"Maximum displacement has NO" in the frequency calculation

aitouna

Hello Everybody, that's my first topic in this forum.
I performed an optimization of an organic molecule using Gaussian 09 software (opt+freq), but when i check the output file
Looking for the convergence criteria of the optimization, and i found that the maximum force, rms force, maximum displacement and rms displacement all has YES,
But the Convergence criteria of the frequency calculation all YES, except the "Maximum displacement has NO".


My question is this : Can i consider this structure is an optimized structure, or all the convergence criteria should have YES, with no exception ?




Sincerely,

wbn

http://sobereva.com/164
Save your final coordinates, and reoptimize your molecule from those with "opt=calcall" keyword added.

我本是个娃娃

http://sobereva.com/278
this is the correct answer.

冰释之川

Generally, the optimized structures with no imaginary frequency (for minima) are acceptable even though  the maximum displacement is NO for frequency calculation. But if you really want the frequency calculation to meet convergence criteria with four yes, you can use the keyword  "opt=calcall" during the geometry optimization which is very time-consuming. In my opinion, it is not necessary in your case provided that the current maximum displacement is not far beyond the corresponding convergence criteria.

sobereva

opt=calcall works for almost all cases, however it is quite expensive.
Therefore, before trying this, I suggest you use "opt=tight freq int=ultrafine" instead of "opt freq", in this case the optimization will be done more precisely. If after frequency analysis, all the four conditions are lower than the convergence thresholds under default setting, that means the optimization has sufficiently converged and the convergence quality is fully acceptable.

aitouna

Thank you all very much for the assistance and help.


Sincerely,

mekelleche

sobereva 发表于 2019-11-16 12:24
opt=calcall works for almost all cases, however it is quite expensive.
Therefore, before trying thi ...

Dear Professor Sobereva,
I performed opt+freq TS berny job in purpose to obtain a transition state, and i get the structure of the transition state but when i check the vibration frequencies i found that the imaginary frequency doesn't belong to formed-broken bonds (dashed bonds), but belong to a methyl group. I repeated the optimisation and i get the same result. How can i solve this weird situation ?

喵星大佬

Adjust the structure and then, take a freq job. Confirm the maximur vibration of imaginary frequency belong to the reaction coordinate and start a opt TS job using this structure.

北大-陶豫

mekelleche 发表于 2021-2-26 08:10
Dear Professor Sobereva,
I performed opt+freq TS berny job in purpose to obtain a transition stat ...

Usually we recommend such a process:
(1) FREEZE the length of the bond which corresponds to your reaction (you should adjust to a proper bond length first, usually 140%~150% the equilibrium length, and if you are not confident, scan it) to remove all other possible imaginery frequencies.
(2) Calculate frequency for the structure to check whether it has the imaginery frequency you desire.
(3) Perform opt=(TS,ReadFC) job.

sobereva

mekelleche 发表于 2021-2-26 08:10
Dear Professor Sobereva,
I performed opt+freq TS berny job in purpose to obtain a transition stat ...

This means your initial guessing geometry is not close to real TS enough, or keywords are inappropriate. I cannot give your more advices without more information of your situation.