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Upendra Harbola

Publications and source records attributed to Upendra Harbola.

6 recordsLinked to original sources
PubMed2006

Simulation of single molecule inelastic electron tunneling signals in paraphenylene-vinylene oligomers and distyrylbenzene[2.2]paracyclophanes.

Inelastic resonances in the electron tunneling spectra of several conjugated molecules are simulated using the nonequilibrium Greens function formalism. The vibrational modes that strongly couple to the electronic current are different from the infrared and Raman active modes. Spatially resolved inelastic electron tunneling (IET) intensities are predicted. The simulated IET intensities for a large distyrylbenzene paracyclophane molecule are in qualitative agreement with recent experimental results.

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PubMed2006

Nonequilibrium superoperator GW equations.

Hedin's equations [Phys. Rev. 139, 796 (1965)] for the one-particle equilibrium Green's function of a many-electron system are generalized to nonequilibrium open systems using two fields that separately control the evolution of the bra and the ket of the density matrix. A closed hierarchy is derived for the Green's function, the self-energy, the screened potential, the polarization, and the vertex function, all expressed as Keldysh matrices in Liouville space.

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PubMed2005

Nature of the entropy versus self-diffusivity plot for simple liquids.

The empirical relation (D(*))(alpha) = a exp[S] between the self-diffusion coefficient D(*) and the excess entropy S of a liquid is studied here in the context of theoretical model calculation. The coefficient alpha is dependent on the interaction potential and shows a crossover at an intermediate density, where cooperative dynamics become more important. Around this density a departure from the Stokes-Einstein relation is also observed. The above relation between entropy and diffusion is also tested for the scaled total diffusion coefficient in a binary mixture.

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PubMed2002

Anomalous stretching in a simple glass-forming liquid.

The frequency dependent shear modulus G(omega) for a simple liquid shows strongly stretched behavior and the stretching exponent increases with decrease of temperature. This unconventional behavior was reported earlier in Phys. Rev. Lett. 73, 963 (1994) from experiments on simple liquids. We demonstrate here that this is a feature of the characteristic two-step relaxation process of the self-consistent mode coupling theory of supercooled liquids.

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PubMed2002

Model for glass transition in a binary fluid from a mode coupling approach.

We consider the mode coupling theory (MCT) of glass transition for a binary fluid. The equations of nonlinear fluctuating hydrodynamics for the compressible fluid are obtained with a proper choice of slow variables which correspond to the conservation laws in the system. The resulting model equations are used to obtain a coupled set of nonlinear integro-differential equations for the various correlations of partial density fluctuations. These equations are then solved self consistently in the long-time limit to locate the dynamic transition in the system. The transition point from our model is at considerably higher density than predicted in the other existing MCT models for binary systems.

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