all 0.0 forces from nebbarrier.pl

[rachelberk]

Hello,
I am running VASP 5.3.5 implemented with the VTST tools on NERSC and when I run the current version of nebbarrier.pl (downloaded yesterday from http://theory.cm.utexas.edu/vtsttools/scripts.html) I get all zero forces for the intermediate images in the neb.dat file:

0 0.000000 0.000000 -0.033023 0
1 1.885349 0.565354 0.000000 1
2 3.784811 0.306657 0.000000 2
3 5.576834 1.287476 0.000000 3
4 7.285078 0.084631 0.000000 4
5 8.857768 -0.286671 0.025546 5

I have traced this back to a difference in the OUTCAR file from NEBs I used to run with VASP 4.6.35 that had NEB sections looking like this:

--------------------------------------------------------------------------------------------------------


NEB: the previous image is higher in energy: F
NEB: the next image is higher in energy : T
NEB: only next energy greater

NEB: Tangent
----------------------------------------------
... (values for each atom in geometry) ...

NEB: forces: par spring, perp REAL, dneb 0.142174 0.267327 0.000000
NEB: distance to prev, next image, angle between 0.373571 0.402006 152.397069
NEB: projections on to tangent (spring, REAL) 0.142174 -0.376604

FORCES: max atom, RMS 0.100471 0.026954
FORCE total and by dimension 0.201706 0.098389


to the NEB section of the current OUTCARs that look like this:

--------------------------------------------------------------------------------------------------------


NEB: the previous image is higher in energy: F
NEB: the next image is higher in energy : F
NEB: image is at an extrema
NEB: diff energy (min, max): 2.013657 2.235832

NEB: Tangent
----------------------------------------------
... (values for each atom in geometry) ...

NEB: forces: par spring, perp REAL, dneb 1.373534 2.107970 0.000000
NEB: distance to prev, next image, angle between 1.776348 1.501642 112.783846
-1.373534 -1.133137
stress matrix after NEB project (eV)
0.00000 0.00000 0.00000
0.00000 0.00000 0.00000
0.00000 0.00000 0.00000
FORCES: max atom, RMS 1.600415 0.281295
FORCE total and by dimension 2.515975 1.374603
Stress total and by dimension 0.000000 0.000000

I see that the nebbarrier.pl script greps "NEB: projections" and reports the 2nd number as the force for each image, but the current OUTCAR does not have the NEB: projections line, therefore the forces in neb.dat are 0.000000. I am trying to figure out if this is (a) an issue with the incorporation of the VTST tools in VASP 5.3.5 on NERSC or (b) an intentional change in the VTST code that was not updated in the nebbarrier.pl script. By drawing a parallel between the two OUTCARs, the 2nd number in the line after the "NEB: distance ..." line looks promising for the image force, but I am hoping someone can speak definitively to this issue?

Thank you!

[graeme]

I'm puzzled by this problem. Looking at the vtstcode (TST: version 3.1), I see the following code which writes NEB data:

!======================================================================
! print neb information
!======================================================================

4696 format( /' NEB: Tangent'/ &
' ----------------------------------------------')
4697 format(/1x,'NEB: forces: par spring, perp REAL, dneb ',3f12.6)
4698 format(1x,'NEB: distance to prev, next image, angle between ',3f12.6)
4699 format(1x,'NEB: projections on to tangent (spring, REAL) ',2f12.6,/)

IF (iu6>=0) THEN
WRITE(iu6,4696)
WRITE(iu6,'(3F13.5)') (tangent(:,ni),ni=1,nions)
WRITE(iu6,4697) SQRT(SUM(f_spring_par**2)),SQRT(SUM(f_perp**2)),&
SQRT(SUM(f_dneb**2))
WRITE(iu6,4698) SQRT(SUM(dR_prev**2)),SQRT(SUM(dR_next**2)),&
acos(min(max(SUM(return_unit(dR_prev,nions)* &
return_unit(dR_next,nions)),-1._q),1._q))*180._q/PI
WRITE(iu6,4699) SUM(f_spring_par*tangent),SUM(f_par*tangent)
ENDIF


Based upon this, I don't see how the "NEB: forces:" and "NEB: distance" information is being written without the "NEB: projections" data.

Perhaps make sure that you have all the vtstscripts downloaded into a single directory; the scripts can call other scripts and need to be able to find them. I don't believe this is your problem, however, since you have shown that the information is not in the OUTCAR. Perhaps check the VTST version reported in the OUTCAR. If you can't get to the bottom of this, if you can post the input files, I can try to reproduce (and correct) the problem.

[rachelberk]

Thank you so much for your reply! Based on what you said it seemed like there was likely a problem with the implementation of the VTST on in VASP at NERSC. I worked with the admins there and we were able to fix the problem; the "NEB: projections" line is now printing correctly :) Thanks for your help with figuring this out!