Exploring the effect of metal electrodes and the transport properties of 4,4′-Di-prop-1-ynyl-biphenyl molecular nanowire using quantum chemical calculation and charge density study

Abstract

A theoretical charge density analysis has been carried out on the organic molecular nanowire 4,4′-Di-prop-1-ynyl-biphenyl (DPBP) using density functional theory (DFT) with the LANL2DZ basis set coupled with the Bader’s theory of atoms in molecules to understand the effect of Au and Pt metal atoms and the external electric field in the molecule. Introduction of Au and Pt atoms in the molecule significantly altered the geometry and the charge density distribution of the molecule. The bond topological analysis of the molecule reveals that, the AuS and PtS bonds exhibit positive Laplacian of electron density [∇2ρbcp(r)] indicates the existence of closed-shell interaction between the metal and the thiol atoms i.e. the non-covalent interaction. The applied electric field changes the conformation as well as the electronic energy levels of molecule rigorously; presumably, this effect may enhance the conductivity of the molecule. Further, the field reduces the HOMO–LUMO gap of Au and thiol substituted DPBP molecule appreciably from −1.8 to −0.7eV; this variation well indicates that, as the field increases, the HOMO and LUMO levels are approach each other. Whereas, in the Pt attached molecule, there is no such kind of features were found for the applied field. The current–voltage characteristics of DPBP molecule has been calculated theoretically using Landaure formalism. The conductivity of Pt substituted DPBP molecule is notably higher than Au substituted molecule.