The photosynthetic light-harvesting system II (LH2) of Rhodospirillum molischianum is investigated using a time-dependent combination of molecular dynamics simulations and semiempirical ZINDO/S electronic structure calculations. The classical simulations are performed on the available crystal structure of the LH2 complex. Snapshots of the atomic fluctuations along this 12 ps long trajectory serve as input for the calculation of the excitation energies of the individual bacteriochlorophylls embedded in the LH2 complex. Furthermore, the couplings between the bacteriochlorophylls are computed using the method of transition charges from electrostatic potentials and for comparison also using the point-dipole approximation. With these quantities the excitonic energies of the complete system as well as the linear absorption spectra are calculated and compared to experimental findings.