I am trying to do calculations on adsorptions of singlet and triplet oxygen molecule on a Cu(100) surface? Apart from the ISPIN tag in INCAR, does VASP allow you to specify either triplet or singlet states? So far, my results do not change when I change the values of ISPIN. If no, any other software can do that?
ISPIN=2 #spin polarized calculation (2-yes 1-no)
NUPDOWN=0 #fix spin moment to specified value
# 0: S=0, 2S+1 = 1, SINGLET
# 1: S=1/2, 2S+1 = 2, DOUBLET
# 2: S=1, 2S+1 = 3, TRIPLET
Hi,
You can surely try Gaussian 09, u can calculate a lot of stuffs regarding various multiplicities. You can not only determine the ground state, but also the energies of the excited states. In Gaussian the reference as well as the target state can be specified. Probably you can try GAMESS also. both these packages include programs that can handle correlations very well and can determine the energies more or less accurately.
I agree with Kapil that NUPDOWN is the way to go, but do read the caution statements about charge density in the VASP manual. It may be best to start in a fresh directory with only the four input files, so that VASP is forced to generate the initial guess with magnetic moment compatible with the NUPDOWN number.
ISPIN=2 #spin polarized calculation (2-yes 1-no)
NUPDOWN=0 #fix spin moment to specified value
# 0: S=0, 2S+1 = 1, SINGLET
# 1: S=1/2, 2S+1 = 2, DOUBLET
# 2: S=1, 2S+1 = 3, TRIPLET
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