Response to “Comment on a critique of the instantaneous normal mode (INM) approach to diffusion” [J. Chem. Phys. 109, 4693 (1998)]

In our original critique [J. Chem. Phys. 107, 4618 (1997)] of the instantaneous normal mode (INM) theory for self-diffusion, we concentrated on atomic Lennard-Jones systems, in which we found a large number of “false-barrier” modes. These are modes which quench to the same local minimum from either side of the imaginary frequency region. We now extend our inquiry to a molecular system (CS2), and find very similar results to what we observed in the atomic system, i.e., a large number imaginary frequency instantaneous normal modes that persist into the crystalline solid.