Molecular Electronics on the NWGrid

Steven W.D. Bailey.

Colin Lambert, Iain Grace, Victor Garcia-Suarez,Skon Sirichantaropass and Chris Finch.

SMEAGOL: a Tool for Molecular Electronics

V. M. García-SuárezA. R. RochaS. W. BaileyS. SanvitoJ. FerrerC. J. Lambert

S pin and

M olecular

E lectronics in an

A tomically

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L andscape

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V. M. García Suárez

Collaborations are wellcomeAcademic Licensehttp://www.smeagol.tcd.ie

SMEAGOL: a computational tool for molecular- and spin-electronicsRocha, García Suárez, Bailey, Lambert, Ferrer and SanvitoSubmitted to Phys. Rev. B

SMEAGOLPublications

Engi

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V. M. García Suárez

Dr. Alexander Reily Rocha. Dr. Victor Garcia Suarez. Dr. Steve Bailey. Prof. Colin Lambert. Prof Jaime Ferrer and Dr. Stefano Sanvito

Transport ← SIESTA ↔ Non-equilibrium transport(Zero bias) (DFT) (Finite bias)

(2) (1) (3)

http://www.smeagol.tcd.ie/

Details of the calculation have been published in the following journals;

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).

Spin and Molecular Electronics on an Atomically-Generated Orbital Landscape, Alexandre Reily Rocha, Victor Garcia-Suarez, Steve W. Bailey, Colin J. Lambert, Jaime Ferrer and Stefano Sanvito, Phys. Rev. B. (In press 2006)

Also cond-mat/0510083.

Phenyl ringsDr. V. Garcia-Suarez and Skon Sirichantaropass

• Small systems are relaxed by molecular dynamics within SMEAGOL.

Au/Si - C - C - Benzene - C - C - Si/Au

Au

Si

Highest occupied molecular orbital is the valence band.

Lowest unoccupied molecular orbital is the conduction band.

HOMO LUMO

Molecule building blocksMolecule building blocksThis family of molecules shares the same transport features close to the Fermi energy

Surfaces of Surfaces of constant LDOS constant LDOS (local density (local density of states)of states)

Conformation dependence of molecular conductance: chemistry versus geometryC. M. Finch, S. Sirichantaropass, S. W. Bailey, I. M. Grace, V. M. Garcıa-Suarez and C. J. LambertDepartment of Physics, Lancaster University, Lancaster, LA1 4YB,U. K.(Dated: March 16, 2007)

The European Commission and the British EPSRC, DTI, Royal Society, and NWDA. CMF thanks QinetiQ for funding through Agreement No. CU016-48671.VMGS thanks the EU network MRTN-CT-2004-504574 for a Marie Curie grant.

NWGrid for computing resources

Recent experiments by Venkatamaran et al. [Nature (London) 442, 904 (2006)] on a series of molecular wires with varying chemical compositions, revealed a linear dependence of the conductance on cos2µ, where µ is the angle of twist between neighboring aromatic rings. To investigate whether or not this dependence has a more general applicability, we present a first principles theoretical study of the transport properties of this family of molecules as a function of the chemical composition, conformation and the contact atom and geometry. If the Fermi energy EF lies within the HOMO-LUMO gap, then we reproduce the above experimental results. Moregenerally, however, if EF is located within either the LUMO or HOMO states, the presence of resonances destroys the linear dependence of theconductance on cos2µ and gives rise to non-monotonic behaviour associated with the level structure of the different molecules. Our results suggest that the above experiments provide a novel method for extracting spectroscopic information about molecules contacted toelectrodes.

GGA-relaxed configurations of all molecules studied in thiswork capped with NH2. Grey, green, blue, red and orange vertexescorrespond to H, C, N, F and Clatoms.

We find that geometry is the dominant factor when the Fermi level sits inside the HOMO-LUMO gap, since different side groups do not affectthe linear dependence. However, when the Fermi level approaches either the HOMO or LUMO resonances, chemistry comes into play, because the chemical composition of the pristine molecules causes the positions of the HOMO and LUMO resonances to differ from molecule to molecule.

What is it ?• C50 is an unstable fullerene.

• Decachlorofullerene[50] is a stable fullerene.

• C50Cl10┴@(11,11) & C50Cl10║@(11,11) are stable, exothermic carbon nanotube peapods (CNP’s).

Charge distribution.

LDOS Potential/charge

Carbon nanotube electron turbines: a novel design for nano-motors.

Conclusion

• The NWGrid has allowed our research group to develop codes which need the full capabilities on offer to be fully functional. A whole generation of young UK based scientists can feel secure in the knowledge that they can be at the forefront of research in our field.