Based on ab initio calculations at MP2 and MP4 levels, a chemically intuitive pi -type hydrogen-bond model is proposed to illustrate and interpret the small deviations from a strictly linear hydrogen bond X . . .H-Y in the dimers (HF)(2), (H2O)(2), and H2O-HF. The computational results show that Jr-type hydrogen-bond interaction is secondary and is an attraction between the H atom of the H-X bond and lone pair on Y. In particular, the orientations of lone pairs are detected, by the energy scan at the MP2/6-311+G (2df, 2p) level with a probing point charge of q = -1, which is important to show the existence of the, pi -type hydrogen bond. Furthermore, the interaction energy of pi -type hydrogen bond, D-pi, and stabilized energy of bent hydrogen bond, DeltaE(sb), are also calculated and discussed.