UT theoretical chemistry code forum

Hi!

I simulated a CO molecule adsorbing onto the MnO surface (with C on top of Mn) using IBRION = 5 and NFREE = 2. And I got 6 frequencies in the OUTCAR:

1 f = 61.660865 THz 387.426644 2PiTHz 2056.785017 cm-1 255.008933 meV
2 f = 4.306939 THz 27.061296 2PiTHz 143.664019 cm-1 17.812075 meV
3 f = 3.485615 THz 21.900767 2PiTHz 116.267606 cm-1 14.415351 meV
4 f = 2.825795 THz 17.754994 2PiTHz 94.258373 cm-1 11.686553 meV
5 f = 0.772404 THz 4.853157 2PiTHz 25.764619 cm-1 3.194407 meV
6 f/i= 0.599697 THz 3.768010 2PiTHz 20.003752 cm-1 2.480150 meV

I know the first frequency (2056cm-1) is the CO stretch so which of the following stands for the stretch between C and Mn?
Also, what do the other frequencies stand for? Frequency 6 has a "/i" attached to it, what does it mean?

I have attached the OUTCAR file of this calculation. Thank you!

First, note that this question unrelated to our vtstcode and so is more appropriate for the vasp guys.

That said, yes, the first frequency is likely the stretch and the rest are the translation and rotational (or wag) modes of the CO molecule. The f/i indicates that the frequency is imaginary, corresponding to an unstable mode. With tighter convergence parameters and inclusion of the nearby surface atoms, you should see only positive modes for a well-converged state.

For dynamical calculation calculations using our vtstcode you can animate the modes (using the dymmodes2xyz.pl script). I'm not sure if this works with the built-in IBRION=5 approach. If not, a modified version should be fairly easy to construct.