Search found 2255 matches

by graeme
Wed Apr 09, 2008 3:52 am
Forum: Bader
Topic: zero bader charge!
Replies: 4
Views: 51523

Re: zero bader charge!

You need to add core charges. See: http://theory.cm.utexas.edu/bader/vasp.php
by graeme
Tue Apr 08, 2008 3:03 pm
Forum: VTSTTools
Topic: NEB basic questions
Replies: 3
Views: 10710

Re: NEB basic questions

The images can become unequally spaced if you are using the climbing image. But if the saddle is between your widely spaced images, it sounds like something is wrong. Similarly for a linear band that converges right away - something is wrong. But I can't tell what's wrong without more information; i...
by graeme
Tue Apr 01, 2008 12:24 am
Forum: Bader
Topic: ECP in Gaussian and feature suggestion
Replies: 2
Views: 9524

Re: ECP in Gaussian and feature suggestion

We have struggled with a similar problem with pseudopotentials in VASP. The code can deal with this in a fairly simple way by associating each Bader volume with the nearest atomic center. But, if the charge density minimum between atoms is missing, there will be no maximum near atomic centers. In th...
by graeme
Wed Mar 19, 2008 2:11 am
Forum: Bader
Topic: For gga POTCAR
Replies: 1
Views: 6506

Re: For gga POTCAR

1. In order to get core charges, you need the latest version of vasp and must use the PAW potentials (which can be used with GGA). The core charges are not always essential, but it makes the analysis much better. 2. A good first guess is to use a grid that is twice as dense as the default value prin...
by graeme
Wed Mar 05, 2008 2:32 am
Forum: VTSTTools
Topic: error on website for dimer method
Replies: 3
Views: 8871

Re: error on website for dimer method

Ah, I think I see the problem. Let me summarize and try another modified description - the code is doing what I want it to do. if (FNr < FNMin): do not rotate, pass control back to the optimizer if (FNMin < FNr < FNMax): do at least 1 rotation if (FNr > FNMax): rotate until FNr<FNMax or the number o...
by graeme
Tue Mar 04, 2008 9:16 pm
Forum: VTSTTools
Topic: Dimer method - convergence criteria
Replies: 1
Views: 6724

Re: Dimer method - convergence criteria

This is a good point. The Dimer method uses a force criteria to quit, and does not demand that the minimum curvature be negative. To search for a saddle starting from a minimum, it is essential to perturb the system away from the minimum so that the forces are above the convergence criteria. If this...
by graeme
Sat Mar 01, 2008 4:39 pm
Forum: VTSTTools
Topic: error on website for dimer method
Replies: 3
Views: 8871

Re: error on website for dimer method

I guess I don't quite understand the issue - do you think that the Min/Max description in the variables is misleading, or are you saying that there is an error in the implementation? I've tried to clarify the variable descriptions: DFNMin: Magnitude of the rotational force below which rotation stops...
by graeme
Sat Mar 01, 2008 4:05 pm
Forum: VTSTTools
Topic: Interstitialcy mechanism
Replies: 2
Views: 7674

Re: Interstitialcy mechanism

Besides trying to determine a final state from your intuition about the reaction mechanism, you could either run dynamics at a high temperature to find nearby minima, or run min-mode following saddle point searches from your initial state.
by graeme
Sat Feb 23, 2008 3:36 pm
Forum: Bader
Topic: Can bader handle a molecule standing on the box edge?
Replies: 1
Views: 6498

Re: Can bader handle a molecule standing on the box edge?

It should be fine. We assume periodic boundary conditions in the analysis.
by graeme
Fri Feb 15, 2008 10:38 pm
Forum: Bader
Topic: RCORE vs MIN DIST
Replies: 12
Views: 27683

Re: RCORE vs MIN DIST

Ok, it's good that you are using the core charge. Now, what exactly are you concerned about: the difference in the V/Ti/Sc as you go from the _pv to _sv potentials (0.01-0.02 e), or that Rcore is less than Min Dist? If the former, I would suggest that this is related to the systematic error intrinsi...
by graeme
Fri Feb 15, 2008 9:01 pm
Forum: Bader
Topic: RCORE vs MIN DIST
Replies: 12
Views: 27683

Re: RCORE vs MIN DIST

It is now possible to write the core charges within vasp. This essentially eliminates the core charge problem. There are instructions about how to do this on the page http://theory.cm.utexas.edu/bader/vasp.php With core charges, the analysis should not be particularly sensitive to how many electrons...
by graeme
Fri Feb 15, 2008 6:46 am
Forum: VTSTTools
Topic: dimer method can not start.
Replies: 8
Views: 21783

Re: dimer method can not start.

Good to hear that this was solved. That run looks just fine.

Do you know why MPI_CHAIN was set in the makefile? Was this in one of the makefiles supplied by the vasp group?
by graeme
Sat Feb 02, 2008 6:38 am
Forum: VTSTTools
Topic: dimer method can not start.
Replies: 8
Views: 21783

Re: dimer method can not start.

I'm still not sure what's going wrong. Can you run a standard parallel vasp calculation, or a regular NEB run? You could try updating to the latest vasp.4.6.31 08Feb07, but I don't have any reason to believe that this will change anything. Are there any clues in the OUTCAR? Do you see a line with VT...
by graeme
Sat Feb 02, 2008 6:07 am
Forum: VTSTTools
Topic: about dynamical matrix calculation
Replies: 9
Views: 19874

Re: about dynamical matrix calculation

This is certainly slow convergence, but the numbers at this point look reasonable. As long as the 5th column remains negative, and forces (2nd column) remain small, it is likely near a saddle. Take a look at the XDATCAR (you can use xdat2xyz.pl to see a movie, or using vmd) to make sure that the geo...
by graeme
Fri Feb 01, 2008 6:06 pm
Forum: Bader
Topic: FFT grid
Replies: 3
Views: 11191

Re: FFT grid

There are two separate issues here. First, do the Bader charges converge with respect to the grid density. Second, do the results make sense. We would be concerned if the analysis does not converge. If you can not get well defined charges with a fine grid, that is a problem. If the results are not w...