PMFLib offers two collective variables, WORMPOS and WORMANG, for the description of the mutual position of a macrocycle (host) and an axle (guest) in a complex. Their mathematical definition is rather intricate. Therefore, we will here provide only their setup and geometrical meaning.

The collective variable WORMPOS aims to determine the parametric position of the guest towards the host. The position is defined by the intersection between the guest worm-like representation and the plane representing the host. The guest can be discretized by control points corresponding to centers of masses (COMs) of selected guest fragments. The plane is obtained by the root-mean-square fit to selected atoms of the host. Since the guest can be naturally bent, there might be more intersections. Thus, the intersection is searched only within a selector zone represented by a sphere centered on the host COM. The parameters of the selector zone (seldist and steepness parameters) ensure that only the intersection occurring in the host cavity is considered.

The supplementary collective variable WORMANG is defined as an angle between the normal vector of the plane and a worm segment within the selector zone.