(1) the heavy-atom participants in the candi-date bond were oxygen, nitrogen, fluorine, or sulfur atoms. In oursystem, only oxygen atom was considered as the heavy-atom par-ticipant. (2) The radius for donor–acceptor pairs was no farther than3.5˚A apart. (3) The angle of the hydrogen–donor–acceptor was lessthan 30◦. (4) The hydrogen bond as defined above was present inat least 75% of the frames of the trajectory.