The interface with Tinker and the rigorous analytical gradients implemented in ddX allow one to perform MD simulations. We tested the MD simulations on two systems (reported in the bottom of table ). For each PDB structure, the input files were prepared using the pdbxyz tool from Tinker and the Amber 99 sb force field , which is bundled in Tinker. The input files were used to run the first 2 ps of NVT MD simulation at a temperature of 300 K, and then the restart files were used to run 2 ps long NVE simulations. The simulations were repeated using two different threshold for the linear solvers of ddX, 10 -4 as a loose threshold and 10 -8 as a tight threshold. These two simple-minded examples show that the forces computed by ddX are indeed accurate, making thus rigorously energy conserving NVE simulations with ddX possible.