Molecular relativistic electric field gradient calculations suggest revision of the value of the nuclear electric quadrupole moment of 127I

Abstract

Relativistic ab initio methods are used to compute the electric field gradient at the iodine nucleus in nine different closed-shell diatomic molecules. Combining these theoretical electric field gradients with experimental nuclear quadrupole coupling constants gives a consistent value of the nuclear quadrupole moment of Iz7I of -696(12)millibarn. We argue that this value is more precise than the current standard value of the nuclear quadrupole moment of Iz7I and recommend adjusting the reference value accordingly. The precision of this determination is still determined by technical limitations in the theoretical work, in particular the neglect of the two-electron Gaunt interaction in the Hamiltonian and correlation contributions beyond those described at the CCSD(T) level of theory, but the errors are reduced relative to the theoretical work that underlies the current standard value of this nuclear quadrupole moment. As a secondary study we also considered the calculation of the small electric field gradient at the gold nucleus in the AuI molecule and conclude that this computation remains a challenge for theoreticians.

First principles calculation of Mössbauer isomer shift

“…In this respect, development of the first principles approaches, which go beyond the traditional perturbational treatment of isomer shift and incorporate inherently the aforementioned effects of relativity and electron correlation, should lead to a substantial progress towards a more accurate theoretical interpretation of Mössbauer spectra. In combination with the high-level computational approaches to the calculation of other nuclear parameters, such as quadrupole splitting [140][141][142][143][144][145][146][147][148][149] and hyperfine splitting constants [150][151][152], these developments will ultimately lead to a full theoretical characterization of Mössbauer spectra and to deeper understanding of their relationship with the electronic structure of materials.…”

The nuclear electric quadrupole moment of antimony from the molecular method

“…threshold ͑less than 0.1%͒ was reached. The Gaunt ͑G͒ integrals, not considered here, may probably introduce an error of less than 0.2% for antimony, under comparison with EFG results for other atoms with similar number of electrons 5 and as estimated by The EFG values could bot be calculated with DIRAC 04.1.…”

“…The derivation of NQMs for heavy atoms by the molecular method is still a challenge since the accuracy of EFG calculations in such systems requires accurate treatment for both relativistic and electronic correlation contributions. 4,5 One of the most precise ways of dealing with relativistic effects is given by the four-component Dirac-Coulomb ͑DC͒ approach. The electronic correlation, except in systems with uncommon electronic structures, can be well described with a coupled cluster method in which a cluster operator containing only single and double excitations ͑CCSD͒ is corrected for triple contributions in a noniterative way, either using the CCSD͑T͒ ͑Ref.…”

“…As a good description of the core region is essential in EFG calculations, a number of additional tight functions needs to be added to standard sets to reach the required accuracy in the computed EFG values. 4,5 In this work, the chosen antimony basis set is the relativistic adapted Gaussian basis set ͑RAGBS͒ ͑Ref. 8͒ that presents an error of only 1 mhartree with respect to the numerical reference values and is designed to furnish a precise description of the innermost region.…”

Desenvolvimento de conjuntos polarizados de funções de base relativísticas Gaussianas e aplicações

“…na qual ν X (v) é o valor disponível do NQCC para v = 0 e ν X,1 é dado pela aplicação do NQM calculado para a molécula de BiN em conjunto com um valor de q X,1 obtido a partir da primeira e segunda derivadas deste EFG em função de variações da distância de equilíbrio (ξ = (r − r e )/r e ) [97]:…”