UT theoretical chemistry code forum

Hello Prof. Henkelman and group

I am trying to find the TS of a hydride shift step on Al2O3. Initially, I started a NEB+climb calculation using a single k-point, iopt=3, default time step of 0.1. This calculation showed issues with force convergence; the forces were oscillating between 1 and 0.5 eV ...

Hello Dr. Henkelman

I have questions related to a couple of topics; one topic being TS_Extract.sh and the other being the DIMCAR file. The questions are as follows:

1) regarding the output displayed upon using TS_Extract.sh,
i) What does E-E0 mean? What value is chosen as E0?
ii) What exactly ...

Thanks for the explanation. That was helpful.

Thanks Dr. Graeme

while using the nebresults.pl script in one of my cases, I have found the following:

Forces and Energy:
0 0.019946 -1428.686600 0.000000
1 0.149487 -1428.505800 0.180800
2 0.234107 -1428.723800 -0.037200
3 0.089871 -1428.953500 -0.266900
4 0.071976 -1429.017500 -0.330900
5 ...

I see. Thanks. I have just tried doing this by running the following and I face an issue:

vfin.pl new_folder
cd new_folder
nebresults.pl

After using the command nebresults.pl, I get the following:
No OUTCAR in 00
Unzipping the OUTCARs....

Then, I use the command neb2dim.pl, and I get the ...

Also, another question related to the usage of neb2dim.pl:

Just to clarify, the usage of this script is as follows right:

neb2dim.pl (image no.)

where image no. is the image number of the highest energy image, and the above command has to be used in the directory where my NEB is, right ...

Thanks for the suggestions, Dr. Graeme. I will try them and let you know what I get.

I have a follow-up question, as you mention in the first paragraph that the calculations have both soft and stiff modes, how to check for the softness and stiffness of modes? I am unaware of the procedure and ...

Hello Dr. Henkelman

I am running a few climbing NEB calculations on ZrO2 and TiO2. Although the NEB profiles look fine in terms of change in slope, I see that they are converging pretty slowly. I have tried both iopt=2 and iopt=3, but I don't see any improvement. I use a ediif of e-06 and edifg of ...

Hello Dr. Henkelman

I have redone the vib freq. calculation with a potim of 0.002 Ang and ediff of e-07 and I see that the additional imaginary frequencies are going away. Also, having a NELM value higher than 150 or 200 helps. Thanks a lot.

Thanks Dr. Henkelman. Yes, I do see imaginary frequencies in the final state in the case of TS1 and TS3, but not in TS2.

Just a follow-up question, by any chance is there a way (theory,/thumb-rule/heuristic) to estimate the stiffness of a mode and choose a corresponding/specific potim/displacement ...

Thanks, Dr. Henkelman for the suggestion. I will change the optimizer and nelm and get back to you.

Just a follow-up question, in the files that I have sent, I see that the number of electronic iterations exceeds the maximum number only in the case of TS2_dimer_e-08, and in the other TS cases(TS1 ...

Hello Dr. Henkelman

I lowered the displacement to 0.002 Angstrom in the above-discussed example and I see that the 2nd imaginary frequency disappeared. Thanks for the suggestion.

I have tried the same idea of lowering the displacement to 0.002 Angstrom in other dimer calculations(which also have ...

Thanks, Dr. Henkelman.

Hello Dr. Graeme

I am using CI-NEB with IOPT=3 (QM method) option to obtain a TS. After my NEB converges, is it okay to directly proceed and check for the imaginary frequency in the highest energy image of the profile (or) is it important to further continue this NEB calculation by changing the ...

Thank you, Dr. Graeme

I have tried using perturbation theory and VASP throws this warning saying that perturbation theory cannot be used for DFT+D calculations. I currently use VASP 5.4.1 and use the PBE+D3 setting for my calculations. I am not sure whether there is a way to make this perturbation ...