The optimized geometry and vibrational frequencies have been determined for biphenylene using isolated molecule and periodic DFT calculations. The results correspond exceedingly well with the observed inelastic neutron scattering spectrum and the structure deduced from X-ray diffraction measurements at 130 K. The extent of agreement shows that this combination of theory and experimental methods is suitable for detection and confirmation of relatively small structural effects whose detection by diffraction studies may be compromised by crystal disorder. In the case of biphenylene this interest stems from the fact that it is the epitomical Mills-Nixon molecule. (c) 2006 Elsevier B.V. All rights reserved.