Distance spline potentials for bond and angle terms. The spline potential (black) is fitted to the sampling (red) from CHARMM dipeptide simulations. Top left: for N1, CA1, and SC1D angle of aspartic acid (N1-SC1D distance); top right: for SC1E-SC2E bond of glutamic acid; bottom left: CO, CA1, and SC1R angle of arginine (CO-SC1R distance); bottom right: CO, CA1, and SC1I angle of isoleucine (CO-SC1I distance).