  Fast and efficient calculations of optical responses using electromagnetic
models require computational acceleration and compression techniques. A
hierarchical matrix approach is adopted for this purpose. In order to model
large-scale molecular structures these methods should be applied over wide
frequency spectra. Here we introduce a novel parametric hierarchical matrix
method that allows one for a rapid construction of a wideband system
representation and enables an efficient wideband solution. We apply the
developed method to the modeling of the optical response of bacteriochorophyll
tubular aggregates as found in green photosynthetic bacteria. We show that the
parametric method can provide one with the frequency and time-domain solutions
for structures of the size of 100, 000 molecules, which is comparable to the
size of the whole antenna complex in a bacterium. The absorption spectrum is
calculated and the significance of electrodynamic retardation effects for
relatively large structures, i.e. with respect to the wavelength of light, is
briefly studied.
