NumForce negative frequency

[sv]

Hi,
I calculated a stationary point on the excited state surface by using TD-B3LYP.
But when I calculated frequencies at the excited state surface by using NumForce, I got a negative frequency.
How should I get rid of it? Any comments.

my molecule has c2v symmetry in the ground state and excited state is also optimized in c2v symmetry.

[antti_karttunen]

Hi,

if the negative frequency is small, it might be enough if you redo the optimization with tighter criteria. For NumForce it is often necessary to use at least jobex -gcart 4, often something like jobex -gcart 5 -energy 6 is required. Be sure to use high enough $scfconv, too (I suggest 8 ).

If more strict optimization won't help, it might be necessary to lower the symmetry. Use "screwer" tool to distort the structure towards the negative frequency. You will get new coordinates in $newcoord group of control file, redo the optimization using them. It can also be helpful to visualize the negative frequency with TmoleX or some other software.

[sv]

Thanks antti,
thant helps, I used only $scfconv 7,
so I will increase it and optimize again.

SV