sadle point optimization problem

Message

rghomari · #1 Post by **rghomari** » Tue Sep 09, 2008 5:15 pm

Hi every one.
i want to study the mecanisme of hydrogenation of ethene on one layer of surface pt(111).
i used as methode to optimize the transition state (the NEB methode) but i find in the end of the run that the stucture is deformed (broken).
1) i prepare five directory (00 01 02 03 04 05) four image and i put in every one file POSCAR.
2) i fixed the position of atoms of reactant and product (directories 00 and 05)
3)my file INCAR is :
System=Nudged Elastic Band
IMAGE=4
SPRING=-5
NPAR=4
LPLANE=FALSE
PREC=Accurate
ALGO=very fast
ENCUT=400
EDIFFG=0.001
ISMEAR=0
NSW=20
IBRION=1
POTIM=0.5
LREAL=FALSE
Why is not work? can you help me please.
i use VASP version 4.6.34.
thank you.

#2 Post by **admin** » Wed Sep 10, 2008 9:30 am

dear colleague,
the INCAR you show is ok for an NEB run. Usually NEB is a very reliable method and works correctly in VASP. Please check from the POSCARS of 00 and 05 if the interpolation has been done between reasonable geometries::
if eg one atom is on opposite sides of the unit cell in 00 and 05, it is 'dragged' through the cell if you just interpolate the positions (eg from 0.01 --> 0.99), which is obviously something you don't want. If this is the case, please replace 0.99 by -0.01