FIG. 3.

Internal-coordinate constraints. (a) For a given ground state conformation ${\stackrel{\rightharpoonup }{r}}_0$ with center of mass ${\mathbf{R}}_{cm}^0$, the basis frames $\left\{{\widehat{\mathbf{x}}}_i^0,{\widehat{\mathbf{y}}}_i^0,{\widehat{\mathbf{b}}}_i^0\right\}$ are obtained for each segment ${\mathbf{b}}_i^0$ such that axis ${\widehat{\mathbf{x}}}_i^0$ lies in the plane defined by the point ${\mathbf{R}}_{cm}^0$ and the vector ${\mathbf{b}}_i^0$, and points towards ${\mathbf{R}}_{cm}^0$. (b) For an arbitrary conformation $\stackrel{\rightharpoonup }{r}$, frames $\left\{{\widehat{\mathbf{x}}}_i,{\widehat{\mathbf{y}}}_i,{\widehat{\mathbf{b}}}_i\right\}$ are obtained in the same way as in (a). The equilibrium (preferred) orientations ${\mathbf{b}}_{i+1}^p$, ${\mathbf{b}}_{i-1}^p$ (shown as translucent surfaces) of segments b_{i + 1}, b_{i − 1} in the frame $\left\{{\widehat{\mathbf{x}}}_i,{\widehat{\mathbf{y}}}_i,{\widehat{\mathbf{b}}}_i\right\}$ correspond to the orientations ${\mathbf{b}}_{i+1}^0$, ${\mathbf{b}}_{i-1}^0$ in the frame $\left\{{\widehat{\mathbf{x}}}_i^0,{\widehat{\mathbf{y}}}_i^0,{\widehat{\mathbf{b}}}_i^0\right\}$.