Comparison of theoretical methods for the determination of the protonation and deprotonation energies of NH sub 3 , H sub 2 O, HF, PH sub 3 , H sub 2 S, HCl, and HCN

The structures of the bases NH{sub 3}, H{sub 2}O, HF, PH{sub 3}, H{sub 2}S, HCl, and HCN and the corresponding protonated and deprotonated ions have been optimized by using second-order Moller-Plesset perturbation theory with the 6-31+G(d,p) basis. Basis set superposition errors for computed protonation and deprotonation energies of NH{sub 3} were evaluated for four different basis sets. Single-point calculations on all species were performed with the 6-31+G(2d,2p) basis using the following correlation methods: many-body (Moller-Plesset) perturbation theory at second (MP2), third (MP3), and fourth (MP4) order; the linearized coupled-cluster method (LCCM); the averaged coupled-pair functional (ACPF); configuration interaction with all single and double excitations (CISD); and CISD with the Davidson and the Pople corrections, all relative to a single-reference Hartree-Fock function.