Showing papers by "Ian P. Grant published in 2014"

Convergence of the Breit interaction in self-consistent and configuration-interaction approaches

Abstract: Much discussion in relativistic atomic physics and quantum optics has related to the interaction of gauge and perturbation of the Hamiltonian or Dirac operator. It has been commented that Lorentz and gauge independence requires different forms of the perturbation operator in shifting from one gauge to another. Equally, it has been commented that gauge convergence is not possible without different operator forms in different bases and without the operator being embedded within the self-consistent kernel. We explore the logic and self-consistency of these arguments, applied to the well-known Breit operator in an area of continuing discussion. We find that convergence is now possible to a remarkable degree including a Breit interaction operator in a form consistent with the gauge for length and velocity relativistic forms of the multipole operator, implemented at the configuration-interaction level. Excellent convergence is obtained for Breit interaction energies, interaction mixing coefficients, interaction transition probabilities and eigenenergies and transition probabilities in complex open shells (transition metal K $\ensuremath{\alpha}$ transitions and shake satellites), and forbidden transitions.

Advanced ab initio relativistic calculations of transition probabilities for some O i and O iii emission lines

Abstract: This work presents new ab initio relativistic calculations using the multiconfiguration Dirac-Hartree-Fock method of some O I and O III transition lines detected in B-type and Wolf-Rayet stars. Our results are the first able to be presented in both the length and velocity gauges, with excellent gauge convergence. Compared to previous experimental and theoretical uncertainties of up to 50 per cent, our accuracies appear to be in the range of 0.33-5.60 per cent, with gauge convergence up to 0.6 per cent. Similar impressive convergence of the calculated energies is also shown. Two sets of theoretical computations are compared with earlier tabulated measurements. Excellent agreement is obtained with one set of transitions but an interesting and consistent discrepancy exists between the current work and the prior literature, deserving of future experimental studies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.