Quadrupole moment calculations for some aromatic hydrocarbons

Quadrupole tensor calculations are reported for benzene, naphthalene, anthracene, phenanthrene, biphenyl (planar and twisted), pyrene, [18]-annulene and azulene. Double-zeta and STO/4G basis sets give similar ratios between naphthalene and benzene components. STO/4G calculations give out-of-plane components proportional to the number of valence electrons for all molecules except azulene.