My Community

dear all,
I try to calculate the binding energy of molecular oxygen with vasp.4.6 in the GGA (pw91) with the PAW-GGA potential tooken in the vasp library. my calculations leeds to a value of 6.68 eV largely overestimated with the experimental value of 5.2 eV.
my incar for oxygen atom is :
PREC = High
ISYM = 0 ! no symmetry
ISPIN = 2 ! allow for spin polarisation
VOSKOWN = 1 ! this is important, in particular for GGA
ISMEAR = 0 ! Gaussian smearing, otherwise negative occupancies
SIGMA = 0.1 ! intermid. smearing width
AMIX = 0.2 ! mixing set manually
BMIX = 0.0001
NELM = 20 ! 20 electronic steps
ICHARG = 1
IALGO=48
PREC = High
ENCUT = 400

for the oxygen dimmer the incar file is :

SYSTEM = O atom in a box
ISTART = 2
ISMEAR = 1 ! Gaussian smearing
SIGMA = 0.1
ENCUT = 400
ISPIN = 1
ISYM = 0
VOSKOWN = 1
IALGO=48
ISIF =2
IBRION = 1
NSW = 10
PREC = High


can any one help me to resolve this.

Thank for your time and your help.

1) for both, the molecule and the free atom, SIGMA is much too large, both, O and O2 have discrete levels in their electronic ground state configuration.
2) please also use Gaussian smearing for O2.
3) the ground state of O2 is the triplet state (ISPIN=2)
4) if you have not done so, please use the hard PPs

I was facing almost the same problem as matilda. A few questions:
1. I was using an ultrasoft GGA PP. How do I switch to the hard pp's.?

Thanks!

-Rahul

Hi, Hard PPs should be in the directory /element_h/POTCAR.Z.