  We present density functional theory (DFT) based non-equilibrium Green's
function (NEGF) calculations for the conductance through a nitrobenzene
molecule, which is anchored by pyridil-groups to Au electrodes. This work is
building up on earlier theoretical studies where quantum interference effects
(QIE) have been identified both in qualitative tight binding and in DFT
descriptions for the same molecule with different chemical connections to the
leads. The novelty in the current contribution is two-fold: i) The
pyridil-anchors guarantee for the conductance to be determined by rather narrow
peaks situated closely to the Fermi energy which is relevant because it might
maximize the impact of quantum interferences on the I/V behaviour. In a scan of
eight different junction setups, where the connection sites of aromatic rings,
their torsion angle with respect to each other and the surface structure have
been varied, QIE was found to dominate the conductance for only one planar
geometry. For finite torsion angles between aromatic rings the effect moves to
higher energies and would therefore only be accessible for experimental
observation in a gated junction. ii) A detailed comparison between simple
topological models and DFT results for the investigated systems aims at
assessing the usefulness of such models as analysis tools for a better
understanding of the physics of QIE and its structure dependence.
