### Two imaginary vib modes for TS

Posted:

**Fri Oct 30, 2020 4:10 pm**Hello Graeme and Andri,

Hope you are doing well!

I am trying to find the vib modes for a possible TS (CH3CHCOOH to CH3CCOOH) of dehydrogenation. The surface is a Ni[111] 5 layers and bottom two constrained. I obtained the saddle point from NEB followed by dimer calculations. The forces on the dimer was converged to EDIFFG = -0.001. I initially started the dynamical matrix calculation with displacements only for the molecule on the surface (see attached files). I was testing for convergence w.r.t finite diff displacements of 0.005 and 0.0025. But I stopped because in both cases, there are two imaginary frequencies. I see this in other saddle points pertaining to other elementary steps too. Either I am consistently making a mistake or missing something. More info: ISYM=0; used dymseld.pl with initial and saddle point POSCAR to set up DISPLACECAR. POSCAR contains the saddle point. Kindly let me know if there's a way to share these files. Your opinions and suggestions will be highly important. Thank you.

Regards,

Keerthan.

Hope you are doing well!

I am trying to find the vib modes for a possible TS (CH3CHCOOH to CH3CCOOH) of dehydrogenation. The surface is a Ni[111] 5 layers and bottom two constrained. I obtained the saddle point from NEB followed by dimer calculations. The forces on the dimer was converged to EDIFFG = -0.001. I initially started the dynamical matrix calculation with displacements only for the molecule on the surface (see attached files). I was testing for convergence w.r.t finite diff displacements of 0.005 and 0.0025. But I stopped because in both cases, there are two imaginary frequencies. I see this in other saddle points pertaining to other elementary steps too. Either I am consistently making a mistake or missing something. More info: ISYM=0; used dymseld.pl with initial and saddle point POSCAR to set up DISPLACECAR. POSCAR contains the saddle point. Kindly let me know if there's a way to share these files. Your opinions and suggestions will be highly important. Thank you.

Regards,

Keerthan.