and bond dissociation.
90 citations
TL;DR: Complementary calculations confirm the assignment of the ground state of the UO(2) molecule as a (3)Phi(2u) state that arises from the 5f(1)7s( 1) configuration.
Abstract: The ground and excited states of the UO2 molecule have been studied using a Dirac-Coulomb intermediate Hamiltonian Fock-space coupled cluster approach (DC-IHFSCC). This method is unique in describing dynamic and nondynamic correlation energies at relatively low computational cost. Spin-orbit coupling effects have been fully included by utilizing the four-component Dirac-Coulomb Hamiltonian from the outset. Complementary calculations on the ionized systems UO2+ and UO22+ as well as on the ions U4+ and U5+ were performed to assess the accuracy of this method. The latter calculations improve upon previously published theoretical work. Our calculations confirm the assignment of the ground state of the UO2 molecule as a Φ2u3 state that arises from the 5f17s1 configuration. The first state from the 5f2 configuration is found above 10000cm−1, whereas the first state from the 5f16d1 configuration is found at 5047cm−1.
90 citations
TL;DR: It is demonstrated that for all choices of virtual orbitals much smaller domains are needed in the explicitly correlation methods than without the explicitly correlated terms, since the latter correct a large part of the domain error, as found previously.
Abstract: Explicitly correlated local coupled-cluster (LCCSD-F12) methods with pair natural orbitals (PNOs), orbital specific virtual orbitals (OSVs), and projected atomic orbitals (PAOs) are compared. In all cases pair-specific virtual subspaces (domains) are used, and the convergence of the correlation energy as a function of the domain sizes is studied. Furthermore, the performance of the methods for reaction energies of 52 reactions involving 58 small and medium sized molecules is investigated. It is demonstrated that for all choices of virtual orbitals much smaller domains are needed in the explicitly correlated methods than without the explicitly correlated terms, since the latter correct a large part of the domain error, as found previously. For PNO-LCCSD-F12 with VTZ-F12 basis sets on the average only 20 PNOs per pair are needed to obtain reaction energies with a root mean square deviation of less than 1 kJ mol−1 from complete basis set estimates. With OSVs or PAOs at least 4 times larger domains are needed for the same accuracy. A new hybrid method that combines the advantages of the OSV and PNO methods is proposed and tested. While in the current work the different local methods are only simulated using a conventional CCSD program, the implications for low-order scaling local implementations of the various methods are discussed.
90 citations
TL;DR: Ground- and excited-state energies, as well as ionization potentials and electron affinities, are calculated for all the alkali-metal atoms Li\char21{}Fr by the relativistic Fock-space coupled-cluster method.
Abstract: Ground- and excited-state energies, as well as ionization potentials and electron affinities, are calculated for all the alkali-metal atoms Li\char21{}Fr by the relativistic Fock-space coupled-cluster method. The coupled-cluster singles and doubles approximation, which includes single and double virtual excitations in a self-consistent manner, is implemented. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point. Rather extensive basis sets of balanced Gaussian spinors are used to span the atomic orbitals. The average error for the ionization potentials is 0.09% and for excitation energies 0.2%. Electron affinities are less accurate, particularly for the heavier atoms, with errors of 4\char21{}9 % for K, Rb, and Cs.
90 citations