arXiv subjects
Publications and source records attributed to Chiranjib Sur.
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.
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.
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.
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.
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.
We report the magnetic dipole and electric quadrupole hyperfine coupling constants of 6 P_{3/2} state of ^{133} Cs(I= {7/2}) obtained from the relativistic coupled cluster (RCC) method. To our knowledge, no prior electric quadrupole hyperfine CC calculation is available for ^{133} Cs(6 P_{3/2}) state. Our computed magnetic dipole (A) and electric quadrupole (B) coupling constants are in excellent agreement with the experiment.
This is a sequel to an earlier article on the theory of angular correlation for double photoionization. Here we consider the two-step double photoionization of a rare gas atom under the influence of a polarized photon beam described by appropriate Stokes parameters. Cylindrical mirror analysers (CMA) are used to detect the outgoing electrons. Theoretical values of the correlation functions are obtained for linearly polarized light. Two different situations is handled. Once, the value of the correlation function is obtained keeping the photo-electron in a fixed direction. The other case the direction of the Auger electron is kept fixed. Comparison with experiments on xenon shows excellent agreement for the case of (4d_{5/2}) photoionization followed by a subsequent (N_{5}-O_{23}O_{23} ^{1}S_{0}) Auger decay for a polarized incident photon of energy (94.5eV) {[}J. Phys.B,
In this paper we have tried to establish a theory for angular correlation between the photo- and Auger electrons in the two-step double photoionization of a rare gas atom. The basic finding of this paper is that a general theoretical expression for the angular correlation function is established in the problem of double photoionization of atoms in the presence of linearly polarized monochromatic light. We consider the case of a xenon atom and the incident light is of (94.5 eV) with arbitrary linear polarization. The theoretical results are compared with the experiments done by K(\ddot{a} )mmerling and Schmidt [J.Phys.B, 26,1141(1993)].
The problem of angular correlation in the double photoionization (DPI) of rare gas atoms is considered in some depth. We refer particularly to the efficiency operator for the detection of an electron by a detector having cylindrical symmetry. The different factors in the efficiency operator are discussed in detail keeping in mind the fundamental epistemological question of the role of the detection process in such experiments.
The problem of angular correlation in the double photoionization (DPI) of rare gas atoms is considered in some depth. We refer particularly to the efficiency operator for the detection of an electron by a detector having the shape of a right circular cylinder. The different factors in the efficiency operator are discussed in detail keeping in mind the fundamental epistemological question of the role of the observer (or his equipment) in such experiments.
We consider the process of double photoionization (DPI) in a rare gas atom as a two-step process, namely (i) photoionization in an inner shell followed by (ii) the emission of an Auger electron from an outer shell. An angular correlation function for the two emitted electrons is defined by analogy with the theory of angular correlation in nuclear physics. An expression is obtained for this angular correlation function by a statistical method which makes use of the density and efficiency operators. The latter takes care of the attenuation of the probability of detection of an electrons due to the geometrical properties of the detector. Theoretical values of the angular correlation function are obtained for DPI in xenon and these are shown to be in good agreement with the experimental results given by Kämmerling and Schmidt.