Firefly and PC GAMESS-related discussion club


 
Learn how to ask questions correctly  
 
 
We are NATO-free zone
 



Can small imaginary frequencies be ignored?

Siddheshwar Chopra
sidhusai@gmail.com


Dear All,
This is a very difficult situation. I have almost tried all the suggestions on this forum to get rid of imaginary frequencies.. But unfortunatley none have worked. I have checked the structure too.
I wish to ask that can we ignore VERY small imaginary frequencies? I have the following ones:

FREQUENCY:        62.07 I     21.98 I     20.05 I     14.22 I     10.76 I      8.02 I      6.86 I  

And in another run:

23.34 I     22.38 I     17.98 I     15.48 I     13.09 I     10.33 I      3.18 I


I read somewhere that low frequencies (especially first or second line) are not vibrations. They should be zero, but are not, due to numerical errors.

Is it correct? Can we safely ignore them? Will the DFT/TDDFT calculations be affected adversely?

In general, is there a thumb rule that we can ignore small frequencies? If yes, then how to decide till which value?

Someone please help.


Regards,



[ Previous ] [ Next ] [ Index ]           Mon Jul 27 '15 2:18pm
[ Reply ] [ Edit ] [ Delete ]           This message read 413 times