Solids modelled by crystal field ab initio methods. 5. The phase transitions in biphenyl from a molecular point of view

Using ab initio calculations at the 4-21G level and procedures for extrapolation to r g geometry as well as using the electrostatic crystal field (ECF-MO) approach, the geometry and torsion potential were calculated for 1,1'-biphenyl in the gas phase, in the P2 1 /a lattice with Z=2 and in the Pa lattice with Z=4. At all stages excellent agreement is obtained with available diffraction data, including L 22 librational components between 293 and 40 K. The following molecular picture emerged when the molecule goes from the gas phase through the solid-state phases biphenyl I, biphenyl II and biphenyl III