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Moser, I., F. Mota-Furtado, P. F. O'Mahony, and J. P. Santos. "Rydberg wave packets in parallel electric and magnetic fields." Physical Review A 55 (1997): 3724-3729. Abstract

The magnitude of the time autocorrelation function M between states excited by two Gaussian laser pulses is calculated for both hydrogen and rubidium atoms inparallel electric and magnetic fields. M is determined by a full quantum-mechanical calculation but the peaks are identified with the periods of the shortest periodicorbits of the corresponding classical system. Qualitative agreement is obtained with experimental results, however, discrepancies are found in the relative heights ofthe peaks.

Santos, J. P., F. Mota-Furtado, M. F. Laranjeira, and F. Parente. "Rydberg states of atoms in parallel electric and magnetic fields." Physical Review A 59 (1999): 1703-1706. AbstractWebsite

We present theoretical results for the photoabsorption spectrum of an atom in parallel electric and magnetic fields, using the R-matrix method combined with quantum-defect theory. We introduce a radial basis set which is complete and orthonormal over a semi-infinite interval [r0,(infinity)), to allow calculations to be performed for high Rydberg states in nonhydrogenic atoms without encountering problems due to linear dependence of the basis set. The nonhydrogenic character of the spectra is analyzed for Li and Rb, and a comparison is made with previous high-precision experiments which shows that the theoretical results agree very well with experiment.

Santos, J. P., Chintan Shah, José Crespo R. López-Urrutia, Ming Feng Gu, Thomas Pfeifer, José Marques, Filipe Grilo, José Paulo Santos, and Pedro Amaro. "Revisiting the Fe xvii Line Emission Problem: Laboratory Measurements of the 3s–2p and 3d–2p Line-formation Channels." The Astrophysical Journal (2019). AbstractWebsite
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Amaro, P., J. P. Santos, F. Parente, A. Surzhykov, and P. Indelicato. "Resonance effects on the two-photon emission from hydrogenic ions." Physical Review A (Atomic, Molecular, and Optical Physics) 79 (2009): 062504. AbstractWebsite
A theoretical study of the all two-photon transitions from initial bound states with ni=2,3 in hydrogenic ions is presented. High-precision values of relativistic decay rates for ions with nuclear charge in the range 1<=Z<=92 are obtained through the use of finite basis sets for the Dirac equation constructed from B splines. We also report the spectral (energy) distributions of several resonant transitions, which exhibit interesting structures, such as zeros in the emission spectrum, indicating that two-photon emission is strongly suppressed at certain frequencies. We compare two different approaches (the line profile approach and the QED approach based on the analysis of the relativistic two-loop self-energy) to regularize the resonant contribution to the decay rate. Predictions for the pure two-photon contributions obtained in these approaches are found to be in good numerical agreement.
Amaro, P., J. P. Santos, F. Parente, A. Surzhykov, and P. Indelicato. "Resonance effects on the two-photon emission from hydrogenic ions." Physical Review A 79 (2009): 062504. AbstractWebsite

A theoretical study of the all two-photon transitions from initial bound states with ni=2,3 in hydrogenic ions is presented. High-precision values of relativistic decay rates for ions with nuclear charge in the range 1<=Z<=92 are obtained through the use of finite basis sets for the Dirac equation constructed from B splines. We also report the spectral (energy) distributions of several resonant transitions, which exhibit interesting structures, such as zeros in the emission spectrum, indicating that two-photon emission is strongly suppressed at certain frequencies. We compare two different approaches (the line profile approach and the QED approach based on the analysis of the relativistic two-loop self-energy) to regularize the resonant contribution to the decay rate. Predictions for the pure two-photon contributions obtained in these approaches are found to be in good numerical agreement.

Santos, J., A. Costa, C. Madruga, F. Parente, and P. Indelicato. "Relativistic transition wavelenghts and probabilities for spectral lines of Ne II." The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics 63 (2011): 89-96. AbstractWebsite

Transition wavelengths and probabilities for several 2 p 4 3 p -2 p 4 3 s and 2 p 4 3 d -2 p 4 3 p lines in fluorine-like neon ion (NeII) have been calculated within the multiconfiguration Dirac-Fock (MCDF) method with quantum electrodynamics (QED) corrections. The results are compared with all existing experimental and theoretical data.

Santos, J. P., A. Costa, C. Madruga, F. Parente, and P. Indelicato. "Relativistic transition wavelenghts and probabilities for spectral lines of Ne II." The European Physical Journal D 63 (2011): 89-96. AbstractWebsite

Transition wavelengths and probabilities for several 2 p 4 3 p -2 p 4 3 s and 2 p 4 3 d -2 p 4 3 p lines in fluorine-like neon ion (NeII) have been calculated within the multiconfiguration Dirac-Fock (MCDF) method with quantum electrodynamics (QED) corrections. The results are compared with all existing experimental and theoretical data.

Santos, J. P., C. Madruga, F. Parente, and P. Indelicato. "Relativistic transition probabilities for F-like ions with 10⩽Z⩽49." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 235 (2005): 171-173. AbstractWebsite

In the present work we have calculated several relativistic transition probabilities for the F-like ions with 10 less-than-or-equals, slant Z less-than-or-equals, slant 49, in the framework of the Multi-Configuration Dirac–Fock method, for applications on laserphysics and astrophysics. The lines considered correspond to transitions between levels of 2p43s, 2p43p and 2p43d configurations. The spectral fine structure is taken into consideration and the results for individual lines are given.

"Relativistic transition probabilities for F-like ions with 10." Nuclear Instruments and Methods in Physics Research Section B 235 (2005): 171. AbstractWebsite
In the present work we have calculated several relativistic transition probabilities for the F-like ions with 10 less-than-or-equals, slant Z less-than-or-equals, slant 49, in the framework of the Multi-Configuration Dirac–Fock method, for applications on laserphysics and astrophysics. The lines considered correspond to transitions between levels of 2p43s, 2p43p and 2p43d configurations. The spectral fine structure is taken into consideration and the results for individual lines are given.
Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, and F. Fratini. "Relativistic total cross section and angular distribution for Rayleigh scattering by atomic hydrogen." Phys. Rev. A 85 (2012): 043406. AbstractWebsite

We study the total cross section and angular distribution in Rayleigh scattering by hydrogen atom in the ground state, within the framework of Dirac relativistic equation and second-order perturbation theory. The relativistic states used for the calculations are obtained by making use of the finite basis-set method and expressed in terms of B splines and B polynomials. We pay particular attention to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction. It is shown that the angular distribution of scattered photons, while symmetric with respect to the scattering angle θ=90∘ within the electric dipole approximation, becomes asymmetric when higher multipoles are taken into account. The analytical expression of the angular distribution is parametrized in terms of Legendre polynomials. Detailed calculations are performed for photons in the energy range 0.5 to 10 keV. When possible, results are compared with previous calculations.

Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, and F. Fratini. "Relativistic total cross section and angular distribution for Rayleigh scattering by atomic hydrogen." Physical Review A 85 (2012): 043406. AbstractWebsite

We study the total cross section and angular distribution in Rayleigh scattering by hydrogen atom in the ground state, within the framework of Dirac relativistic equation and second-order perturbation theory. The relativistic states used for the calculations are obtained by making use of the finite basis-set method and expressed in terms of B splines and B polynomials. We pay particular attention to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction. It is shown that the angular distribution of scattered photons, while symmetric with respect to the scattering angle θ=90∘ within the electric dipole approximation, becomes asymmetric when higher multipoles are taken into account. The analytical expression of the angular distribution is parametrized in terms of Legendre polynomials. Detailed calculations are performed for photons in the energy range 0.5 to 10 keV. When possible, results are compared with previous calculations.

Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, S. Tashenov, and F. Fratini. "Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen." Phys. Rev. A 86 (2012): 043405. AbstractWebsite

A relativistic analysis of the polarization properties of light elastically scattered by atomic hydrogen is performed, based on the Dirac equation and second-order perturbation theory. The relativistic atomic states used for the calculations are obtained by making use of the finite basis set method and are expressed in terms of B splines and B polynomials. We introduce two experimental scenarios in which the light is circularly and linearly polarized, respectively. For each of these scenarios, the polarization-dependent angular distribution and the degrees of circular and linear polarization of the scattered light are investigated as a function of scattering angle and photon energy. Analytical expressions are derived for the polarization-dependent angular distribution which can be used for scattering by both hydrogenic as well as many-electron systems. Detailed computations are performed for Rayleigh scattering by atomic hydrogen within the incident photon energy range 0.5 to 5 keV. Particular attention is paid to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction.

Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, S. Tashenov, and F. Fratini. "Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen." Physical Review A 86 (2012): 043405. AbstractWebsite

A relativistic analysis of the polarization properties of light elastically scattered by atomic hydrogen is performed, based on the Dirac equation and second-order perturbation theory. The relativistic atomic states used for the calculations are obtained by making use of the finite basis set method and are expressed in terms of B splines and B polynomials. We introduce two experimental scenarios in which the light is circularly and linearly polarized, respectively. For each of these scenarios, the polarization-dependent angular distribution and the degrees of circular and linear polarization of the scattered light are investigated as a function of scattering angle and photon energy. Analytical expressions are derived for the polarization-dependent angular distribution which can be used for scattering by both hydrogenic as well as many-electron systems. Detailed computations are performed for Rayleigh scattering by atomic hydrogen within the incident photon energy range 0.5 to 5 keV. Particular attention is paid to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction.

Amaro, Pedro, Filippo Fratini, Laleh Safari, Jorge Machado, Mauro Guerra, Paul Indelicato, and Jose Paulo Santos. "Relativistic evaluation of the two-photon decay of the metastable 1s22s2p 3P0 state in berylliumlike ions with an effective-potential model." Physical Review A 93 (2016): 032502-8. AbstractWebsite

The two-photon $1{s}^{2}2s2p\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{0}\ensuremath{\rightarrow}1{s}^{2}{s}^{2}\phantom{\rule{0.16em}{0ex}}{}^{1}{S}_{0}$ transition in berylliumlike ions is investigated theoretically within a fully relativistic framework and a second-order perturbation theory. We focus our analysis on how electron correlation, as well as the negative-energy spectrum, can affect the forbidden $E1M1$ decay rate. For this purpose, we include the electronic correlation via an effective local potential and within a single-configuration-state model. Due to its experimental interest, evaluations of decay rates are performed for berylliumlike xenon and uranium. We find that the negative-energy contribution can be neglected at the present level of accuracy in the evaluation of the decay rate. On the other hand, if contributions of electronic correlation are not carefully taken into account, it may change the lifetime of the metastable state by up to 20%. By performing a fully relativistic $jj$-coupling calculation, we find a decrease of the decay rate by two orders of magnitude compared to nonrelativistic $LS$-coupling calculations, for the selected heavy ions.

Santos, J. P., G. C. Rodrigues, J. P. Marques, F. Parente, J. P. Desclaux, and P. Indelicato. "Relativistic correlation correction to the binding energies of the ground configuration of beryllium-like, neon-like, magnesium-like and argon-like ions." The European Physical Journal D 37 (2006): 201-207. AbstractWebsite
Total electronic correlation corrections to the binding energies of the isoelectronic series of beryllium, neon, magnesium and argon, are calculated in the framework of relativistic multiconfiguration Dirac-Fock method. Convergence of the correlation energies is studied as the active set of orbitals is increased. The Breit interaction is treated fully self-consistently. The final results can be used in the accurately determination of atomic masses from highly charged ions data obtained in Penning-trap experiments.
Santos, J. P., G. C. Rodrigues, J. P. Marques, F. Parente, J. P. Desclaux, and P. Indelicato. "Relativistic correlation correction to the binding energies of the ground configuration of beryllium-like, neon-like, magnesium-like and argon-like ions." The European Physical Journal D 37 (2006): 201-207. AbstractWebsite

Total electronic correlation corrections to the binding energies of the isoelectronic series of beryllium, neon, magnesium and argon, are calculated in the framework of relativistic multiconfiguration Dirac-Fock method. Convergence of the correlation energies is studied as the active set of orbitals is increased. The Breit interaction is treated fully self-consistently. The final results can be used in the accurately determination of atomic masses from highly charged ions data obtained in Penning-trap experiments.

Guerra, M., P. Amaro, J. P. Santos, and P. Indelicato. "Relativistic calculations of screening parameters and atomic radii of neutral atoms." Atomic Data and Nuclear Data Tables 117-118 (2017): 439-457. AbstractWebsite

Atomic Data and Nuclear Data Tables, 117-118 (2017) 439-457. doi:10.1016/j.adt.2017.01.001

Sampaio, J. M., T. I. Madeira, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of M-shell photoionization and X-ray production cross-sections for Hg at 5.96 keV excitation energy." Radiation Physics and Chemistry 107 (2014): 36. AbstractWebsite

In this work we calculate photoionization and X-ray production cross-sections (XPCS) of M-shell vacancies in Hg at incident photon energy of 5.96 keV (low.

Sampaio, J. M., T. I. Madeira, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of M-shell photoionization and X-ray production cross-sections for Hg at 5.96 keV excitation energy." Radiation Physics and Chemistry 107 (2015): 36. AbstractWebsite

In this work we calculate photoionization and X-ray production cross-sections (XPCS) of M-shell vacancies in Hg at incident photon energy of 5.96 keV (low.

Sampaio, J. M., T. I. Madeira, M. Guerra, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of K-, L- and M-shell X-ray production cross-sections by electron impact for Ne, Ar, Kr, Xe, Rn and Uuo." Journal of Quantitative Spectroscopy and Radiative Transfer 182 (2016): 87-93. AbstractWebsite

Journal of Quantitative Spectroscopy and Radiative Transfer, 182 + (2016) 87-93. doi:10.1016/j.jqsrt.2016.05.012

Sampaio, J. M., M. Guerra, T. I. Madeira, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of atomic parameters in Ununoctium." Journal of Physics: Conference Series 635 (2015): 092095-2. AbstractWebsite
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Indelicato, P., E. Lindroth, T. Beier, J. Bieron, A. M. Costa, I. Lindgren, J. P. Marques, A. M. Martenson-Pendrill, M. C. Martins, M. A. Ourdane, F. Parente, P. Patté, G. C. Rodrigues, S. Salomonson, and J. P. Santos. "Relativistic Calculations for Trapped Ions." Hyperfine Interactions 132 (2001): 347-361. AbstractWebsite

We present recent results in the field of total binding energy calculations, Land&shchcy; factors, quantum electrodynamics corrections and lifetime that are of interest for ion traps and ion sources. We describe in detail MCDF and RMBPT calculation of ionic binding energies, which are needed for the determination of atomic masses from highly charged ion measurements. We also show new results concerning Land&shchcy; factor in 3-electron ions. Finally we describe how relativistic calculations can help understand the physics of heavy ion production ion sources.

Martins, M. C., A. M. Costa, J. P. Santos, F. Parente, and P. Indelicato. "Relativistic calculation of two-electron one-photon and hypersatellite transition energies for 12<=Z<=30 elements." Journal of Physics B: Atomic and Molecular Physics 37 (2004): 3785-3795. AbstractWebsite

Energies of two-electron one-photon transitions from initial double K-hole states were computed using the Dirac–Fock model. The transition energies of competing processes, the Ka hypersatellites, were also computed. The results are compared with experiment and to other theoretical calculations.

Costa, A. M., M. C. Martins, J. P. Santos, P. Indelicato, and F. Parente. "Relativistic calculation of Kβ hypersatellite energies and transition probabilities for selected atoms with 13<=Z<=80." Journal of Physics B: Atomic and Molecular Physics 39 (2006): 2355-2366. AbstractWebsite
Energies and transition probabilities of Kβ hypersatellite lines are computed using the Dirac–Fock model for several values of Z throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the Kβh1/Kβh3 intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.