Formulation and implementation of the relativistic Fock-space coupled cluster method for molecules

Visscher, Lucas; Eliav, Ephraim; Kaldor, Uzi

doi:10.1063/1.1415746

Cited by 238 publications

(167 citation statements)

References 47 publications

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“…A single-reference approach can be used since, in contrast to approaches in which SOC is added a posteriori; the determinants ͉5f 5/2 7s ±1/2 ͉ and ͉5f 5/2 5f 3/2 ͉ provide good first approximations to the 2 u , 3 u , and 4 g states. This method is complemented by the genuine multireference FSCC approach 57 in which we start from a common closed shell reference determinant of the UO 2 2+ molecule, or the U 6+ ion, then add two electrons successively in sectors ͑0,1͒ and ͑0,2͒. A full CI ͑P-space diagonalization͒ is performed in the selected Fock space valence sectors, in order to obtain the nondynamic correlation energy and the multireference wavefunction characteristics of each excited state.…”

Section: Methodsmentioning

confidence: 99%

A Fock space coupled cluster study on the electronic structure of the UO2, UO2+, U4+, and U5+ species

Infante

Eliav

Vilkas

et al. 2007

The Journal of Chemical Physics

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137

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The ground and excited states of the UO 2 molecule have been studied using a Dirac-Coulomb intermediate Hamiltonian Fock-space coupled cluster approach ͑DC-IHFSCC͒. 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 UO 2 + and UO 2 2+ as well as on the ions U 4+ and U 5+ 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 UO 2 molecule as a 3 ⌽ 2u state that arises from the 5f 1 7s 1 configuration. The first state from the 5f 2 configuration is found above 10 000 cm −1 , whereas the first state from the 5f 1 6d 1 configuration is found at 5 047 cm −1 .

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Section: Methodsmentioning

confidence: 99%

A Fock space coupled cluster study on the electronic structure of the UO2, UO2+, U4+, and U5+ species

Infante

Eliav

Vilkas

et al. 2007

The Journal of Chemical Physics

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137

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“…The molecular radical HgF, on the other hand, has a 2 R þ 1 2 ground state which in general calls for a multi-reference treatment. We therefore applied both the Fock-space coupled-cluster singles and doubles [63] (FS-CCSD) method, a genuine multi-reference CC method, and an open-shell CCSD(T) ansatz for the calculation of the ground state contact density. As the relative deviations in the electron densities between the two approaches was less than 10 ppm, we will in the following only refer to the open-shell CCSD(T) data.…”

Section: Electron Correlation Methodsmentioning

confidence: 99%

Mössbauer spectroscopy for heavy elements: a relativistic benchmark study of mercury

Knecht

Fux

Meer³

et al. 2011

Theor Chem Acc

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The electrostatic contribution to the Mössbauer isomer shift of mercury for the series HgF n (n = 1, 2, 4) with respect to the neutral atom has been investigated in the framework of four-and two-component relativistic theory. Replacing the integration of the electron density over the nuclear volume by the contact density (that is, the electron density at the nucleus) leads to a 10% overestimation of the isomer shift. The systematic nature of this error suggests that it can be incorporated into a correction factor, thus justifying the use of the contact density for the calculation of the Mössbauer isomer shift. The performance of a large selection of density functionals for the calculation of contact densities has been assessed by comparing with finite-field four-component relativistic coupled-cluster with single and double and perturbative triple excitations [CCSD(T)] calculations. For the absolute contact density of the mercury atom, the Density Functional Theory (DFT) calculations are in error by about 0.5%, a result that must be judged against the observation that the change in contact density along the series HgF n (n = 1, 2, 4), relevant for the isomer shift, is on the order of 50 ppm with respect to absolute densities. Contrary to previous studies of the 57 Fe isomer shift (F Neese, Inorg Chim Acta 332:181, 2002), for mercury, DFT is not able to reproduce the trends in the isomer shift provided by reference data, in our case CCSD(T) calculations, notably the non-monotonous decrease in the contact density along the series HgF n (n = 1, 2, 4). Projection analysis shows the expected reduction of the 6s 1/2 population at the mercury center with an increasing number of ligands, but also brings into light an opposing effect, namely the increasing polarization of the 6s 1/2 orbital due to increasing effective charge of the mercury atom, which explains the nonmonotonous behavior of the contact density along the series. The same analysis shows increasing covalent contributions to bonding along the series with the effective charge of the mercury atom reaching a maximum of around ?2 for HgF 4 at the DFT level, far from the formal charge ?4 suggested by the oxidation state of this recently observed species. Whereas the geometries for the linear HgF 2 and square-planar HgF 4 molecules were taken from previous computational studies, we optimized the equilibrium distance of HgF at the four-component Fock-space CCSD/aug-cc-pVQZ level, giving spectroscopic constants r e = 2.007 Å and x e = 513.5 cm -1 .Dedicated to Professor Pekka Pyykkö on the occasion of his 70th birthday and published as part of the Pyykkö Festschrift Issue.Electronic supplementary material The online version of this article

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“…16 The SbF and SbCl molecules are open-shell systems with triplet spin multiplicity. To deal with such systems we employed the Fock-space coupled cluster ͑FSCC͒ method 17 that starts with the definition of closed-shell reference systems ͑SbF +2 and SbCl +2 ͒ with a subsequent calculation of double electron affinities to end up with the SbF and SbCl results. The perturbative triple corrections were in this case taken from the closed-shell reference system, i.e., the effective Hamiltonian used to determined the correlated electron affinities was determined on basis of a CCSD wave operator.…”

Section: Computational Detailsmentioning

confidence: 99%

The nuclear electric quadrupole moment of antimony from the molecular method

Haiduke

Silva

Visscher

2006

The Journal of Chemical Physics

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Relativistic Dirac-Coulomb ͑DC͒ Hartree-Fock calculations are employed to obtain the analytic electric field gradient ͑EFG͒ on the antimony nucleus in the SbN, SbP, SbF, and SbCl molecules. The electronic correlation contribution to the EFGs is included with the DC-CCSD͑T͒ and DC-CCSD-T approaches, also in the four-component framework, using a finite-difference method. The total EFG results, along with the experimental nuclear quadrupole coupling constants from microwave spectroscopy, allow to derive the nuclear quadrupole moments of 121 Sb and 123 Sb, respectively, as −543͑11͒ and −692͑14͒ mb.

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Formulation and implementation of the relativistic Fock-space coupled cluster method for molecules

Cited by 238 publications

References 47 publications

A Fock space coupled cluster study on the electronic structure of the UO2, UO2+, U4+, and U5+ species

A Fock space coupled cluster study on the electronic structure of the UO2, UO2+, U4+, and U5+ species

Mössbauer spectroscopy for heavy elements: a relativistic benchmark study of mercury

The nuclear electric quadrupole moment of antimony from the molecular method

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