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Bose, S K; Deb, B M; Mukherjee, D
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Accidental degeneracy seems to be the rule rather than an exception amongst thed orbital energies of substituted octahedral complexes ofd^{1} configuration. By using symmetry and physical arguments, in conjunction with firstorder and secondorder degenerate perturbation theory, it is shown that such accidental degeneracies arise in crystalfield theory due to the choice of an inflexible basis set of metal orbitals which neglects the polarisation of metal orbitals by the ligand charges.
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Bamzai, Anjuli S; Deb, B M
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1 Citations
For a closedshell molecule, a connection is drawn between two recent models for molecular shapes, namely, those based on the secondorder JahnTeller (SOJT) effect and the highest occupied molecular orbital (HOMO) postulate respectively. Two necessary and sufficient conditions are derived within the molecular orbital framework for the approximation inherent in the SOJT model to be valid. One of these conditions is akin to the HOMO postulate.
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Deb, B M; Dey, Bijoy Kr.
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1 Citations
The method of local scaling transformation in density functional theory calculates a transformation function (TRF) in order to generate an optimized atomic Nelectron wave function from a trial density and a reference density/wave function. The TRFsf(r) for several atomic systems are studied and it is observed that the number of minima in df(r)/dr equals the number of atomic shells, except whenρ=ρ_{0} andf=r.
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Dey, Bijoy Kr; Deb, B M
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7 Citations
A quantum hydrodynamical study is made of the dynamical changes of a helium atom interacting with lasers of two different intensities, but having the same frequency. Under the intense laser field, electron density oozes out of the helium atom by absorbing laser photons and getting promoted to higher excited states including the continuum. Under the superintense field, electron density partly moves away from the helium nucleus but remains in the “quasibound” dressed states along with the laser field, thus suppressing ionization.
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Gupta, Neetu; Roy, Amlan K; Deb, B M
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9 Citations
Timedependent Schrödinger equation (TDSE) is solved numerically to calculate the ground and first three excitedstate energies, expectation values 〈x^{2j}〉, j=1, 2 …, 6, and probability densities of quantum mechanical multiplewell oscillators. An imaginarytime evolution technique, coupled with the minimization of energy expectation value to reach a global minimum, subject to orthogonality constraint (for excited states) has been employed. Pseudodegeneracy in symmetric, deep multiplewell potentials, probability densities and the effect of an asymmetry parameter on pseudodegeneracy are discussed.
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Deb, B M; Mahajan, Geeta D; Vasan, V S
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7 Citations
According to the openshell CNDO/2 calculations on ClF_{2}, performed by using the computer programme developed by Pople, Beveridge and Dobosh, the molecule is linear and stable, with equilibrium bond length 1.507Å and binding energy −173.7 kcal/mole. The molecule has a tendency to dimerise and to disproportionate into ClF_{3} and ClF. The netdorbital population in the monomer is 0.88. Bonding characteristics and other molecular properties are also discussed.
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By
Gupta, Neetu; Deb, B M
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4 Citations
The quantum dynamics of an electron moving under the HenonHeiles (HH) potential in the presence of external timedependent (TD) laser fields of varying intensities have been studied by evolving in real time the unperturbed groundstate wave function φ (x, y, t) of the HH oscillator. The TD Schrödinger equation is solved numerically and the system is allowed to generate its own wave packet. Two kinds of sensitivities, namely, sensitivity to the initial quantum state and to the Hamiltonian, are examined. The threshold intensity of the laser field for an electron moving in the HH potential to reach its continuum is identified and in this region quantum chaos has been diagnosed through a combination of various dynamical signatures such as the autocorrelation function, quantum ‘phasespace’ volume, ‘phasespace’ trajectory, distance function and overlap integral (akin to quantum fidelity or Loschmidt echo), in terms of the sensitivity towards an initial state characterized by a mixture of quantum states (wave packet) brought about by small changes in the Hamiltonian, rather than a ‘pure’ quantum state (a single eigenstate). The similarity between the HH potential and atoms/molecules in intense laser fields is also analyzed.
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By
Singh, Harjinder; Deb, B M
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3 Citations
Studies on gassurface dynamics have acquired considerable importance recently not only for their intrinsic scientific interest but also for their technological potential. This article first briefly describes various experimental techniques and a number of interesting recent observations resulting from these techniques. It then discusses certain important theoretical methodologies being extensively used nowadays. There arethree broad overlapping streams of theoretical works, viz classical, semiclassical and quantummechanical. There are alsothree basic problems in gassurface interaction, viz (i) the interface presents a manybody problem; (ii) the solid surface is “rough”; (iii) the number of diffractive and inelastic channels is enormously large. The semiclassical approaches appear to dominate over the others in variety and quantity. But the sources of benchmark theoretical results are still the rigorous classicaltrajectory and closecoupling quantummechanical calculations. The coming years are likely to witness not only increased numerical accuracy through refinements in semiclassical and quantummechanical approaches, but also certain special approximate methods designed to yield deeper physical insights into the nature of gassurface interaction.
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