We have developed an efficient simulation tool 'GOLLUM' for the computation of electrical, spin and thermal transport characteristics of complex nanostructures. The new multi-scale, multi-terminal tool addresses a number of new challenges and functionalities that have emerged in nanoscale-scale transport over the past few years. To illustrate the flexibility and functionality of GOL-LUM, we present a range of demonstrator calculations encompassing charge, spin and thermal transport, corrections to density functional theory such as local density approximation +U (LDA+U) and spectral adjustments, transport in the presence of non-collinear magnetism, the quantum Hall effect, Kondo and Coulomb blockade effects, finite-voltage transport, multi-terminal transport, quantum pumps, superconducting nanostructures, environmental effects, and pulling curves and conductance histograms for mechanically-controlled breakjunction experiments.New J. Phys. 16 (2014) 093029 J Ferrer et al that non-equilibrium transport codes are quite difficult to handle, in part because of their complex input data structures, which can create a steep learning curve, and also because they carry very heavy computational demands. As a consequence, we have devised the new code GOLLUM to be more user friendly, with simple and easy to understand input and output structures, and with no accuracy parameters to tune. We present now a short summary of the features and functionalities of the two programs to better appreciate their differences. SMEAGOL is a non-equilibrium Green's function (NEGF) program that computes the charge and spin transport properties of two-terminal junctions subject to a finite voltage bias. SMEAGOL cannot read a user-defined tight-binding Hamiltonian. Instead, it reads the meanfield Hamiltonian from the program SIESTA [27] and is tightly bound to the old versions of it. SMEAGOL can read from SIESTA Hamiltonians carrying non-collinear spin arrangements as well as the spin-orbit interaction. SIESTA and SMEAGOL have indeed been used successfully to simulate the magnetic anisotropies of atomic clusters [28][29][30] as well as the spin transport functionalities of several atomic chains and molecular junctions subjected to strong spin-orbit interaction [31,32]. However, SMEAGOL does not profit from other recent density functionals. Examples are the van der Waals family of functionals or those based on the local density approximation + U (LDA+U) approach.GOLLUM is a program that computes the charge, spin and electronic contribution to the thermal transport properties of multi-terminal junctions. In contrast to NEGF codes, GOLLUM is based on equilibrium transport theory, which means that it has a simpler structure, is faster, and consumes less memory. The program has been designed for user-friendliness and takes a considerable leap towards the realization of ab initio multi-scale simulations of conventional and more sophisticated transport functionalities.The simpler interface of GOLLUM allows it to read model tight-binding Hamiltonians. Fur...

We report the measurement of conductance and thermopower of C60 molecular junctions using a scanning tunneling microscope (STM). In contrast to previous measurements, we use the imaging capability of the STM to determine precisely the number of molecules in the junction and measure thermopower and conductance continuously and simultaneously during formation and breaking of the molecular junction, achieving a complete characterization at the single-molecule level. We find that the thermopower of C60 dimers formed by trapping a C60 on the tip and contacting an isolated C60 almost doubles with respect to that of a single C60 and is among the highest values measured to date for organic materials. Density functional theory calculations show that the thermopower and the figure of merit continue increasing with the number of C60 molecules, demonstrating the enhancement of thermoelectric preformance by manipulation of intermolecular interactions.

ut. 8., Hungary Experimental correlation analysis and first-principles theory are used to probe the structure and evolution of Ag-CO-Ag single-molecule junctions, both before the formation, and after the rupture of the junctions. Two dimensional correlation histograms and conditional histograms demonstrate that prior to the single-molecule bridge configuration the CO molecule is already bound parallel to the Ag single-atom contact. This molecular precursor configuration is accompanied by the opening of additional conductance channels compared to the single-channel transport in pure Ag monoatomic junctions. To investigate the post-rupture evolution of the junction we introduce a cross-correlation analysis between the opening and the subsequent closing conductance traces. This analysis implies that the molecule is bound rigidly to the apex of one electrode, and so the same single-molecule configuration is re-established as the junction is closed. The experimental results are confirmed by ab initio simulations of the evolution of contact geometries, transmission eigenvalues and scattering wavefunctions.

We present an extensive numerical and experimental study, investigating a threedimensional (3D) granular flow of elongated particles down an inclined plane. Similarly to sheared systems, the average particle orientation is found to enclose a small angle with the flow direction. In the bulk, this behavior is independent of the shear rate. At the surface, however, the particles move in more dilute conditions, and the average orientation strongly depends on the shear rate. A systematic numerical study varying the particle aspect ratio and the plane inclination reveals that the particle size perpendicular to the flow direction, d eff , is an appropriate length scale to define an effective inertial number I eff , which fully captures the impact of the particle shape on the system's rheology. Like in the case of spheres, density and friction result in well-defined functions of the effective inertial number I eff. Thus, we quantify and explain the dependence of the rheological parameters on the aspect ratio, based on the micromechanical details.