  Current experimental and theoretical studies on the effect of intermolecular
interactions on molecular conduction appear to be in conflict with each other.
In particular, some experimental results, e.g., the observation of
2-dimensional free-particle character for interface bound electrons indicate
strong intermolecular interactions while other observations indicate an
additive character of conduction properties. In this paper we use a generic
tight binding model with a physically motivated choice of parameters in order
to examine this issue. The model encompasses direct intermolecular interactions
as well as through-metal interactions and can be solved exactly to yield
spectral properties (surface density of states) and transport characteristics
(transmission coefficients and current-voltage behaviors) for single molecule
junctions, molecular islands and molecular layers. We find linear scaling of
conduction properties with the number of conducting molecules in junctions
characterized by molecular layers when the probe (STM tip) addresses different
numbers of molecules; however, the conduction per molecule can differ
significantly from that of an isolated single molecule. When a junction
involves finite molecular islands of varying sizes, linear scaling sets in only
beyond a certain molecular island size, of the order of a few tens of
molecules. Implications for current observation of linear scaling behaviors are
discussed.
