Diffrence in frequencies from ORCA and autode about autode HOT 5 OPEN

Hey @tkpiskorz

Can't say I'm too surprised with this. Neither the opt or normal mode analysis is fully deterministic. ORCA also has access to higher precision quantities. What's the ORCA<->Gaussian difference like?

Also, frequencies at DFT are wrong by ~50 cm-1 so 🤷🏼 (ref. e.g. https://arxiv.org/pdf/2302.04448.pdf)

from autode.

Thanks for quick answer. I am using frequencies to determine bond force constants for MM. The small diffrences are not that important. However, when it changes sign to negative, I am worried that negative frequencies will result in negative bond force constants. Maybe I should not be that worried (as they will contribute only a little).

[edit] :sorry did not mean to close it

from autode.

However, when it changes sign to negative, I am worried that negative frequencies will result in negative bond force constants

Oh yes – that would be very bad!

What's the reason for not computing the force constants numerically and so avoiding horrible coupling(?)

from autode.