  We establish a link between quantum mechanical molecular simulations and the
transfer matrix of a molecule. The transfer matrix (T-matrix) of an object
provides a complete description of its electromagnetic response. Once the
T-matrices of the individual components of an ensemble are known, the
electromagnetic response of the ensemble can be efficiently computed. This
holds for arbitrary arrangements of large number of molecules, as well as for
periodic arrays. We provide T-matrix based formulas for computing traditional
chiro-optical properties like Circular Dichroism and Oriented Circular
Dichroism, and also for quantifying electromagnetic duality and electromagnetic
chirality, two properties that are fundamentally related to chiral
interactions, and also technologically relevant. The formulas are valid for
light-matter interactions of arbitrary high multipolar orders. We exemplify our
approach by first computing the T-matrix of a cross-like arrangement of four
copies of a chiral molecule from the time-dependent Hartree-Fock theory
simulation data of the individual molecule, and then computing the
aforementioned electromagnetic properties of both the cross and the individual
molecule. The link that we establish is a necessary step towards obtaining
T-matrix based constitutive relations of general bulk molecular materials from
quantum mechanical simulations of their molecular constituents.
