was treated as a four-coordinated Zn (denoted zn4 n4). In Zn3trig, zn3 n3 were treated as zn4 n4 in all their interactions with other atoms, except for the N-Zn-N angle which was changed from the tetrahedral angle (arccos(-1/3) ≈ 109.47 • ) to 120 • , using the same spring constant.