ABINITIO STUDY OF THE STRUCTURE AND DIPOLE-MOMENT OF AZULENE

The two structures of azulene with C2v and C(s) symmetry, their energy difference and their dipole moments have been investigated via ab initio quantum mechanics. Self-consistent-field (SCF) theory was used in conjunction with various basis sets up to TZP+f quality. The SCF method fails to predict the correct minimum energy structure (C(s) instead of C2v) due to the neglect of electron correlation. MP2 wavefunctions were used to analyze different correlation contributions which reduce the SCF value of the dipole moment mu by almost-equal-to 0.5 D. The application of the MR-SDCI method yields mu=0.93 D in good agreement with the experimental value (mu(exp)=0.79 D). The results are discussed by means of perturbation theory. Additionally, the azulene ''sandwich'' dimer was investigated al several internuclear distances to explore the origin of the disordered crystal structure.