  Site density functional theory (SDFT) provides a rigorous framework for
statistical mechanics analysis of inhomogeneous molecular liquids. The key
defining feature of these systems is the presence of two very distinct
interactions scales (intra- and inter-molecular), and as such proper
description of both effects is critical to the accuracy of the calculations.
Current SDFT applications utilize the same approximation scheme for both
interaction motifs, which negatively impacts the results. Dual space
methodology, used in this work, alleviates this issue by providing the
flexibility of evaluating part of the interactions in traditional field
representation. For molecular liquid this translates into retaining density
representation for inter-molecular interactions but describing stiff
intra-molecular remainder by more appropriate conventional field based methods.
This opens the way to decouple analysis of the two interactions scales - the
idea which is developed further in this work for the case of homogeneous
reference approximation of inter-molecular interactions. We demonstrate that by
defining new collective variables, the behavior of the original molecular
liquid system at the inter-molecular level can be transformed to resemble that
of an effective simple fluid mixture. The latter is linked to intra-molecular
scale through renormalized interaction parameters. We illustrate this
renormalization procedure for several types of diatomic liquids, showing that
this approach cures many of the shortcomings of existing SDFT methods.
