Articles written in Pramana – Journal of Physics

    • Composite Anderson-Newns model and chemisorption characteristics of nickel-hydrogen system

      Ravinder Guleria P K Ahluwalia K C Sharma

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      The composite Anderson-Newns model and triangular weighted density of states are used to study the electron density of states, magnetic moment and charge transfer of adatoms for a chemisorbed system. The model has been applied to hydrogen chemisorbed on nickel. It has been observed that with the increase in coverage, number of B-AB states as well as bond strength increases, whereas the magnetic moment and adatom charge decrease with coverage. These results match with the experimental data.

    • Composite Anderson-Newns model and density of states due to chemisorption: Quasi-chemical approximation

      R Guleria P K Ahluwalia K C Sharma

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      In this paper a variation in density of states (DOS) of the substrate due to chemisorption of hydrogen on transition metals using composite Anderson-Newns model has been investigated for different coverages in quasi-chemical approximation of Fowler and Guggenhiem, which in the limitz→∞ gives the Bragg-Williams approximation as a special case. Variation in density of states has been studied for one-dimensional periodic substrate with change in adatom interaction energy and coverage. With increase in coverage, the bonding and antibonding (B-AB) peaks are found to shift towards higher energies and at the same time relative height of the peaks also increases. The interesting feature to observe is that both approximations for a particular coverage, give split-off states with different height for both (B-AB) peaks. It particularly indicates change in B-AB states, representing amount of chemisorption, with the change in interaction energy between adatoms. At the same time bond strength is also found to decrease with interaction between adatoms.

    • Vapour-liquid equilibria of the two- and three-dimensional monoatomic classical fluids interacting via double Yukawa potential

      Y Pathania P K Ahluwalia

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      We have carried out Monte Carlo simulations in Gibbs ensemble for two-and three-dimensional double Yukawa fluid. We have compared liquid-vapour equilibrium curve with that of Lennard-Jones, when parameters occurring in double Yukawa potential are chosen to fit Lennard-Jones potential. The results are in good agreement. The role of repulsive and attractive contributions for the potential on the liquid-vapour coexistence region as well as on critical temperature and critical density has been studied. The critical temperature is found to be more sensitive than the critical density to the variation in repulsive and attractive parts of the potential. Also, the range of the attractive interaction directly influences range of the liquid vapour coexistence region. It has been found that smaller the values of the attractive parameter, larger is the coexistence region.

    • A generalised approach to calculate various transport observables for a linear array of series and parallel quantum dots


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      A systematic generalised approach to find transport observables for a linear array of different quantum dot (QD) systems has been discussed, using non-equilibrium Green function (NEGF) formalism, in the presence of on-dot Coulomb interaction and inter-dot tunnelling. The equation of motion (EOM) method has been used to derive expressions for Green functions (GFs) within the simplest mean-field approximation to tackle the Coulomb correlation term. Starting from the mathematical structures of GFs for single, double and triple quantum dot systems, the expressions for GFs and transport observables have been generalised for the quantum dot systems containing N number of quantum dots in series as well as parallel linear array of dots. Further, the formulae so obtained have been used for numerical calculations of transmission probability and the I –V characteristics of linear arrays of quantum dots in series as well as parallel configuration containing up to three dots. The results show that, with the increase in number of dots in the scattering region, transmission probability and electron current decrease in series case, while both quantities increase in parallel configuration of dots. The inter-dot tunnelling leads to the splitting of transmission peaks in double QD system in series case whereas, it induces Fano effect in triple QD system in parallel configuration.

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