arXiv subjects

B. P. Das

Publications and source records attributed to B. P. Das.

102 records · Page 6Linked to original sources

arXiv2005

Relativistic Coupled-Cluster Theory of Atomic Parity Nonconservation: Application to $^{137}$Ba$^+$

We report the result of our {\it ab initio} calculation of the $6s ^2S_{1/2} \to 5d ^2D_{3/2}$ parity nonconserving electric dipole transition amplitude in $^{137}\text{Ba}^+$ based on relativistic coupled-cluster theory. Considering single, double and partial triple excitations, we have achieved an accuracy of less than one percent. If the accuracy of our calculation can be matched by the proposed parity nonconservation experiment in Ba$^+$ for the above transition,then the combination of the two results would provide an independent non accelerator test of the Standard Model of particle physics.

physics.atom-ph↗

arXiv2005

A New Limit for the Coupling Constant of the Electron-Nucleus Scalar-Pseudoscalar Interaction

We report the results of our calculations of the atomic electric dipole moments of cesium and thallium arising from the electron-nucleus scalar-pseudoscalar interaction. The calculations are based on the all order relativistic coupled-cluster theory. Electron correlation effects, particularly in the case of thallium are of crucial importance. We obtain a new limit for the scalar-pseudoscalar interaction by combining the result of our thallium calculation and the measured value of the electric dipole moment of that atom.

physics.atom-ph↗

arXiv2005

Nuclear Structure corrections for Parity Non-conservation in Atomic Ba$^+$ and Ra$^+$

We calculate the binding energy, charge radii in $^{126}$Ba--$^{140}$Ba and $^{214}$Ra--$^{228}$Ra using the relativistic mean field theory which includes scalar and vector mesons. We then evaluate the nuclear structure corrections to the weak charges for a series of isotopes of these atoms using different parameters and estimate their uncertainty in the framework of this model. Our results will have important implication for the ongoing and planned parity non-conservation experiments and atomic structure calculations on Ba$^+$ and Ra$^+$.

physics.atom-ph↗

arXiv2005

Electric quadrupole moment of the $4d ^{2}D_{5/2}$ state in $^{88}Sr^{+}$ and its role in an optical frequency standard

The electric quadrupole moment for the $4d ^2D_{5/2}$ state of $\mathrm{^{88}Sr^+}$, one of the most important candidates for an optical clock, has been calculated using the relativistic coupled-cluster theory. The result of the calculation is presented and the important many-body contributions are highlighted. The calculated electric quadrupole moment is $(2.94\pm0.07)ea_{0}^{2}$, where $a_{0}$ is the Bohr radius and $e$ the electronic charge while the measured value is $(2.6\pm0.3)ea_{0}^{2}$. This is so far the most accurate determination of the electric quadrupole moment for the above mentioned state.

physics.atom-ph↗

arXiv2005

Relativistic and correlation effects in atoms

This review article deals with some case studies of relativistic and correlation effects in atomic systems. After a brief introduction to relativistic many-electron theory, a number of applications ranging from correlation energy to parity non-conservation in atoms are considered. There is a special emphasis on relativistic coupled-cluster theory as most of the results presented here are based on it.

physics.atom-ph↗

arXiv2005

Case studies of atomic properties using coupled-cluster and unitary coupled-cluster methods

The magnetic dipole and electric quadrupole hyperfine constants of Aluminium ($^{27}Al$) atom are computed using the relativistic coupled cluster (CC) and unitary coupled cluster (UCC) methods. Effects of electron correlations are investigated using different levels of CC approximations and truncation schemes. The ionization potentials, excitation energies, transition probabilities, oscillator strengths and nuclear quadrupole moment are computed to assess the accuracy of these schemes. The nuclear quadrupole moment obtained from the present CC and UCC calculations in the singles and doubles approximations are 142.5 mbarn and 141.5 mbarn respectively. The discrepancies between our calculated IPs and EEs and their measured values are better than 0.3%. The other one-electron properties reported here are also in excellent agreement with the measurements.

physics.atom-ph↗

arXiv2005

Electron Correlation Effects in Hyperfine Interactions in $^{45}$Sc and $^{89}$Y

The relativistic coupled-cluster theory has been employed to calculate the magnetic dipole and electric quadrupole hyperfine structure constants for the stable isotopes $^{45}$Sc and $^{89}$Y. The role of electron correlation is found to be very important. The trend exhibited by these effects is rather different from previously studied single valence atomic systems.

physics.atom-ph↗

arXiv2005

Relativistic unitary coupled cluster theory and applications

We present the first formulation and application of relativistic unitary coupled cluster theory to atomic properties. The remarkable features of this theory are highlighted, and it is used to calculate the lifetimes of $5^{2}D_{3/2}$ and $6^{2}P_{3/2}$ states of $Ba^{+}$ and $Pb^{+}$ respectively. The results clearly suggest that it is very well suited for accurate \emph{ab initio} calculations of properties of heavy atomic systems.

physics.atom-ph↗

arXiv2004

Comparative studies of the magnetic dipole and electric quadrupole hyperfine constants for the ground and low lying excited states of ^{25}Mg^{+}

We have employed the relativistic coupled cluster theory to calculate the magnetic dipole and electric quadrupole hyperfine constants for the ground and low lying excited states of singly ionized magnesium. Comparison with experimental and the other theoretical results are done and predictions are also made for a few low lying excited states which could be of interest. We have made comparative studies of the important many body effects contributing to the hyperfine constants for the different states of the ion.

physics.atom-ph↗

arXiv2004

Application of Relativistic Coupled-cluster Theory to Heavy Atomic Systems with Strongly Interacting Configurations: Hyperfine Interactions in $^{207}Pb^+$

This work presents a first time accurate calculation of the magnetic dipole hyperfine structure constants for the ground state and some low-lying excited states of Pb$^+$. By comparing different levels of approximation with experimental results, we demonstrate the importance of correlation effects which reach beyond lower order relativistic many body perturbation theory. Employing relativistic coupled-cluster theory we obtain a quantitative understanding of the core-polarization and correlation effects inherent in this system and observe completely different trends compared to $Ba^+$.

physics.atom-ph↗

arXiv2004

Ab initio determination of the lifetime of the $6^2P_{3/2}$ state f or $^{207}Pb^+$ by relativistic many-body theory

Relativistic coupled-cluster(RCC) theory has been employed to calculate the life time of the $6 ^2P_{3/2}$ state of single ionized lead($^{207}Pb$) to an accurac y of 3% and compared with the corresponding value obtained using second order r elativistic many-body perturbation theory(RMBPT). This is one of the very few ap plications of this theory to excited state properties of heavy atomic systems. C ontributions from the different electron correlation effects are given explicitl y.

physics.atom-ph↗

arXiv1998

A New Approach To Relativistic Gaussian Basis Functions: Theory And Applications

We present a new hybrid method to solve the relativistic Hartree-Fock-Roothan equations where the one- and two-electron radial integrals are evaluated numerically by defining the basis functions on a grid. This procedure reduces the computational costs in the evaluation of two-electron radial integrals. The orbitals generated by this method are employed to compute the ionization potentials, excitation energies and oscillator strengths of alkali-metal atoms and elements of group IIIA through second order many-body perturbation theor and other correlated theories.

physics.atom-ph↗