Out-of-Plane BendingΒΆ
Tinker has implemented two types of out-of-plane bending angles. In the Wilson-Decius-Cross formulation [3], the out-of-plane angle \(\chi\) associated with bond BD in Fig. 1 is the angle between BD and plane ADC, whereas the Allinger formulation uses the angle between BD and plane ABC. Similar to harmonic bond stretching, the following functional form has been implemented in Tinker:
\[U = k\chi^2(1 + k_3\chi + k_4\chi^2).\]