BSSE-free description of intermolecular force constants in hydrogen fluoride and water dimers

Theoretical studies have been performed to Calculate the force constants and harmonic vibrational frequencies in the hydrogen fluoride and water dimers. The calculations have been undertaken both at the Hartree-Fock and correlated (second-order Moller-Plesset perturbation theory) levels of theory using several different basis sets ranging from the weak to the intermediate. The basis set superposition error (BSSE) has been excluded by using the chemical Hamiltonian approach. The results show that the BSSE influence is significant in the force constants and harmonic vibrational frequencies even if electron correlation is accounted for, so removing the BSSE is important. The results are compared with those obtained by the basis independent density-functional tight-binding method. (C) 2003 Wiley Periodicals, Inc.