15 research outputs found
Accurate relativistic many-body calculations of van der Waals coefficients C_8 and C_10 for alkali-metal dimers
We consider long-range interactions between two alkali-metal atoms in their
respective ground states. We extend the previous relativistic many-body
calculations of C_6 dispersion coefficients [Phys.Rev. Lett. {\bf 82}, 3589
(1999)] to higher-multipole coefficients C_8 and C_10. A special attention is
paid to usually omitted contribution of core-excited states. We calculate this
contribution within relativistic random-phase approximation and demonstrate
that for heavy atoms core excitations contribute as much as 10% to the
dispersion coefficients. We tabulate results for both homonuclear and
heteronuclear dimers and estimate theoretical uncertainties. The estimated
uncertainties for C_8 coefficients range from 0.5% for Li_2 to 4% for Cs_2.Comment: 12 pages, submitted to Journal of Chemical Physic
Relativistic corrections to isotope shift in light ions
We calculate isotope mass shift for several light ions using Dirac wave
functions and mass shift operator with relativistic corrections of the order of
. Calculated relativistic corrections to the specific mass shift
vary from a fraction of a percent for Carbon, to 2% for Magnesium. Relativistic
corrections to the normal mass shift are typically smaller. Interestingly, the
final relativistic mass shifts for the levels of one multiplet appear to be
even closer than for non-relativistic operator. That can be important for the
astrophysical search for possible -variation, where isotope shift is a
source of important systematic error. Our calculations show that for levels of
the same multiplet this systematics is negligible and they can be used as
probes for -variation.Comment: 7 pages, 5 tables, revtex
Transition frequency shifts with fine structure constant variation for Fe II: Breit and core-valence correlation correction
Transition frequencies of Fe II ion are known to be very sensitive to
variation of the fine structure constant \alpha. The resonance absorption lines
of Fe II from objects at cosmological distances are used in a search for the
possible variation of \alpha in cause of cosmic time. In this paper we
calculated the dependence of the transition frequencies on \alpha^2 (q-factors)
for Fe II ion. We found corrections to these coefficients from valence-valence
and core-valence correlations and from the Breit interaction. Both the
core-valence correlation and Breit corrections to the q-factors appeared to be
larger than had been anticipated previously. Nevertheless our calculation
confirms that the Fe II absorption lines seen in quasar spectra have large
q-factors of both signs and thus the ion Fe II alone can be used in the search
for the \alpha-variation at different cosmological epochs.Comment: 7 pages, submitted to Phys. Rev.
Development of a configuration-interaction + all-order method for atomic calculations
We develop a theoretical method within the framework of relativistic
many-body theory to accurately treat correlation corrections in atoms with few
valence electrons. This method combines the all-order approach currently used
in precision calculations of properties of monovalent atoms with the
configuration-interaction approach that is applicable for many-electron
systems. The method is applied to Mg, Ca, Sr, Zn, Cd, Ba, and Hg to evaluate
ionization energies and low-lying energy levels.Comment: 10 page
Relativistic calculations of the K-K charge transfer and K-vacancy production probabilities in low-energy ion-atom collisions
The previously developed technique for evaluation of charge-transfer and
electron-excitation processes in low-energy heavy-ion collisions [I.I. Tupitsyn
et al., Phys. Rev. A 82, 042701(2010)] is extended to collisions of ions with
neutral atoms. The method employs the active electron approximation, in which
only the active electron participates in the charge transfer and excitation
processes while the passive electrons provide the screening DFT potential. The
time-dependent Dirac wave function of the active electron is represented as a
linear combination of atomic-like Dirac-Fock-Sturm orbitals, localized at the
ions (atoms). The screening DFT potential is calculated using the overlapping
densities of each ions (atoms), derived from the atomic orbitals of the passive
electrons. The atomic orbitals are generated by solving numerically the
one-center Dirac-Fock and Dirac-Fock-Sturm equations by means of a
finite-difference approach with the potential taken as the sum of the exact
reference ion (atom) Dirac-Fock potential and of the Coulomb potential from the
other ion within the monopole approximation. The method developed is used to
calculate the K-K charge transfer and K-vacancy production probabilties for the
Ne -- F collisions at the F projectile
energies 130 keV/u and 230 keV/u. The obtained results are compared with
experimental data and other theoretical calculations. The K-K charge transfer
and K-vacancy production probabilities are also calculated for the Xe --
Xe collision.Comment: 16 pages, 4 figure
High accuracy calculation of 6s -> 7s parity nonconserving amplitude in Cs
We calculated the parity nonconserving (PNC) 6s -> 7s amplitude in Cs. In the
Dirac-Coulomb approximation our result is in a good agreement with other
calculations. Breit corrections to the PNC amplitude and to the Stark-induced
amplitude are found to be -0.4% and -1% respectively. The weak charge
of Cs is in agreement with the standard model.Comment: 4 pages, LaTeX2e, uses revtex4.cls, submitted to PR