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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology

Thursday, 24 January 2008
(at 16:30 in room 115, Hallwachsstr. 3)
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Computing electron transport in nano- and bio-devices

Stefano Sanvito

Trinity College Dublin

Density functional theory has revolutionarized our way to do materials science and it is now a fundamental asset for research in Physics, Chemistry, Biology and Nanoscience. This is mainly due to a combination of conceptual simplicity, rigorous theoretical foundation and efficient numerical algorithms. The Smeagol [1, 2] project ( has the ambitious goal of setting the same revolution in the field of ab initio quantum transport. Smeagol, in its present form, calculates the I-V characteristics of nanoscale two-probe devices from first principles. It combines a non-equilibrium transport algorithm capable of evaluating the effects of a steady state current on the electronic structure of the device with density functional theory implemented on a localized atomic orbital basis set. Smeagol is constructed with three main goals in mind. First it must be accurate. For this reason exchange and correlation potentials including strong correlation corrections (LDA+U or LDA+SIC) have been implemented and demonstrated effective for the transport. Secondly, it must be able to scale, and therefore capable of accessing massive parallel machines. Finally it must be reasonably user friendly to serve a large community. In this talk I will review the basic ideas behind the Smeagol project and present some of our results. In particular I will tackle three problems. First I will discuss transport through simple molecules attached to Au leads, and demonstrate that a computational undemanding method for self-interaction correction can yield results in good agreement with experiments. Then I will move to devices sandwiching magnetic molecules (Mn12) between non-magnetic leads and show that the I-V characteristic is a function of the internal degrees of freedom of the molecule itself. This suggests that the electrical read-out of the magnetic state of the molecule is indeed possible. Finally I will tackle the problem of the conductivity of DNA and demonstrate that simulations of devices exceeding several thousands atoms are in the reach of Smeagol\E2??s computational capabilities.
[1] Towards Molecular Spintronics, Alexandre Reily Rocha, Victor Garcia-Suarez, Steve W. Bailey, Colin J. Lambert, Jaime Ferrer and Stefano Sanvito, Nature Materials 4, 335 (2005).
[2] Spin and Molecular Electronics in Atomically-Generated Orbital Landscapes, Alexandre Reily Rocha, Victor Garcia-Suarez, Steve W. Bailey, Colin J. Lambert, Jaime Ferrer and Stefano Sanvito, Phys. Rev. B. 73, 085414 (2006).OA

slides (pdf)

Invited by G. Cuniberti and R. Gutierrez (nanoSeminar)

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