arXiv subjects

B. K. Sahoo

Publications and source records attributed to B. K. Sahoo.

At least 127 records · Page 7Linked to original sources

arXiv2015

Electric dipole moment of $^{225}$Ra due to P- and T-violating weak interactions

We report rigorous calculations of electric dipole moment (EDM) in $^{225}$Ra due to parity and time-reversal violating tensor-pseudotensor (T-PT) and nuclear Schiff moment (NSM) interactions between the electrons and nucleus by employing the relativistic all order coupled-cluster (RCC) methods at various levels of approximation. The most accurate EDM ($d_A$) results are obtained as $d_A=-10.04\times 10^{-20} C_T <σ_n>|e|cm$ and $d_A^{NSM}=-6.79 \times 10^{-17} S (|e|fm^3)^{-1} |e|cm$ with $C_T$ and $S$ are the T-PT coupling constant and NSM respectively. Due to exhaustive treatment of the electron correlation effects in these calculations, the EDM results for the corresponding T-PT and NSM interactions reduce by about 45\% and 23\%, respectively, from the previously known values. Nonetheless they are still found to be 2-3 times larger than the $^{199}$Hg results. Validity of the RCC results are countenanced by comparing our calculations at the zeroth order Dirac-Fock method and all order random-phase approximation with the other groups. In view of the current experimental progress in the $^{225}$Ra EDM measurement, our high accuracy calculations are very useful to yield limits on $C_T$ and $S$ in this atom. Thusly, it is possible to realize more accurate limits on the electron-quark T-PT interaction and $θ_{QCD}$ parameter of particle physics in future.

physics.atom-ph↗

arXiv2015

Correlation Trends in the Hyperfine Structures of $^{210,212}$Fr

We demonstrate the importance of electron correlation effects in the hyperfine structure constants of many low-lying states in $^{210}$Fr and $^{212}$Fr. This is achieved by calculating the magnetic dipole and electric quadrupole hyperfine structure constants using the Dirac-Fock approximation, second order many-body perturbation theory and the coupled-cluster method in the singles and doubles approximation in the relativistic framework. By combining our recommended theoretical results with the corresponding experimental values, improved nuclear magnetic dipole and electric quadrupole moments of the above isotopes are determined. In the present work, it is observed that there are large discrepancies between the hyperfine structure constants of the $7D_{5/2}$ state obtained from the experimental and theoretical studies whereas good agreements are found for the other $D_{5/2}$ states. Our estimated hyperfine constants for the $8P$, $6D$, $10S$ and $11S$ states could be very useful as benchmarks for the measurement of these quantities.

physics.atom-ph↗

arXiv2015

A Relativistic Equation-of-motion Coupled-Cluster Investigation of the Trends of Single and Double Ionization Potentials in the He and Be Isoelectronic Systems

We employ four-component spinor relativistic equation-of-motion coupled-cluster (EOMCC) method within the single- and double- excitation approximation to calculate the single ionization potentials (IPs) and double ionization potentials (DIPs) of the He and Be isoelectronic sequences up to Ne. The obtained results are compared with the available results from the National Institute of Standards and Technology (NIST) database to test the performance of the EOMCC method. We also present intermediate results at different level of approximations in the EOMCC framework to gain insight of the effect of electron correlation. Furthermore, we investigate the dependence of the IPs and DIPs of these ions on the ionic charge and observe that these follow parabolic trends. Comparison between the trends of IPs and DIPs in both the classes of considered systems are categorically demonstrated.

physics.atom-ph↗

arXiv2014

A Relativistic Many-Body Analysis of the Electric Dipole Moment of $^{223}$Rn

We report the results of our {\it ab initio} relativistic many-body calculations of the electric dipole moment (EDM) $d_A$ arising from the electron-nucleus tensor-pseudotensor (T-PT) interaction, the interaction of the nuclear Schiff moment (NSM) with the atomic electrons and the electric dipole polarizability $α_d$ for $^{223}$Rn. Our relativistic random-phase approximation (RPA) results are substantially larger than those of lower-order relativistic many-body perturbation theory (MBPT) and the results based on the relativistic coupled-cluster (RCC) method with single and double excitations (CCSD) are the most accurate to date for all the three properties that we have considered. We obtain $d_A = 4.85(6) \times 10^{-20} < σ> C_T \ |e| \ cm$ from T-PT interaction, $d_A=2.89(4) \times 10^{-17} {S/(|e|\ fm^3)}$ from NSM interaction and $α_d=35.27(9) \ ea_0^3$. The former two results in combination with the measured value of $^{223}$Rn EDM, when it becomes available, could yield the best limits for the T-PT coupling constant, EDMs and chromo-EDMs of quarks and $θ_{QCD}$ parameter, and would thereby shed light on leptoquark and supersymmetric models that predict CP violation.

physics.atom-ph↗

arXiv2014

Long-range interactions between the alkali-metal atoms and alkaline earth ions

Accurate knowledge of interaction potentials among the alkali atoms and alkaline earth ions is very useful in the studies of cold atom physics. Here we carry out theoretical studies of the long-range interactions among the Li, Na, K, and Rb alkali atoms with the Ca$^+$, Ba$^+$, Sr$^+$, and Ra$^+$ alkaline earth ions systematically which are largely motivated by their importance in a number of applications. These interactions are expressed as a power series in the inverse of the internuclear separation $R$. Both the dispersion and induction components of these interactions are determined accurately from the algebraic coefficients corresponding to each power combination in the series. Ultimately, these coefficients are expressed in terms of the electric multipole polarizabilities of the above mentioned systems which are calculated using the matrix elements obtained from a relativistic coupled-cluster method and core contributions to these quantities from the random phase approximation. We also compare our estimated polarizabilities with the other available theoretical and experimental results to verify accuracies in our calculations. In addition, we also evaluate the lifetimes of the first two low-lying states of the ions using the above matrix elements. Graphical representation of the interaction potentials versus $R$ are given among all the considered atoms and ions.

physics.atom-ph↗

arXiv2014

Rigorous limits for hadronic and semi-leptonic CP-violating coupling constants from the electric dipole moment of $^{199}$Hg

Relativistic many-body methods at different levels of approximations are employed to gain insights into the passage of the electron correlations from lower to higher levels in the accurate determination of the electric dipole polarizability ($α_d$) and electric dipole moment (EDM) due to the electron-nucleus tensor-pseudotensor (T-PT) and nuclear Schiff moment (NSM) interactions of the $^{199}$Hg ground state. Moreover, plausible reasons for the differences in the previous calculations are pointed out. Comparison between the calculated and experimental results of $α_d$ indicates that our EDM calculations are about 3\% accurate which in combination with the measured value of $^{199}$Hg EDM yield limits for the T-PT coupling constant $C_T < 2.31 \times 10^{-9}$ and the NSM $S<1.55 \times 10^{-12}|e|fm^3$. From this limit of $S$ and the latest nuclear structure calculation, we get improved limits for the strong CP violating parameter $θ_{QCD} < 2.12 \times 10^{-10}$ and the combined up and down quark chromo-EDMs $(-0.004 \tilde{d}_u + 0.020 \tilde{d}_d) < 1.15 \times 10^{-27} |e| cm$.

physics.atom-ph↗

arXiv2014

Quadrupole Shifts for the $^{171}$Yb$^+$ Ion Clocks: Experiments versus Theories

Quadrupole shifts for three prominent clock transitions, $[4f^{14} 6s] ^2S_{1/2} \rightarrow [4f^{14} 5d] ^2D_{3/2}$, $[4f^{14} 6s] ^2S_{1/2} \rightarrow [4f^{14} 5d] ^2D_{5/2}$ and $[4f^{14} 6s] ^2S_{1/2} \rightarrow [4f^{13} 6s^2] ^2F_{7/2}$, in the Yb$^+$ ion are investigated by calculating the quadrupole moments ($Θ$s) of the $5d_{3/2,5/2}$ and $4f_{7/2}$ states using the relativistic coupled-cluster (RCC) methods. We find an order difference in the $Θ$ value of the $4f_{7/2}$ state between our calculation and the experimental result, but our result concur with the other calculations that are carried out using different many-body methods than ours. However, our $Θ$ value of the $5d_{3/2}$ state is in good agreement with the available experimental result and becomes more precise till date to estimate the the quadrupole shift of the $[4f^{14} 6s] ^2S_{1/2} \rightarrow [4f^{14} 5d] ^2D_{3/2}$ clock transition more accurately. To justify the accuracies in our calculations, we evaluate the hyperfine structure constants of the $6s_{1/2}$, $5d_{3/2,5/2}$ and $4f_{7/2,5/2}$ states of $^{171}$Yb$^+$ ion using the same RCC methods and compare the results with their experimental values. We also determine the lifetime of the $5d_{3/2}$ state to eradicate the scepticism on the earlier measured value as claimed by a recent experiment.

physics.atom-ph↗

arXiv2014

Emending thermal dispersion interactions of Li, Na, K and Rb alkali metal-atoms with graphene in the Dirac model

Using accurate dynamic polarizabilities of Li, Na, K and, Rb atoms, we scrutinize the thermal Casimir-Polder interactions of these atoms with a single layered graphene. Considering the modified Lifshitz theory for material interactions, we reanalyze the dispersion coefficients ($C_3$s) of the above atoms with graphene as functions of separation distance, gap parameter and temperature among which some of them were earlier studied by estimating dynamic polarizabilities of the above atoms from the single oscillator model approximation. All these $C_3$ coefficients have been evaluated in the framework of the Dirac model. The interactions are described for a wide range of distances and temperatures to demonstrate the changes in behavior with the varying conditions of the system and also sensitivities in the interactions are analyzed by calculating them for different values of the gap parameter. From these analyses, we find a suitable value of the gap parameter for which the true nature of the interactions in graphene can be surmised more accurately.

physics.atom-ph↗

arXiv2014

Relativistic equation-of-motion coupled-cluster method for the double ionization potentials of the 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.

physics.atom-ph↗

arXiv2014

Dipole polarizabilities of the transition and post-transition metallic systems

We investigate the role of the electron correlation effects in the calculations of the electric dipole polarizabilities (α) of elements belonging to three different groups of periodic table. To understand the propagation of the electron correlation effects at different levels of approximations, we employ the relativistic many-body methods developed, based on the first principles, at mean-field Dirac-Fock (DF), third order many-body perturbation theory (MBPT(3)), random-phase approximation (RPA) and the singly and doubly approximated coupled-cluster methods at the linearized (LCCSD) and non-linearized (CCSD) levels. We observe variance in the trends of the contributions from the correlation effects in a particular group of elements through a employed many-body method; however they resemble similar tendency among the isoelectronic systems. Our CCSD results are within sub-one percent agreement with the experimental values which are further ameliorated by including the contributions from the important triple excitations (CCSD$_p$T method).

physics.atom-ph↗

arXiv2014

Implementation and Application of the Relativistic Equation of Motion Coupled-cluster Method for the Excited States of Closed-shell Atomic Systems

We report the implementation of equation-of-motion coupled-cluster (EOMCC) method in the four-component relativistic framework with the spherical atomic potential to generate the excited states from a closed-shell atomic configuration. This theoretical development will be very useful to carry out high precision calculations of varieties of atomic properties in many atomic systems. We employ this method to calculate excitation energies of many low-lying states in a few Ne-like highly charged ions, such as Cr XV, Fe XVII, Co XVIII and Ni XIX ions, and compare them against their corresponding experimental values to demonstrate the accomplishment of the EOMCC implementation. The considered ions are apt to substantiate accurate inclusion of the relativistic effects in the evaluation of the atomic properties and are also interesting for the astrophysical studies. Investigation of the temporal variation of the fine structure constant (α) from the astrophysical observations is one of the modern research problems for which we also estimate the αsensitivity coefficients in the above ions.

physics.atom-ph↗

arXiv2014

Relativistic Spectroscopy of Plasma Embedded Li-like Systems with the Screening Effects in the Two-body Debye Potentials

The spectroscopic properties of Li atom and Li-like Ca and Ti ions in the plasma environment are investigated using a relativistic coupled-cluster (RCC) method. Assuming the plasma is of low density and very hot, we consider the Debye model with two approximations by accounting the screening effects: (i) in the nuclear potential alone and (ii) in both the nuclear and the electron-electron interaction potentials. First, the calculations for the energies and the lifetimes of the atomic states are carried out for the plasma free systems in order to check their accuracies following which they are investigated in the plasma environment. It is observed that screenings in the electron-electron interaction potentials stabilize the systems more than the case when the screenings present only in the nuclear potential. Similarly, the earlier predicted blue and red shifts in the $Δn=0$ and $Δn \ne 0$ transition lines (with the principal quantum number $n$) of the Li-like ions change significantly in the case (ii) approximation. The level-crossings among the energy levels are observed for the large screening effects which seem to be prominent in the states of higher orbital angular momentum. The lifetimes of many low-lying states and the relative line-intensities of the allowed transitions are estimated considering different plasma screening strengths.

physics.atom-ph↗

arXiv2014

Relativistic Equation of Motion Coupled-Cluster Method: Application to the closed-shell atomic systems

We report our successful implementation of the full fledged 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+, Al+, K+, Be, and Mg. Four component Dirac spinors are used in the calculations and the one and two electron integrals are evaluated using the Dirac Coulomb Hamiltonian. Our results are in excellent agreement with those available measurements, which are taken from the National Institute of Science and Technology database (NIST). We also present results using the second order many-body perturbation theory (MBPT(2)) and random phase approximation (RPA) in the EOMCC framework. These results are compared with those of EOMCC at the level of single and double excitations in order to assess the role of the electron correlation effects in the intermediate schemes considered in our calculations .

physics.atom-ph↗

arXiv2013

Electric dipole moment of ^{129}Xe atom

The parity (P) and time-reversal (T) odd coupling constant associated with the tensor-pseudotensor (T-PT) electron-nucleus interaction and the nuclear Schiff moment (NSM) have been determined by combining the result of the measurement of the electric dipole moment (EDM) of ^{129}Xe atom and calculations based on the relativistic coupled-cluster (RCC) theory. Calculations using various relativistic many-body methods have been performed at different levels of approximation and their accuracies are estimated by comparing the results of the calculated dipole polarizability of the ground state of the above atom with its most precise available experimental data. The non-linear terms that arise in the RCC theory at the singles and doubles approximation were found to be crucial for achieving high accuracy in the calculations. Our results for the ^{129}Xe EDM due to the odd T-PT interaction and the NSM are, respectively, d_A=0.501 x 10^{-20} C_T <σ_N > |e|cm and d_A=0.336 x 10^{-17} S/(|e| fm^3) |e|cm. These results in combination with the future EDM measurements in atomic Xe could provide the most accurate limits for the T-PT coupling constant and NSM.

physics.atom-ph↗

arXiv2013

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

We employ the closed-shell perturbed relativistic coupled-cluster (RCC) theory developed by us earlier [Phys. Rev. A {\bf 77}, 062516 (2008)] to evaluate the ground state static electric dipole polarizabilities (αs) of several atomic systems. In this work, we have incorporated a class of higher order many-body effects in our calculations that had not been taken into account in the above paper. We highlight their importance in improving the accuracy of $α$. We also calculate the ground state αs of the inert gas atoms and several iso-electronic singly and doubly charged ions in order to make a comparative study of the trends of the correlation effects. Furthermore, we have developed a method to construct intermediate diagrams that are required for the computation of the unperturbed singles and doubles coupled-cluster amplitudes. Our RCC results are compared with those of many-body perturbation theory at different orders to demonstrate the importance of higher order correlation effects for the accurate determination of (αs) of the systems that we have considered.

physics.atom-ph↗

arXiv2013

Dispersion C3 coefficients for the alkali-metal atoms interacting with a graphene layer and with a carbon nanotube

We evaluate separation dependent van der Waal dispersion ($C_3$) coefficients for the interactions of the Li, Na, K and Rb alkali atoms with a graphene layer and with a single walled carbon nanotube (CNT) using the hydrodynamic and Dirac models. The results from both the models are evaluated using accurate values of the dynamic polarizabilities of the above atoms. Accountability of these accurate values of dynamical polarizabilities of the alkali atoms in determination of the above $C_3$ coefficients are accentuated by comparing them with the coefficients evaluated using the dynamic dipole polarizabilities estimated from the single oscillator approximation which are typically employed in the earlier calculations. For practical description of the atom-surface interaction potentials the radial dependent $C_3$ coefficients are given for a wide range of separation distances between the ground states of the considered atoms and the wall surfaces and also for different values of nanotube radii. The coefficients for the graphene layer are fit to a logistic function dependent on the separation distance. For CNT, we have carried out a paraboloid kind of fit dependent on both the separation distances and radii of the CNT. These fitted functions,with the list of fitting parameters, can be used to extrapolate the interaction potentials between the considered alkali atoms and the graphene layer or CNT surface conveniently at the given level of accuracy.

physics.atom-ph↗

arXiv2013

Development of a relativistic coupled-cluster method for one electron detachment theory: Application to Mn IX, Fe X, Co XI and Ni XII ions

We have developed one electron detachment theory from a closed-shell atomic configuration in the relativistic Fock-space coupled-cluster ansatz. Using this method, we determine sensitivity coefficients to the variation of the fine structure constant in the first three important low-lying transitions of the astrophysically interesting highly charged Mn IX, Fe X, Co XI and Ni XII ions. The potential of this method has been assessed by evaluating the detachment energies of the removed electrons and determining lifetimes of the atomic states in the above ions. To account the sensitivity of the higher order relativistic effects, we have used the four component wave functions of the Dirac-Coulomb-Breit Hamiltonian with the leading order quantum electrodynamics (QED) corrections. A systematic study has been carried out to highlight the importance of the Breit and QED interactions in the considered properties of the above ions.

physics.atom-ph↗

arXiv2013

Van der Waals Coefficients for the Alkali-metal Atoms in the Material Mediums

The damping coefficients for the alkali atoms are determined very accurately by taking into account the optical properties of the atoms and three distinct types of trapping materials such as Au (metal), Si (semi-conductor) and vitreous SiO2 (dielectric). Dynamic dipole polarizabilities are calculated precisely for the alkali atoms that reproduce the damping coefficients in the perfect conducting medium within 0.2% accuracy. Upon the consideration of the available optical data of the above wall materials, the damping coefficients are found to be substantially different than those of the ideal conductor. We also evaluated dispersion coefficients for the alkali dimers and compared them with the previously reported values. These coefficients are fitted into a ready-to-use functional form to aid the experimentalists the interaction potentials only with the knowledge of distances.

physics.atom-ph↗