Wrong convergence

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Wrong convergence

Postby priya » Wed Sep 21, 2005 7:16 am

I am looking at the total energies for two systems. One has the ideal cubic perovskite geometry and the other has the atoms displaced from their ideal positions. When I run VASP I get the energy difference between the two structures to be 4 eV which I know is ridiculous. I expect the difference to be around 0.5 eV. There are no other warnings in the run. I guess I am converging to a local minima. How can I get around the problem? I tried changing the number of KPOINTS, but that did not help. I attach the INCAR file used.

ISMEAR = 0
SIGMA=0.001
PREC=ACC

ISTART=0
EDIFF=0.1E-5

NBANDS=120

NSW=20
IBRION=2
Last edited by priya on Wed Sep 21, 2005 7:16 am, edited 1 time in total.
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Wrong convergence

Postby admin » Wed Sep 21, 2005 2:57 pm

1) in principle, a starting geometry should be reasonable enough
to avoid getting trapped in a local minimum (unless you do a real
MD run at elevated T)
2) have a look whether the second geometry really is converged
(check the remaining forces in OUTCAR and check if the
converged geometry is reasonable) or whether the calculation
just stopped automatically after NSW steps.
in addition you could try/check the following:
3) set PREC = High (which is higher precision than accurate)
4) choose a different optimisation algorithm (IBRION = 1)
Last edited by admin on Wed Sep 21, 2005 2:57 pm, edited 1 time in total.
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