High-accuracy calculation of nuclear quadrupole moments of atomic halogens

Abstract

We have investigated the functional derivative of the nonadditive kinetic-energy bifunctional, which appears in the embedding potential that is used in the frozen-density embedding formalism, in the limit that the separation of the subsystems is large. We have derived an exact expression for this kinetic-energy component of the embedding potential and have applied this expression to deduce its exact form in this limit. Comparing to the approximations currently in use, we find that while these approximations are correct at the nonfrozen subsystem, they fail completely at the frozen subsystem. Using test calculations on two model systems, a H 2 O¯Li + complex and a cluster of aminocoumarin C151 surrounded by 30 water molecules, we show that this failure leads to a wrong description of unoccupied orbitals, which can lead to convergence problems caused by too low-lying unoccupied orbitals and which can further have serious consequences for the calculation of response properties. Based on our results, a simple correction is proposed, and we show that this correction is able to fix the observed problems for the model systems studied.

Year-2008 nuclear quadrupole moments

“…The previous 'atomic þ molecular' Qð 79 Br) value of 313(3) mb [16] appeared after [2]. It is reasonably close to the new 'atomic' value of 302(5) mb by Yakobi et al [43] and is kept so far.…”

“…Although the two values are within each other's error limits, we now choose the latter as the new standard value. The new atomic value of Yakobi et al[43] would be À680ð10Þ mb, further down. The ratio between the excited-state and ground-state quadrupole moments has been measured as Q Ã =Q ¼ 0:896ð2Þ[84].…”

Fock-space multireference coupled-cluster calculations of the hyperfine structure of isoelectronic33S−and35,Das1, Chaudhuri2, Chattopadhyay3 et al. 2011Phys. Rev. A120120View full textAdd to dashboardCite

“…The study of hyperfine interactions for these systems is particularly important as the experimental [10][11][12] and theoretical studies (at ab-initio level) are scarce [9,[13][14][15][16][17]. The first ab initio study on the NQM of 35,37 Cl and 33 S (on S − ) was carried out by Sundholm and Olsen [13,18].…”

“…In their calculation, the electron correlation contribution has been accounted for at the level of the coupled-cluster method with singles, doubles, and perturbative triples [CCSD(T)] approximation and the spin-averaged no-pair approximation to the Dirac-Coulomb Hamiltonian has been used for the evaluation of the relativistic contribution. A full-blown relativistic MRCC calculation on the NQM of 35 Cl was later carried out by Yakobi et al [16]. They used the relativistic FS MRCC method to calculate the EFG at the atomic nuclei by the finite-field approach.…”

Polarization of core orbitals and computation of nuclear quadrupole coupling constants using Gaussian basis sets

“…In principle, such polarization is automatically included in ab initio and density functional calculations, with the EFG computed as a sum of contributions from the nuclear point charges and the electron density, usually evaluated 9 as the first derivative of the energy with respect to the nuclear quadrupole moment at Q = 0. In principle, for a complete basis set, this calculation should be exact at any level of electron correlation obeying the Hellmann-Feynman theorem.…”