I am having trouble with a difficult convergence in Gaussian16. I am running two separate PES scans for hindered rotors in my molecule that will eventually be used in subsequent rate calculations. I decided to back down the optimization convergence criteria for one of the scans from verytight to tight, as looking at the criteria in the failed runs shows that it is getting very close but not close enough to finally converge, at which point the displacement and RMS displacement begin to increase.
I've also thought about changing the SCF algorithm or increasing my integration grid, however, the grid is already at ultrafine and I am trying to minimize the use of SUs.
The issue is that I already have the other PES scan that has been running for a while and is using the opt=verytight criteria and I'm worried that using both PES scans together for the rate calculation might not be valid. However, since they are both using the same model chemistry, (i.e. functional, basis set, integration grid, etc) just with different convergence thresholds, it may not be the worst thing in the world (Albeit, not ideal).
- Is it valid or invalid to calculate the PES of two hindered rotors on the same molecule with different convergence criteria?
If someone can confirm/reject the following, that would be great also:
I'm currently under the impression that since this is not a direct comparison between
two energies, rather, the optimization is being done to find the PES for a rotor, its not that big of a deal.