• S K Das

      Articles written in Pramana – Journal of Physics

    • An electron fluid model for the lattice dynamics of metals

      S K Das D Roy S Sengupta

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      An electron fluid model is proposed for the lattice dynamics of metals which satisfies the requirement of translational invariance and the lattice is in equilibrium without recourse to external forces. The model is applied to calculate the phonon dispersion of sodium in the symmetry directions.

    • Pseudopotential study of lattice parameter and heat of formation for substitutional alloys

      S K Das D Roy

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      Ashcroft’s empty core pseudopotential is applied to the substitutional alloy (K-CS) to calculate the heat of formation and lattice parameter over the entire concentration range. At any concentration the defect crystal is considered to be equivalent to a perfect crystal with a modified lattice parameter and the potential parameter for the defect crystal is calculated by using some suitable interpolation formula. The calculated results agree well with the available experimental results.

    • A modified Ashcroft pseudopotential: application to aluminium

      S K Das D Roy S Sengupta

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      Unified study of the different properties of metals clearly reveals the inadequacy of the empty-core Ashcroft pseudopotential even in the case of simple metals. In the present paper we propose a modification of the one-parameter Ashcroft pseudopotential by assuming the parameterrc to be wave vector-dependent. This introduces a simple modification of the electron-ion pseudopotential in the reciprocal space. The corresponding potential in the configuration space shows that the abrupt change in the Coulomb potential atr=rc is replaced by a continuous change spread over a small region near the core boundary. The present model has been used to make a unified study of Al and is found to be a significant improvement over the simple Ashcroft model. The agreement between the calculated and experimental values is found to be quite satisfactory.

    • Charmed baryon magnetic moments in the covariant oscillator quark model with isospin symmetry breaking

      S K Das C P Singh

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      The magnetic moments of charmed baryons are studied in the covariant oscillator quark model including isospin symmetry breaking effect. In the uncharmed sector, the results differ from those obtained using conventional non-relativistic quark model (nrqm). But in the charmed sector the present values are much nearer to thenrqm results than those calculated using models with hadron mass dependence.

    • A model of knock-out of oxygen by charged particle irradiation of Bi-2212

      S K Bandyopadhyay Pintu Sen P Barat P Mukherjee S K Das B Ghosh

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      A model of knock-out of oxygen by charged particle (α and proton) irradiation of Bi2Sr2CaCu2O8+x (Bi-2212) is proposed on the basis of Monte Carlo TRIM calculations. In Bi-2212, the loosely bound excess oxygen is vulnerable to be displaced by particle irradiation. Binding energy and hence, displacement energy of this loosely bound excess oxygen is less compared to that of stoichiometric lattice bound oxygen and other atoms. The displaced or knocked out oxygen goes to pores or intergranular region and generates large pressure inside the sample. Because of porosity of the material, this displaced oxygen diffuses out and there is a net reduction of oxygen content of the sample. The irradiation induced oxygen knock-out is dominant in the bulk where nonionizing energy loss is maximum.

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