POTCAR

[saswata]

I want to determine hydrogen molecule energy and for that I used my INCAR as given below----
SYSTEM = H
ISPIN = 2
ISTART = 0
NSW = 30
IBRION = 2
ENCUT = 400
EDIFF = 1E-04
EDIFFG = -.010
LORBIT = 10

and my POSCAR is given as below---
Simple H2 Cal
10.0
1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
2
Direct
0.50000000 0.50000000 0.50000000
0.47211655 0.57875093 0.48485025

I used K-mesh of 8,8,8 monk-horst pack.
Now when I used POTPAW POTCAR I got energy -6.676639 eV and total charges in the OUTCAR as
# of ion s p d tot
----------------------------------------
1 0.586 0.025 0.000 0.611
2 0.586 0.025 0.000 0.611
------------------------------------------------
tot 1.173 0.049 0.000 1.222
But instead of that when I used POTPAW_GGA the energy is -2.217402 eV and the total Charge in OUTCAR as
# of ion s p d tot
----------------------------------------
1 0.382 0.000 0.000 0.382
2 0.382 0.000 0.000 0.382
------------------------------------------------
tot 0.763 0.000 0.000 0.763

Total energy wont be equal in these two cases that I am sure,though the two energy must not differ that much.But I doubt about the charges in the OUTCAR for POTPAW_GGA case.I do think there must be something wrong.Can you please comment on this that where I have made the mistake?

[admin]

1) for a molecule in a box, use the Gamma point only.
2) the H2 molecule should be non magnetic.
(PAW-LDA and GGA give almost the same total energies and partial charges for non spin polarized H2 )
LDA: -6.678 , 0.611 electrons/H
GGA: -6.780, 0.638