arXiv subjects

Rajat K. Chaudhuri

Publications and source records attributed to Rajat K. Chaudhuri.

10 recordsLinked to original sources

arXiv2007

Core polarization in coupled-cluster theory induced by a parity and time-reversal violating interaction

The effects of parity and time reversal violating potential, in particular the tensor-pseudotensor electron nucleus interaction are studied. We establish that selected terms representing the interplay of these effects and the residual Coulomb interaction in the coupled-cluster method are equivalent to the coupled perturbed Hartree-Fock. We have shown that the {\em normal} CPHF diagrams have a one-one correspondance in the coupled-cluster theory, but the CPHF pseudo diagrams are present in a subtle way. We have studied the {\em pseudo} diagrams in great detail and have shown explicitly their origin in coupled-cluster theory. This is demonstrated by considering the case of the permanent electric dipole moment of atomic Hg and our results are compared with the results of an earlier calculation.

physics.atom-ph↗

arXiv2007

Optical frequency standard with $Sr^+$: A theoretical many-body approach

Demands from several areas of science and technology have lead to a worldwide search for accurate optical clocks with an uncertainty of 1 part in $10^{18}$, which is $10^{3}$ times more accurate than the present day cesium atomic clocks based on microwave frequency regime. In this article we discuss the electric quadrupole and the hyperfine shifts in the $5s ^{2}S_{1/2}\longrightarrow4d ^{2}D_{5/2}$ clock transition in $\mathrm{Sr^{+}}$, one of the most promising candidates for next generation optical clocks. We have applied relativistic coupled cluster theory for determining the electric quadrupole moment of the $4d ^{2}D_{5/2}$ state of $\mathrm{^{88}Sr^{+}}$ and the magnetic dipole ($A$) and electric quadrupole ($B$) hyperfine constants for the $5s ^{2}S_{1/2}$ and $4d ^{2}D_{5/2}$ states which are important in the study of frequency standards with $\mathrm{Sr^{+}}$. The effects of electron correlation which are very crucial for the accurate determination of these quantities have been discussed.

physics.atom-ph↗

arXiv2005

Random Phase Approximation For allowed and Parity Non-conserving Electric Dipole Transition Amplitudes and its connection with Many-Body Perturbation Theory and Coupled Cluster Theory

The connections between the Random Phase Approximation (RPA) and Many-Body Perturbation Theory (MBPT) and its all order generalisation, the Coupled- Cluster Theory (CCT) have been explored. Explicit expressions have been derived for the electric dipole amplitudes for allowed and forbidden transitions induced by the parity non-conserving neutral weak interaction. The Goldstone diagrams associated with the RPA terms in both cases are shown to arise in MBPT and CCT and the numerical verification of this relationship is made for the allowed electric dipole transitions.

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

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

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↗

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

Relativistic coupled-cluster calculation of core ionization potential using the Fock space eigenvalue independent partitioning technique

In this paper we have applied the cluster-expansion ansatz for the wave operator Ωwhich incorporates the orbital relaxation and correlation effects in an efficient manner. We have used both ordinary and normal ordered cluster operator (Ω) to compute the ionization potential for different states of Ne, Ar, and Kr. The result in our calculation clearly shows how the relaxation and correlation effects play the role in determining the ionization potential, one of the interesting aspects in theoretical spectroscopy.

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↗