UT theoretical chemistry code forum

So as in the original post of this thread, I'm modeling oxygen vacancy diffusion in bulk oxide and tried to compute the pre-exponential and the energy barrier. The NEB part converged with forces less than 0.01 eV/A. However, when I computed the vibrational frequencies at the initial state, I obtaine...

Regarding computing the vibrational frequencies at the saddle point: Let's say that we are done with the NEB part and we obtained a saddle point configuration. Does one need first to minimize the energy of the saddle point configuration under periodic Boundary conditions before the setup of the dyna...

So I did a comparison between ISYM=0 and ISYM=2 for oxygen vacancy hop in ThO2. I considered both neutral vacancy (F-center) and doubly charged. In both cases I get exactly the same migration barrier n regardless of the symmetry parameter. May be this problem is not the best test!

Thank you for your reply. Indeed I used to use ISYM=2 due to memory limitation in my computational resources. Apparently it is a dangerous setting for the NEB calculations. Recently I expanded my memory resources and switched to ISYM=0. I'm running some tests now and will post the comparison in few ...

Hi,

I wonder if some body has tested the effect of allowing symmetry breaking (ISYM=0) on the result of CI-NEB calculations. The parameter is computationally more expensive than the default ISYM=2 and I'm curious to see if it has any effect on the computed barriers.