  Destructive quantum interference (QI) has been a source of interest as a new
paradigm for molecular electronics as the electronic conductance is widely
dependent on the occurrence or absence of destructive QI effects. In order to
interpret experimentally observed transmission features, it is necessary to
understand the effects of all components of the junction on electron transport.
We perform non-equilibrium Green's function calculations within the framework
of density functional theory to assess the structure-function relationship of
transport through pyrene molecular junctions with distinct QI properties. The
chemical nature of the anchor groups and the electrodes controls the Fermi
level alignment, which determines the observability of destructive QI. A
thorough analysis allows to disentangle the transmission features arising from
the molecule and the electrodes. Interestingly, graphene electrodes introduce
features in the low-bias regime, which can either mask or be misinterpreted as
QI effects, while instead originating from the topological properties of the
edges. Thus, this first principles analysis provides clear indications to guide
the interpretation of experimental studies, which cannot be obtained from
simple H\"uckel model calculations.
