Calculation of refractive indices and local electric field tensors in alpha-sexithiophene crystal

Polarizabilities calculated for sexithiophene using Hartree-Fock and densit y-functional approaches with a 6-31G* basis set are used to calculate refra ctive indices and local electric field tensors in the alpha -sexithiophene crystal. The calculations under-estimate the (incomplete) experimental refr active indices but polarizabilities are devised that fit them. These predic t that the unknown refractive index perpendicular to the crystal be plane i s larger than those in the plane. The tilted molecular long axis produces s izeable off-diagonal local-field components in the crystal ac plane. This c omplicates the analysis of electro-absorption spectroscopy. (C) 2001 Elsevi er Science B.V. All rights reserved.