MICROSCOPIC CALCULATION OF THE ELECTROABSORPTION SPECTRA OF POLYACENECRYSTALS

A two-dimensional analogue of the Merrifield model of the coupling bet ween the Frenkel and charge transfer (CT) excitations of a molecular c rystal is applied for the calculation of the electroabsorption (EA) sp ectra of polyacene crystals. The approach is essentially nonempirical, with most of the necessary input data estimated either from theoretic al calculations or from independent experiments. Good agreement betwee n the calculated and experimental EA spectra lends credence to the mod el and allows us to draw conclusions concerning the accuracy of band g ap estimates based on polarisation energy calculations. The conclusion s may be potentially useful for other molecular crystals.