about the determination of the transition state
Posted: Fri Jun 23, 2017 1:05 pm
Hello everyone,
I am a beginner user of VTST. I'm looking for TS of interstitial in fcc systems.
To determine in one simulation the migration energy and the transition state I used vasp compiled with vtst.
I used 2 optimizers FIRE and LBFGS. Both simulations converged to the minimization criterions specified (EDIFF=1e-5 and EDIFFG=-1E-2)
By plotting the MEP, the image with the highest energy was the TS.
But when I wanted to determine the Gvib (using phonopy) of the TS (to get the attempt frequency (..exp(-(Gvib(TS)-Gvib(ini))/kT)) I also plot the phonon band structure.
The problem is that the band-structure has not the characteristic of a TS (I had 2 imaginaries modes or zero imaginary mode).
You can find attached as support 2 plots and the NEB using FIRE optimizer for N diffusiong between tetra and M site in fcc.
So, here my questions :
Can vtst can failed to determine the TS when the path has some symmetries characteristics ?
Could it be that the NEB are not enough converged ? (EDIFFG = -1E-3 ?)
Maybe I could use improved dimer method or lanczos ? But I didn't find any practical examples in crystal so I not really sure how I should proceed.
Any suggestion are welcome, I'm quite stuck with it.
I am a beginner user of VTST. I'm looking for TS of interstitial in fcc systems.
To determine in one simulation the migration energy and the transition state I used vasp compiled with vtst.
I used 2 optimizers FIRE and LBFGS. Both simulations converged to the minimization criterions specified (EDIFF=1e-5 and EDIFFG=-1E-2)
By plotting the MEP, the image with the highest energy was the TS.
But when I wanted to determine the Gvib (using phonopy) of the TS (to get the attempt frequency (..exp(-(Gvib(TS)-Gvib(ini))/kT)) I also plot the phonon band structure.
The problem is that the band-structure has not the characteristic of a TS (I had 2 imaginaries modes or zero imaginary mode).
You can find attached as support 2 plots and the NEB using FIRE optimizer for N diffusiong between tetra and M site in fcc.
So, here my questions :
Can vtst can failed to determine the TS when the path has some symmetries characteristics ?
Could it be that the NEB are not enough converged ? (EDIFFG = -1E-3 ?)
Maybe I could use improved dimer method or lanczos ? But I didn't find any practical examples in crystal so I not really sure how I should proceed.
Any suggestion are welcome, I'm quite stuck with it.