The permanent dipole moment of gas-phase para-amino benzoic acid revisited

The permanent dipole moment of para-amino benzoic acid has been calculated at various theoretical levels, including Hartree-Fock, second-order M?ller-Plesset perturbation (MP2), coupled cluster singles and doubles (CCSD), and triples corrections CCSD(T), and hybrid density functional theory at B3LYP level. It is found that the B3LYP method fails to provide correct results for the geometry and the permanent dipole moment. These results are significantly improved by MP2 calculations. Our best estimated dipole moments obtained at CCSD and CCSD(T) levels are in good agreement with experiment.