Dear All,
I optimized an organic fluorophore in the ground state using Gaussian 16 program. After optimization, the maximum force, RMS force and RMS displacement were found to be converged. However, the maximum displacement was not converged though the job was terminated successfully. I did not get any imaginary frequency. Could you please suggest how I can resolve this problem?
Please have a look at the attached screenshot regarding the same.
With thanks and regards,
Sitakanta
I would also suggest to add the integral=ultrafine option, and eventually try out a quadratic convergence algorithm (SCF=QC).
This is because that during opt the convergence is judged from an approximated Hessian matrix. At the starting stage of opt, this Hessian is almost accurate, and it is no longer this case when opt goes many steps. Then after the freq calculation, the real accurate Hessian is calculated, and then the program found that it is not fully converged according to the accurate Hessian.
Then the solution is straightforward: Re-run the opt from this structure, and then a new approximated Hessian will be evaluated, which is more close to the accurate one. Or even you can use opt=calcfc or opt=rcfc (if you have one in your chk file). Also you can try opt=tight if it does not work.
scf=qc does not improve this, because there is no problem with the SCF convergence.
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