I am trying to understand why I can’t get rid of imaginary frequencies for the complexes I am analyzing. The problem exists for both strongly bound (water-water) and weakly bound (nitrogen-nitrogen) complexes.
- I tried optimizing the geometries using a tighter convergence criteria. Optimized geometries resulting from INTERFRAG_TIGHT, GAU_TIGHT, and GAU_VERYTIGHT were passed to frequencies and there are still imaginary frequencies.
- I also tried using analytic gradients and played around with a tighter disp_size and still get imaginary frequencies.
- I even started with optimized geometries from the S66 and A24 databases and am still getting imaginary frequencies.
I attached a couple of example input and output files for the water-water complex.
Are imaginary frequencies just a part of frequency analysis on weakly bound complexes? Or is there something I can do to eliminate them.
Thanks in advance for any help you can provide!