negative frequencies of optim. geometry

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eijck
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negative frequencies of optim. geometry

#1 Post by eijck » Fri Oct 29, 2004 1:05 pm

Hi,

I have done a geometry optimisation PREC=accurate and the residual forces are all below 10e-10 eV/A. When I do a freq. calculation a large part of my frequencies are imaginary/negative. I've tried a stepsize POTIM of 0.02 and 0.005, but there's always a large amount of imag.freq's.

The molecule is 4 thiophene rings (C,S,H) and I'm using paw/LDA potentials.

Does anyone have a suggestion what settings to test/check.

I'll send input/output files if needed.

cheers,
Lambert van Eijck
Last edited by eijck on Fri Oct 29, 2004 1:05 pm, edited 1 time in total.

matlgen
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negative frequencies of optim. geometry

#2 Post by matlgen » Tue Apr 12, 2005 9:27 pm

In general, negative (imaginary) frequencies mean that you have found a transition state. Transition states should have (roughly) zero forces, so what you are seeing is consistent. Try moving the atoms along one of the imaginary frequency motions and reoptimizing.
Last edited by matlgen on Tue Apr 12, 2005 9:27 pm, edited 1 time in total.

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