Recent Publications

Tchavdar Todorov

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  1. Title: Ring currents in azulene

    Author(s): Paxton A.T., Todorov T.N., Elena A.M.

    Chemical Physics Letters, 483, No. 1-3, pp. 154-158 (2009)

    doi: 10.1016/j.cplett.2009.10.041

    Full Text

    We propose a self consistent polarisable ion tight binding theory for the study of push–pull processes in aromatic molecules. We find that the method quantitatively reproduces ab initio calculations of dipole moments and polarisability. We apply the scheme in a simulation which solves the time dependent Schrödinger equation to follow the relaxation of azulene from the second excited to the ground states. We observe rather spectacular oscillating ring currents which we explain in terms of interference between the HOMO and LUMO states.

  2. Title: Current-driven atomic waterwheels

    Author(s): Dundas D., McEniry E.J., Todorov T.N.

    Nature Nanotechnology, 4, No. 2, pp. 99-102 (2009)

    doi: 10.1038/nnano.2008.411

    A current induces forces on atoms inside the conductor that carries it. It is now possible to compute these forces from scratch, and to perform dynamical simulations of the atomic motion under current. One reason for this interest is that current can be a destructive force—it can cause atoms to migrate, resulting in damage and in the eventual failure of the conductor. But one can also ask, can current be made to do useful work on atoms? In particular, can an atomic-scale motor be driven by electrical current, as it can be by other mechanisms? For this to be possible, the current-induced forces on a suitable rotor must be non-conservative, so that net work can be done per revolution. Here we show that current-induced forces in atomic wires are not conservative and that they can be used, in principle, to drive an atomic-scale waterwheel.

  3. Title: Current-assisted cooling in atomic wires

    Author(s): McEniry E.J., Todorov T.N., Dundas D.,

    Journal of Physics: Condensed Matter, 21, No. 19 (2009)

    doi: 10.1088/0953-8984/21/19/195304

    The effects of inelastic interactions between current-carrying electrons and vibrational modes of a nanoscale junction are a major limiting factor on the stability of such devices. A method for dynamical simulation of inelastic electron-ion interactions in nanoscale conductors is applied to a model system consisting of an adatom bonded to an atomic wire. It is found that the vibrational energy of such a system may decrease under bias, and furthermore that, as the bias is increased, the rate of cooling, within certain limits, will increase. This phenomenon can be understood qualitatively through low-order perturbation theory, and is due to the presence of an anti-resonance in the transmission function of the system at the Fermi level. Such current-assisted cooling may act as a stabilization mechanism, and may form the basis for a nanoscale cooling 'fan'.