Criteria for the formation of a salt bridge. A salt bridge is considered to be formed if the distance between any of the oxygen atoms of acidic residues and the nitrogen atoms of basic residues are within the cut-off distance (default 3.2 Angstroms) in at least one frame.The default distance cut-off can be changed by the user.he search can be restricted to a selection and/or a frame range given by the user. A salt bridge is considered to be formed if the distance between any of the oxygen atoms of acidic residues and the nitrogen atoms of basic residues are within the cut-off distance (default 3.2 Angstroms) in at least one frame.