First-principles Study On Transport Property Of Molecular Device With Non-collinear Electrodes

Molecular device is the ultimate electronic devices in the view point sense of scale size.Electron transport in molecular device shows obvious quantum effect,and the transport property of molecular device will be strongly affected by the chemical and structural details,including the contact position and method between the molecule and electrodes,the angle between two electrodes connecting to the molecule.However,we notice that in the existing reports on device simulations from first principles the two electrodes are always in a collinear case.Even for multi-electrode simulations,one usually used to dopt orthogonal electrodes,namely,each pair of the electrodes is in a collinear case.As the electrode configuration will clearly affect the transport property of a device on a nanometer scale,the first principles quantum transport studies with non-collinear electrodes are of great importance,but have not been reported yet.In this paper,we demonstrate the calculations of a transport system with non-collinear electrodes based on the state-of-the-art theoretical approach where the density functional theory(DFT)is combined with the Keldysh non-equilibrium Green's function(NEGF)formalism.Technically,to model a quantum transport system with non-collinear electrodes,the center scattering region of the transport system is placed into an orthogonal simulation box in all the other quantum transport simulations,while one or two electrodes are simulated within a non-orthogonal box.This small change in the shape of the simulation box of the electrode provides flexibility to calculate transport system with non-collinear electrodes,but also increases the complexity of the background coding.To date,the simulation of transport system with non-collinear electrodes has been realized only in the Nanodcal software package.Here,we take the Au-benzene(mercaptan)-Au molecular devices and Co-benzene-Co for example,and systematically calculate the quantum transport properties of the molecular devices with various contact positions and methods,and specifically,we first demonstrate the effect of the angle between the two electrodes on the transport property of molecular device from first principles.In our NEGF-DFT calculations performed by Nanodcal software package,the double ? polarized atomic orbital basis is used to expand the physical quantities,and the exchange-correlation is treated in the local density approximation,and atomic core is determined by the standard norm conserving noilocal pseudo-potential.Simulation results show that the chemical and structural details not only quantitatively affect the current value of the molecular device,but also bring new transport features to a device,such as negative differential resistance.From these results,we can conclude that the physics of a transport system having been investigated in more detail and a larger parameter space such as the effect of the contact model having been assessed by a comparison with "ideal" contacts,further understanding of the transport system can be made and more interesting physical property of the device can be obtained.Based on the theory of first principles,we systematically studied the quantum transport properties of molecular devices,the main innovative results are as follows:(1)The quantum transport properties of Au-benzene(mercaptan)-Au structure molecular devices under different angle and the contact position.Abuot Current Voltage Curve(IVC),Transmission spectrum coefficients(T-E),the Density Of States(DOS),and so on.The work as follows:1)Building the atoms model by Device Studio,calculates the single point energy;2)Change the contact position of the molecular electrode and the Angle between the conductor,calculate IVC,T-E,DOS;3)Replacing hydrogen with sulfur atoms,and comparison Au-mercaptan-Au system and Au-benzene-Au system.which will be useful in designing of emerging electronics.(2)Co-benzene-Co ferromagnetic structure molecular devices PP-180,for example,we studied and analyzed the spin polarization quantum transport properties in parallel spin and antiparallel spin.About the spin injection efficiency(?),the tunnel magnetoresistance ratio(TMR),spin-polarized currents(I?,I?),T-E,PDOS,and so on.The work as follows:calculate the spin of Go and study I?,I?,T-E,PDOS and DOS.The results show that Co electrode molecular devices have high TMR and SIE.