Subhasish Saha

Bio: Subhasish Saha is an academic researcher from Indian Institute of Technology Patna. The author has contributed to research in topics: Avoided crossing & Photoionization. The author has an hindex of 4, co-authored 6 publications receiving 39 citations.

Shannon entropy as an indicator of correlation and relativistic effects in confined atoms

Abstract: Relativistic and correlation effects in endohedrally confined atoms ($A@{\mathrm{C}}_{60}$) have been investigated using many-body techniques. The endohedral environment is approximated as an atom trapped in a spherically symmetric Gaussian annular square well model potential. The objective of the work is to present Shannon entropy as an indicator of (i) correlation effects and (ii) relativistic effects in confined atoms. The correlation energy in $\mathrm{Be}@{\mathrm{C}}_{60}$ is studied as a function of the depth of the confining potential to give some idea as to how Shannon's correlation entropy is sensitive to the minimum location of correlation energy. To see the prominent relativistic effects in the confined atom, Shannon's relativistic entropy of the valence subshell of $\mathrm{Ba}@{\mathrm{C}}_{60}$ is scrutinized for different confinement parameters. The influence of relativistic and correlation effects on the Shannon entropy of confined atoms is illustrated.

Photoionization phase shift and Wigner time delay of endohedrally confined atoms using transient phase methods

Abstract: In contrast to the conventional finite difference methods, two transient phase methods have been effectively used in the present work to directly compute the photoionization phase shift and Wigner time delay of confined atoms (A@C60) in the single-active electron (SAE) approximation. The different phase methods: (A) employing logarithmic derivatives at shell boundaries, and (B) Born approximation are verified with the help of well-established finite difference methods in SAE approximation and sophisticated many-electron techniques. In this work, confinement oscillations on the dipole phase and photoelectron group delay following ionization from 1s subshell of H@C60, 3p subshell of Ar@C60 and 5p subshell of Xe@C60 are analyzed. The comparison with many-body calculation shows that the features in the time delay of a confined system are governed mainly by the effects of screening apart from that due to the external potential. A systematic study and comparison of the results from phase methods and many-electron techniques indicate that these techniques can be effectively used in the analysis of photoionization phase shift and time delay in confined atoms.

Dramatic Distortion of the $4d$ Giant Resonance by the $C_{60}$ Fullerene Shell

Abstract: The photoionization cross section for the endohedral Xe@C60 atom is investigated within the framework of representing the C60 by a delta-type potential. Results demonstrate that in Xe@C60, the 4d giant resonance is distorted significantly when compared with that of the isolated Xe atom. The reflection of the photoelectron waves by the C60 causes strong oscillations in the photoionization cross section resulting in the replacement of the Xe 4d giant resonance by four prominent peaks. The approximation of C60 by an infinitely thin real potential preserves reasonably well the sum rule for the 4d electrons but modifies the dipole polarizability of the 4d shell.

Shannon information entropy sum of the confined hydrogenic atom under the influence of an electric field

Abstract: In this work, we present the effects of an external electric field on the Shannon entropy sum of a spherically confined hydrogenic atom. The confinement considered is of the impenetrable hard wall type. The electric field modifies the spectrum of the confined hydrogenic system, which results in avoided crossings among the energy levels of the system, with strong competition between the Coulombic and hard wall potential. The results presented indicate that the electric field is a strong candidate to modify information theoretic measures. In addition, we examine the effects of field strength, nuclear charge and hard walls on the minima/maxima structure of the entropic sum. Shannon entropy sum, $$S_t$$ , versus confinement radius, $$R_c$$ , of the 2p level of confined hydrogenic atoms, with field strength $$\epsilon = 0$$ (black), $$\epsilon = 0.001$$ (red), $$\epsilon = 0.01$$ (green) and $$\epsilon = 0.05$$ (blue). The intensity of the field modifies the structure in $$S_t$$ .