[Pw_forum] Hydrogen dissociation test

[Green Power]

Hi, All,
I wonder how to do broken symmetry calculations for a hydrogen molecule with
a separation larger than 3.0 a.u. using pw.x code. As I understand,  the in
the region larger then 3.0 a.u. separation, the restricted wavefountion
method, for instance the RHF, would fail, and UHF method or correlation
method is needed. I don't know how to break the symmetry of alpha spin and
beta spin using pw.x code. I tried to do that by spin-polarized calculations
using the following input. The energy is 0.05 a.u.lower than the
sipn-unpolarized method at he hydrogen separation of 2.4333672 angstom. But
at the sepration of 2.0100254, the spin-polarized method gave much energy
then sipn-unpolarized. Could you please check my input file? Mabye I have
smething wrong.

Another question is about the binding energy of hydrgen molecule. I
calculated the total engergy of H2 at 0.74 angstrom bond distanced and the
energy H atom, and comapred the energy difference, I got a binding energy
much higher than the experimental value of 436 kj/mol. I guess I did not
calculate the energy of Hydrogen atom properly. Could you give me any
suggestion how to do that?
Thank you.

Qian


*INPUT: Spin-polarized calculation*
&control
/
&system
    ibrav              = 1
    celldm(1)       = 30.0
    nat                = 2
    ntyp              = 1
    nosym=.true.,
    starting_magnetization(1)=1.0
    nspin =2
    ecutwfc         = 60.0
    occupations = 'smearing'
    degauss = 0.01
    smearing = 'gaussian'
/
&electrons
    conv_thr        = 1.0d-8
/
ATOMIC_SPECIES
    H   1.00    H.vbc.UPF
ATOMIC_POSITIONS {angstrom}
   H   0.0             0.0    0.0
   H   2.4333672   0.0   0.0
K_POINTS  AUTOMATIC
1   1   1   0   0   0
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090216/aa410663/attachment.htm