Hi,
I have performed a gas phase optimisation of a molecule, which has no imaginary frequencies. I have then taken this structure and reoptimised using default cosmo parameters (except for the dielectric constant which is set to 37.5). However, after numerical frequency analysis (using NumForce -central -ri -cosmo) I find several imaginary frequencies. This is not necessarily surprising, but if I use screwer to distort the geometry with respect to the corresponding modes and reoptimise, I end up back with my initial structure, no matter which of the imaginary modes I choose to use in screwer. this suggests that there are no energetic minima with similar geometries. Could the imaginary frequencies be an artifact of the model, and if so, can anyone suggest how I might eliminate them?
Thanks,
Andy