BDT between Au leads Víctor García Suárez

Outline 1) Experiment 2) Previous calculations 3) Electronic and transport properties 4) Other experiments and simulations

1) Experiment

Experiment First transport measurement across a molecular junction Mechanicaly controllable break junction with gold molecules adsorbed on the gold wire surface Reed et al., Science 278, 252 (1997) I-V characteristics Conductance ~ G 0 (up to 0.1 G 0, Tsutsui et al. Appl. Phys. Lett. 89, (2006))

2) Previous calculations

First theoretical calculation BDT molecule connected to ideal electrodes Qualitative agreement between theory and experiment Current and conductace Di Ventra et al., Phys. Rev. Lett. 84, 979 (2000)

Full ab-initio calculation BDT molecule between Au(111) electrodes Zero bias and out of equlibrium Xue and Ratner, Phys. Rev. B 68, (2003) LUMO HOMO Transmission

Other calculations Other coupling configurations Results did not agree with experiments Stokbro et al., Computational Materials Science 27, 151 (2003) Delaney and Greer, Phys. Rev. Lett. 93, (2004) Transmission Correlated electron transport Quantitative agreement for the conductance but not for the I-V

3) Electronic and transport properties

First approximation to the transport properties - Two-level system Each level represents a sulphur level; both levels interact across the central part of the molecule SS Transmission obtained by changing the level coupling Match to the Ab-initio HOMO  

Smeagol results BDT between Au(001) leads SZ basis set; 9 atoms per lead; 93 atoms in total; slightlty stretched Transmission and density of states Phys. Rev. B 80, (2009)

Effect of stretching and I-V BDT between Au(001) under stretching and bias voltage Under strain the junction becomes asymmetric; qualitative I-V agreement Phys. Stat. Sol. 7, 2443 (2007) Effect of stretching Effect of bias

Example of calculation BDT between Au(001) leads with 9 atoms per slice ABAB stacking; coupling on the hollow position (square); distance of 1.9 Å from the surface; periodic boundary conditions along the perpendicular directions; 93 atoms in total

Leads calculation SystemName Au SystemLabel Au NumberOfAtoms 18 NumberOfSpecies 1 %block ChemicalSpeciesLabel 1 79 Au %endblock ChemicalSpeciesLabel %block PAO.Basis Au 1 n= %endblock PAO.Basis %block Ps.lmax Au 1 %endblock Ps.lmax LatticeConstant 1.00 Ang %block LatticeVectors %endblock LatticeVectors AtomicCoordinatesFormat Ang %block AtomicCoordinatesAndAtomicSpecies Au Au 18 %endblock AtomicCoordinatesAndAtomicSpecies %block kgrid_Monkhorst_Pack %endblock kgrid_Monkhorst_Pack xc.functional GGA xc.authors PBE MeshCutoff 200. Ry MaxSCFIterations DM.MixingWeight 0.1 DM.NumberPulay 8 DM.MixSCF1 T DM.Tolerance 1.d-4 SolutionMethod diagon ElectronicTemperature 150 K SaveElectrostaticPotential T BuildSuperCell T InitTransport T BulkTransport T BulkLead LR DM.UseSaveDM T

Extended molecule calculation SystemName Au.em SystemLabel Au.em NumberOfAtoms 93 NumberOfSpecies 4 %block ChemicalSpeciesLabel 1 1 H 2 6 C 3 16 S 4 79 Au %endblock ChemicalSpeciesLabel PAO.EnergyShift 0.02 Ry %block PAO.BasisSizes H SZ C SZ S SZ %endblock PAO.BasisSizes %block PAO.Basis Au 1 n= %endblock PAO.Basis %block Ps.lmax Au 1 %endblock Ps.lmax LatticeConstant 1.00 Ang %block LatticeVectors %endblock LatticeVectors... EMTransport T BuildSuperCell T InitTransport T NEnergReal 500 NEnergImCircle 50 NEnergImLine 30 NPoles 10 VInitial 0.d0 eV VFinal 0.d0 eV NIVPoints 0 Delta 2.d-4 EnergLowestBound -8.d0 Ry NSlices 1 AtomLeftVCte 18 AtomRightVCte 76 TrCoefficients T NTransmPoints 800 InitTransmRange -10.5d0 eV FinalTransmRange -0.5d0 eV PeriodicTransp T UseLeadsGF F HartreeLeadsLeft -6.44d0 Ang HartreeLeadsRight 16.52d0 Ang HartreeLeadsBottom eV DM.UseSaveDM T

Dependence on the lateral size of the electrodes Size of the electrodes a a function of the number of atoms per layer: From 4 to 25 atoms per layer (Au 001)

Dependence on the basis set Type of basis set on the electrodes and molecule: From SZ in the molecule or leads to DZP in all atoms

Dependence on the number of lateral k-points Number of k-points along the perpendicular directions From the  point to 24 k-points

5) Other experiments and simulations

2D conductance histograms of OPE molecules Number of measurements as a function of length and conductance An elliptical zone that moves down as a function of length and another circular zone for very stretched configurations Wandlosky et al. Unpublished (yet)

Simulation of BDT with corrected levels (SAINT) BDT coupled with different atomic configurations and tilt angles Results that agree qualitatively and quantitatively with experiments BDT between Au(111) surfaces Rigid shift of levels

Conductance as a function of angle and coupling atom I Hollow and top configurations Hollow-hollow (not very probable)Hollow-top

Conductance as a function of angle and coupling atom II Top-top Conductance values Top configuration

Fin