Geometry Optimisation / Frequency (general question)
Jörg Saßmannshausen
jorg.sassm... at strath.ac.uk
Mon Apr 6 17:06:23 UTC 2009
Dear all,
less of specific question, but more a general question.
I am currenty trying to get the geometry optimisation done for a bicyclic
compound. The compound is fairly simple, just C, H, O, N and initially F. As
Axel already has pointed out to me, F can be a bit tricky and indeed I had
negative frequencies (with 2 basis sets I tried) where the F is basically
wobbling around. So I decided to get one step down and replaced F with H.
I have managed to get a converged geometry with these parameters:
&GEO_OPT
MINIMIZER BFGS
MAX_ITER 300
MAX_DR 3.00E-4
RMS_DR 1.50E-4
MAX_FORCE 4.50E-5
RMS_FORCE 3.00E-5
&BFGS
&END
&END GEO_OPT
and
EPS_SCF 1.0E-8
Using the same EPS_SCF 1.0E-8 for the frequency analysis, I get one neg. freq.
at -42.76 1/cm. However, as I remembered from the ADF program, it might be
actually beneficial to use a tighter criterion for the numerical frequency
analysis, so I decreased the value to EPS_SCF 1.0E-8 and loo! now that neg.
frequency has gone.
Is that generally a good idea to run the frequency calculation a bit tighter
than the geometry optimisation or was I just lucky?
I just try to get the grips of the program, hence the question.
Thanks for your help!
JÃ¶rg
--
*************************************************************
JÃ¶rg SaÃŸmannshausen
Research Fellow
University of Strathclyde
Department of Pure and Applied Chemistry
295 Cathedral St.
Glasgow
G1 1XL
email: jorg.sassm... at strath.ac.uk
web: http://sassy.formativ.net
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