Surzhykov, A., J. P. Santos, P. Amaro, and P. Indelicato. "
Negative-continuum effects on the two-photon decay rates of hydrogenlike ions."
Physical Review A (Atomic, Molecular, and Optical Physics) 80 (2009): 052511.
AbstractTwo-photon decay of hydrogenlike ions is studied within the framework of second-order perturbation theory, based on the relativistic Dirac's equation. Special attention is paid to the effects arising from the summation over the negative-energy (intermediate virtual) states that occur in such a framework. In order to investigate the role of these states, detailed calculations have been carried out for the 2s1/2–>1s1/2 and 2p1/2–>1s1/2 transitions in neutral hydrogen H as well as for hydrogenlike xenon Xe53+ and uranium U91+ ions. We found that for a correct evaluation of the total and energy-differential decay rates, summation over the negative-energy part of Dirac's spectrum should be properly taken into account both for high-Z and low-Z atomic systems.
Morrison, J. C., S. Boyd, L. Marsano, B. Bialecki, T. Ericsson, and J. P. Santos. "
Numerical methods for solving the Hartree-Fock equations of diatomic molecules I."
Communications in Computational Physics 5 (2008): 959-985.
AbstractThe theory of domain decomposition is described and used to divide the variable domain of a diatomic molecule into separate regions which are solved independently. This approach makes it possible to use fast Krylov methods in the broad interior of the region while using explicit methods such as Gaussian elimination on the boundaries. As is demonstrated by solving a number of model problems, these methods enable one to obtain solutions of the relevant partial differential equations and eigenvalue equations accurate to six significant figures with a small amount of computational time. Since the numerical approach described in this article decomposes the variable space into separate regions where the equations are solved independently, our approach is very well-suited to parallel computing and offers the long term possibility of studying complex molecules by dividing them into smaller fragments that are calculated separately.
Martins, M. C., J. P. Marques, A. M. Costa, J. P. Santos, F. Parente, S. Schlesser, Le E. - O. Bigot, and P. Indelicato. "
Production and decay of sulfur excited species in an electron-cyclotron-resonance ion-source plasma."
Physical Review A (Atomic, Molecular, and Optical Physics) 80 (2009): 032501.
AbstractThe most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double-KL and triple-KLL ionizations, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multiconfiguration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kalpha x-ray spectrum is obtained, which is compared to recent experimental data.