Model calculations are described for both pure (MX) and mixed-halide (MXxX′1-x) halogen (X)-bridged transition metal (M) linear chain complexes in terms of an extended Peierls-Hubbard, tight-binding Hamiltonian with ¾-filling oftwo-bands. Both inter- and intra-site electron-phonon coupling are included as well as various electron correlations. Calculated properties include electronic (optical absorption), lattice dynamic (IR, Raman) and spin (ESR) signatures for the ground states, localized excited states produced by impurities, doping or photo-excitation-excitons, polarons, bipolarons, solitons; and the edge states (which occur in mixed-halide crystals, e.g. PtClxBr1-x). Adiabatic molecular dynamics is used to explore photodecay channels.