B. P. Das

Relativistic Coupled Cluster (RCC) Computation of the Electric Dipole Moment Enhancement Factor of Francium Due to the Violation of Time Reversal Symmetry

A relativistic many-body theory for the electric dipole moment (EDM) of paramagnetic atoms arising from the electric dipole moment of the electron is presented and implemented. The relativistic coupled-cluster method with single and double excitations (RCCSD) using the Dirac-Coulomb Hamiltonian and a weak parity and time reversal violating interaction to the first-order of perturbation has been employed to obtain the EDM enhancement factor for the ground state of the Fr atom due to the intrinsic EDM of the electron. The trends of different correlation effects and the leading contributions from different physical states are discussed. Our results in combination with that of the Fr EDM experiment that is currently in progress possess the potential to probe the validity of the standard model (SM) of elementary particle physics.

Investigations of Ra(+) properties to test possibilities for new optical-frequency standards

The present work tests the suitability of the narrow transitions 7s (2)S(1/2)-> 6d (2)D(3/2) and 7s (2)S(1/2)-> 6d (2)D(5/2) in Ra(+) for optical frequency standard studies. Our calculations of the lifetimes of the metastable 6d states using the relativistic coupled-cluster theory suggest that they are sufficiently long for Ra(+) to be considered as a potential candidate for an atomic clock. This is further corroborated by our studies of the hyperfine interactions, dipole and quadrupole polarizabilities, and quadrupole moments of the appropriate states of this system.

Three-body on-site interactions in ultracold bosonic atoms in optical lattices and superlattices

The Mott insulator-superfluid transition for ultracold bosonic atoms in an optical lattice has been extensively studied in the framework of the Bose-Hubbard model with two-body on-site interactions. In this paper, we analyze the additional effect of the three-body on-site interactions on this phase transition in an optical lattice and the transitions between the various phases that arise in an optical superlattice. Using the mean-field theory and the density matrix renormalization group method, we find the phase diagrams depicting the relationships between various physical quantities in an optical lattice and superlattice. We also propose a possible experimental signature to observe the on-site three-body interactions.

Ab initio determination of polarizabilities and van der Waals coefficients of Li atoms using the relativistic coupled-cluster method

We report on a technique to determine the van der Waals coefficients of lithium (Li) atoms based on relativistic coupled-cluster theory. These quantities are determined using the imaginary parts of the scalar dipole and quadrupole polarizabilities, which are evaluated using an approach that we have proposed earlier [B. K. Sahoo, Chem. Phys. Lett. 448, 144 (2007)]. Our procedure is fully ab initio, and avoids the sum-over-the-states approach. We present the dipole and quadrupole polarizabilities of many of the low-lying excited states of Li. Also, the off-diagonal dipole and quadrupole polarizabilites between some of the low-lying states of Li have been calculated.

Relativistic coupled-cluster studies of ionization potentials, lifetimes and polarizabilities in singly ionized calcium

Using the relativistic coupled-cluster method, we have calculated ionization potentials, electric dipole transition amplitudes, and dipole polarizabilities of many low-lying states of Ca(+). Contributions from the Breit interaction are given explicitly for these properties. Polarizabilities of the ground and the first excited d states are determined by evaluating the wave functions that are perturbed to first order by the electric dipole operator and the black-body radiation shifts are estimated from these results. We also report the results of branching ratios and lifetimes of the first excited p states using both the calculated and experimental wavelengths and compare them with their measured values.

Comparative studies of dipole polarizabilities in Sr + , Ba + and Ra + and their applications to optical clocks

Static dipole polarizabilities are calculated in the ground and metastable states of Sr{sup +}, Ba{sup +} and Ra{sup +} using the relativistic coupled-cluster method. Trends of the electron correlation effects are investigated in these atomic ions. We also estimate the Stark and black-body radiation shifts from these results for these systems for the transitions proposed for the optical frequency standards and compare them with available experimental data.

Relativistic equation-of-motion coupled-cluster method for the double-ionization potentials of closed-shell atoms

We report the general implementation of the relativistic equation-of-motion coupled-cluster method to calculate double ionization spectra (DI-EOMCC) of atomic and molecular systems. As a first application, this method is employed to calculate the principal valence double ionization potential values of He and alkaline earth metal (Be, Mg, Ca, Sr and Ba) atoms. Our results are compared with the results available from the national institute of standards and technology (NIST) database and other ab initio calculations. We have achieved an accuracy of ~ 0.1%, which is an improvement over the first principles T-matrix calculations [J. Chem. Phys. 123, 144112 (2005)]. We also present results using the second-order many-body perturbation theory and the random- phase approximation in the equation-of-motion framework and these results are compared with the DI-EOMCC results.

Relativistic equation-of-motion coupled-cluster method: Application to closed-shell atomic systems

We report our successful implementation of the relativistic equation-of-motion coupled-cluster (EOMCC) method. This method is employed to compute the principal ionization potentials (IPs) of closed-shell rare-gas atoms, He-like ions, Be-like ions, along with Na

Correlation trends in the ground-state static electric dipole polarizabilities of closed-shell atoms and ions

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Theoretical studies of the atomic transitions in boron-like ions: Mg VIII, Si X and S XII

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