The density functional theory calculations were carried out to determine the influence of the structure of the radical cation dimer pair of model aromatic molecules on the principal values of a g-tensor. The calculated results for different model structures of (naphthalene)(2) and (p-dimethylenebenzene)(2) and individual model naphthalene and p-dimethylenebenzene molecules were analyzed by comparing results of calculations for different models. This comparison predicts an analogous effect for g-tensor principal values of P-700(+) special dimer pair radical cation in core Photosystem I and for g-tensor principal values of the p(700)(T) special dimer pair triplet radical in core Photosystem I. The change in the g-tensor principal values in stacked structures of p-terphenyl cation radical was deduced from an extended model stacked multimer structure. (c) 2005 Elsevier B.V. All rights reserved.