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Cr dimer

Posted: Wed Oct 21, 2009 8:50 am
by rudra-b
Dear Colleagues,
while trying to get the AFM Ground state for Cr dimer (cluster) i am facing a great problem. My INCAR is:

Code: Select all

SYSTEM = Cr2

ISTART   =   1

LORBIT   =   11
EDIFF    =   0.0001
EDIFFG   =  -0.01

IBRION   =   1
NSW      =   100
POTIM    =   0.5

ISMEAR   =   0
SIGMA    =   0.01

ISPIN    =   2
VOSKOWN  =   1
MAGMOM   =  +6  -6

IALGO    =   48
LDIAG    =   .TRUE.
NELM     =  40
NELMIN   =   4
NELMDL   =   -5

#-------------    save memory--------------
ISYM     =    0
LCHARG   =  .FALSE.
LELF     =  .FALSE.
LWAVE    =  .TRUE.
and POSCAR is:

Code: Select all

Cr2
    1.000000000000000
    14.0000000000000000    0.0000000000000000    0.0000000000000000
     0.0000000000000000   14.0000000000000000    0.0000000000000000
     0.0000000000000000    0.0000000000000000   14.0000000000000000
   2
C
 6.0 7.0 7.0
 8.0 7.0 7.0
using PAW_GGA, and gamma point, I can not found the local magmom and ground state bond lenth as is previously reported.
Can you plz specify where the error is?
(I also tried optimization witout LORBIT and the static run using RWIGS, with no difference)

Cr dimer

Posted: Tue Oct 27, 2009 11:53 am
by rudra-b
anyone here to reply?

Cr dimer

Posted: Fri Jan 08, 2010 2:34 am
by jlrch
Although Cr2 is a very subtle system for the majority of electronic structure codes, VASP gives a reasonable solution at the GGA level, consisting a collinear AFM configuration at the very short distance of 1.5 A and having sizeable local magnetic moments of the order of 1.5 Bohr magnetons at each atom. Concerning your INCAR file, I suggest you to use Normal precision, increasing the plane-wave cutoff energy to 1.5 * ENMAX, reducing EDIFF to 1.0e-6, and increasing SIGMA to something more reasonable like SIGMA=0.1 eV. Be aware that convergence is very slow, so, increasing NELM to 250 and NSW to 50 would be appropriate.