I’m wondering if there is a way to speed up the vibrational analysis.
I am running a frequency calculation on a molecule containing 52 atoms for which 307 displacements are needed.
I am running the calculation on 16CPUs and 16GB memory.
The calculation run using Gaussian16 on 8CPU takes roughly 4-5h for optimization and frequency analysis but with these settings, the frequency analysis only in PSI4 1.7 using a pre-optimized structure takes more than 2 days to complete!
For both software I am running calculations at the M06-2X / Def2-SVP level of theory.
Expanding our DFT hessian and TD-DFT capabilities is item #2 on my Psi development priority list. The problems are that #1 (an overhaul of our decades-old I/O system) is going to take a lot of time, and that I’m trying to finish up some research projects and a grant proposal first.
 = There are three “parts” of the Hartree-Fock hessian code that need to be adapted for DFT. There’s the orbital second derivative, the orbital-geometry mixed derivative, and the geometry second derivative. The orbital second derivative part is also needed by TD-DFT, which doesn’t need any other special technology. So getting TD-DFT working is not only simpler than getting DFT hessians, but it’s an excellent correctness test of one of the three major pieces. For those reasons, getting TD-M06-2X is an important stepping stone to getting M06-2X hessians. Incidentally, the path that I foresee is UKS LDA hessians → UKS GGA hessians → RKS GGA hessians → TD-UKS Meta → TD-RKS Meta → UKS Meta hessians → RKS Meta hessians