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I want to calculate the binding energy of H2 dimmer, E, using PAW_PBE potential.
Obtained value seems to be rather large.
TOTEN(H2) = -6.687eV (H2 dimmer)
TOTEN(H) = +0.000854eV (H atom)
E=-(TOTEN(H2)-2*TOTEN(H)) = 6.68eV
bond length = 0.75102 A
The result using PAW_GGA potential was almost the same.

I found a paper (G. Kresse & J. Hafner, Surface Sci. 459 (2000) 287) in which E is calculated to be 4.58 eV using PAW_GGA potential.

What's wrong with my calculation?

I calculated total energies of H2 dimmer and H atom as follows:
----
used potential = PAW_PBE H 15Jun2001
used VASP version = vasp.4.6.28 25Jul05 complex
---- POSCAR for H2 dimmer
H2 molecule in a box
1.0 ! universal scaling parameters
8.0 0.0 0.0 ! lattice vector a(1)
0.0 8.0 0.0 ! lattice vector a(2)
0.0 0.0 8.0 ! lattice vector a(3)
2 ! number of atoms
cart ! positions in cartesian coordinates
0 0 0 ! first atom
0 0 0.5 ! second atom

---- INCAR for H2 dimmer
SYSTEM = H2 dimer in a box
ISMEAR = 0 ! Gaussian smearing
NSW = 5 ! 5 ionic steps
IBRION = 2 ! use the conjugate gradient algorithm
ENCUT = 350.0
POTIM = 0.1

---- POSCAR for H atom
H atom in a box
1.0 ! universal scaling parameters
7.0 0.0 0.0 ! lattice vector a(1)
0.0 8.0 0.0 ! lattice vector a(2)
0.0 0.0 9.0 ! lattice vector a(3)
1 ! number of atoms
cart ! positions in cartesian coordinates
0 0 0

---- INCAR for H atom
SYSTEM = H atom in a box
ISMEAR = 0 ! Gaussian smearing
SIGMA = 0.01
ENCUT = 350.0

Your results are very good:

please have a look at
G.Kresse, PRB 62, 8295 (2000) which presents an elaborate study of the dissocaiation of H2 (on the potential energy hypersurface) (p 8299, section B):
d_H2= 0.75 A
E_binding= -6.8 eV / molecule.

Thank you, Administrator.
After reading the paper [G.Kresse, PRB 62, 8295 (2000)], I found that the E_binding=-0.68eV corresponds to the energy for the dissociation of an H2 molecule to two H atoms at non-spin-polarized state.
When I calculate the “normal dissociation energy�, I should calculate the total energy of H atom at spin-polarized state.
I suppose that the total energy of spin-polarized H atom counts an interaction between spins of a H nucleus and an electron.

I recalculated the H2 binding energy:
TOTEN(H atom [spin-polarized])=-1.10351 eV
E_binding=-(TOTEN(H2)-2*TOTEN(H [spin-polarized ])) = 4.48eV