Small negative frequency after relaxation

[mikkkee]

Hi, I am using B3LYP for relaxation of HfO2 defect system.

In my calculation, the convergence conditions were EDIFF=1E-4;EDIFFG=-0.05. NSW was set to 60. After 60 ionic steps, EDIFFG=-0.05 was not reached. The largest force was about 0.09 eV/angstrom.

I then checked the frequencies for the system after relaxation and found 3 small negative frequencies (5.68, 7.32, 10.21 cm-1):

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  64 f/i= 0.170327 THz  1.070198 2PiTHz 5.681508 cm-1  0.704418 meV
  65 f/i= 0.219475 THz  1.379001 2PiTHz 7.320892 cm-1  0.907675 meV
  66 f/i= 0.306052 THz  1.922983 2PiTHz 10.208803 cm-1  1.265731 meV

Other frequencies are:

the largest

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 1 f  = 24.876753 THz 156.305247 2PiTHz  829.799125 cm-1 102.882016 meV
 2 f  = 24.510721 THz 154.005404 2PiTHz  817.589635 cm-1 101.368232 meV

...

the smallest

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 62 f = 2.231141 THz 14.018675 2PiTHz 74.422865 cm-1 9.227263 meV
 63 f = 1.684326 THz 10.582932 2PiTHz 56.183062 cm-1 6.965814 meV

Are these small frequencies acceptable? How can I eliminate them?

Also, I used this structure as a reactant to do transition state search by NEB.
In the image with highest energy, there exist 4 negative frequencies: 3 small negative frequencies and 1 big negative frequency. (as below, 3.52, 4.86, 6.25, and 69.81 cm-1)

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 63 f/i= 0.105598 THz 0.663491 2PiTHz 3.522365 cm-1 0.436718 meV
 64 f/i= 0.145844 THz 0.916366 2PiTHz 4.864840 cm-1 0.603164 meV
 65 f/i= 0.187444 THz 1.177747 2PiTHz 6.252469 cm-1 0.775208 meV
 66 f/i= 2.092793 THz 13.149407 2PiTHz 69.808064 cm-1 8.655100 meV

Can I accept this structure as the transition state? Is this result reliable consider the 3 negative frequencies?

<span class='smallblacktext'>[ Edited ]</span>

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