The cocrystal of triphenylphosphine oxide (TPPO) with hydroquinone (HQ) (2:3) were studied theoretically with AM I, PM3, MNDO and MINDO/3 semi-empirical methods to elucidate its structure. The bond lengths and angles from theoretical studies of molecule TPPO/HQ (2:3) were found to be as expected. Theoretical results, concerning with intermolecular van der Waals forces in cocrystal, were compared with the previously obtained experimental data. PM3 method were found to be the best fit for selected C-C, C-P and P-O bond lengths and angles. For the hydrogen bond geometry AMI results were found to be comparable with experimental data. (c) 2005 Elsevier B.V. All rights reserved.