geometry optimization: how to fight negative frequencies

[Miro]

Hello,

finding the minimal gemetry is sometimes tough, one has to try many "tricks".

I would like to ask concerning this older post:

https://nwchemgit.github.io/Special_AWCforum/st/id2535/Trouble_with_negative_frequencie....html

Is the "huge" grid already introduced ?

Are there any new tips and tricks on geometry optimization in the newest release version ?

Best, Miro

[Niri Govind]

Hi Miro,

The grid huge option is available now.

https://github.com/nwchemgit/nwchem/wiki/Density-Functional-Theory-for-Molecules

Do you have a specific case(s) you are having issues with ?

Best,

-Niri 

Niri Govind

PNNL

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[Miro]

Hi Niri,

thanks for the hint !

Now, after trying and summarizing, I got this "silver bullet"  for successful geometry optimizations:

dft 

   grid huge 

end

driver

  clear

  tight

  linopt 0

  maxiter 100

end

Miro

[Miro]

Hello Niri,

upon testing my "silver bullet" with larger organic molecules, I got only one "negative zero" after  geometry optimizations, see below. I think the final geometry is good, right ?

 ----------------------------------------------------------------------------

 Normal Eigenvalue ||           Projected Infra Red Intensities

  Mode   [cm**-1]  || [atomic units] [(debye/angs)**2] [(KM/mol)] [arbitrary]

 ------ ---------- || -------------- ----------------- ---------- -----------

    1       -0.000 ||    0.000001           0.000         0.001       0.001

    2        0.000 ||    0.000008           0.000         0.008       0.005

    3        0.000 ||    0.000015           0.000         0.015       0.008

    4        0.000 ||    0.000007           0.000         0.006       0.004

    5        0.000 ||    0.000005           0.000         0.005       0.003

    6        0.000 ||    0.000014           0.000         0.014       0.008

    7       17.703 ||    0.000684           0.016         0.667       0.385

    8       20.122 ||    0.000084           0.002         0.082       0.047

On Saturday, 30 January 2021 at 20:22:05 UTC+1 niri....@gmail.com wrote: