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We analyze atomic structures of plasma-embedded aluminum (Al) atom and its ions in the weak- and strong-coupling regimes. The plasma screening effects in these atomic systems are accounted for using the Debye and ion-sphere (IS) potentials for the weakly and strongly coupled plasmas, respectively. Within the Debye model, special attention is given to investigate the spherical and nonspherical plasma screening effects considering in the electron-electron interaction potential. The relativistic coupled-cluster (RCC) method has been employed to describe the relativistic and electronic correlation effects in the above atomic systems. The variations in the ionization potentials (IPs) and excitation energies (EEs) of the plasma-embedded Al ions are presented. It is found that the atomic systems exhibit more stability when the exact screening effects are taken into account. It is also shown that in the presence of a strongly coupled plasma environment, the highly ionized Al ions show blueshifts and redshifts in the spectral lines of the transitions between the states with the same and different principal quantum numbers, respectively. Comparison among the results obtained from the Debye and IS models are also carried out considering similar plasma conditions. [ABSTRACT FROM AUTHOR]

The molecular dipole moment and magnetic hyperfine-structure constant demand an accurate wave function far from the nucleus and in the near nuclear region, respectively. We, therefore, employ the so-called Z-vector method in the domain of relativistic-coupled-cluster theory to calculate the first-order property of molecular systems in their open-shell ground-state configuration. The implemented method is applied to calculate the molecular dipole moment and parallel component of the magnetic hyperfine-structure constant of the SrF molecule. The results of our calculation are compared with the experimental and other available theoretically calculated values. We are successful in achieving good accordance with the experimental results. The result of our calculation of the molecular dipole moment is in the accuracy of ~0.5%, which is clearly an improvement over the previous calculation based on the expectation value method in the four-component coupled-cluster framework [V. S. Prasannaa et al., Phys. Rev. A 90, 052507 (2014)]. Thus, it can be inferred that the Z-vector method can provide an accurate wave function in both the near and far nuclear region, which is evident from our calculated results. [ABSTRACT FROM AUTHOR]

The article deals with the general implementation of the four-component spinor relativistic extended-coupledcluster (ECC) method to calculate first-order property of atoms and molecules in their open-shell ground-state configuration. The implemented relativistic ECC is employed to calculate hyperfine structure constants of alkali metals (Li, Na, K, Rb, and Cs), singly charged alkaline-earth-metal atoms (Be+, Mg+, Ca+, and Sr+), and molecules (BeH, MgF, and CaH). We have compared our ECC results with the calculations based on the restricted active space configuration interaction (RAS-CI) method. Our results are in better agreement with the available experimental values than those of the RAS-CI values. [ABSTRACT FROM AUTHOR]

We report the implementation of the four-component spinor relativistic equation-of-motion (EOM) coupled-cluster method within the single- and double-excitation approximation to calculate the ionization potential of molecules. We have applied this method to calculate vertical ionization potentials of the molecules XH (X = F, CI, Br, I) along with Cl2 and Br2 in their closed-shell configuration. We have also presented intermediate results using the second-order many-body perturbation-theory level in the EOM framework to understand the role of electron correlation. All the calculated values are compared with the available experimental results. Our results are found to be in good agreement with sophisticated experiments, and relative deviation of less than 1% is achieved for all the considered systems. [ABSTRACT FROM AUTHOR]

We report the implementation of the relativistic equation-of-motion coupled-cluster method to calculate the double-ionization spectra (DI-EOMCC) of the closed-shell atomic systems. 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 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 [Y. Noguchi et al., 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. [ABSTRACT FROM AUTHOR]

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+, 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 available measurements, which are taken from the National Institute of Science and Technology database. The accuracies of the calculations are estimated to be within one half of a percent for He-like and Be-like ions and 1% for the heavier systems. We also present results using the second-order many-body perturbation theory and random-phase approximation 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. [ABSTRACT FROM AUTHOR]

We have employed both the Z-vector method and the expectation-value approach in the relativistic coupled-cluster framework to calculate the scalar-pseudoscalar (S-PS) P,T-odd interaction constant Ws and the effective electric field Eeff experienced by the unpaired electron in the ground electronic state of RaF. Further, the magnetic hyperfine structure constants of 223Ra in RaF and 223Ra+ are also calculated and compared with the experimental values wherever available to judge the extent of the accuracy obtained with the employed methods. The outcome of our study reveals that the Z-vector method is superior to the expectation-value approach in terms of accuracy obtained for the calculation of ground-state property. The Z-vector calculation shows that RaF has a high Eeff(52.5 GV/cm) and Ws (141.2 kHz), which makes it a potential candidate for the electric dipole moment of the electron (eEDM) experiment. An estimation of uncertainty associated with our final results is made, and it is found that it lies below 10%. [ABSTRACT FROM AUTHOR]