An ab initio approach was utilized to explore the electronic transport properties of 4'-thiolate-biphenyl-4-dithiocarboxylate (TBDT) sandwiched between two electrodes made of various materials X (X = Cu, Ag, and Au). Analysis of current-voltage (I-V) characteristics, rectification performance, transmission functions, and the projected density of states (PDOS) under various external voltage biases showed that the transport properties of these constructed systems are markedly impacted by the choice of electrode materials. Further, Cu electrodes yield the best rectifying behavior, followed by Ag and then Au electrodes. Interestingly, the rectification effects can be tuned by changing the torsion angle between the two phenyl rings, as well as by stretching the contact distances between the end group and the electrodes. For Cu, the maximum rectifying ratio increases by 37 % as the contact distance changes from 1.7 Å to 1.9 Å. This is due to an increase in coupling strength asymmetry between the molecule and the electrodes. Our findings are compared with the results reported for other systems. The present calculations are helpful not only for predicting the optimal electrode material for practical applications but also for achieving better control over rectifying performance in molecular devices.

We have performed first-principle calculations based on density functional theory (DFT) and non-equilibrium greens functions (NEGF) for calculating the charging energies of molecular system weakly coupled to an environment. We apply this approach to the molecule naphthalene, which is lying flat on gate dielectric between the source and drain electrodes. Our calculated values of charging energy for naphthalene in an isolated case are in good agreement with experimental values. Further, in an electrostatic environment, the result shows renormalization of molecular energy levels and therefore reduces the charging energy of naphthalene. Subsequently, the charge stability diagram of naphthalene based single-electron transistor (SET) has been obtained by calculating the charging energies as a function of an external gate potential. This diagram shows the dependence of SET conductance on the gate voltage and the source-drain bias. Our implementation is intended to predict the charging energies of the naphthalene-based SETs that reveals further scope in realization of the devices at nanoscale.

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