[Pw_forum] Binding Energy for H2O with PAW

[Felix Brockherde]

Dear all,

We would like to calculate the binding energy for non-equilibrium H2O
geometries with PAW pseudo potentials.

The initial thought was to calculate the single-atom energies. However, for
H the system becomes metallic. We used smearing but the results seem too
far from the experimental value for us to use them (-0.91784682 Ry).

Now, we would like to calculate the binding energy by separating the H2O
molecule as far as necessary. We would thus avoid inaccuracies caused by
smearing because it is not a metallic system. However, when pulling H2O
apart, the DFT calculations do not converge.

Can anybody help with either how to get the separated H2O converged or a
different approach to get the binding energy with PAW pseudo potentials?

We used PWSCF v.5.1.1 and I attached an input file where QE does not
converge.

Best regards,
Felix Brockherde
TU Berlin

 &CONTROL
    calculation = 'scf',
    wfcdir = 'tmp',
    pseudo_dir = '/home/user/pseudo_potentials',
    tprnfor = .true.,
    prefix = 'prefix',
    tstress = .false.,
    outdir = './',
    wf_collect = .true.,
 /
 &SYSTEM
    nat = 3,
    ntyp = 2,
    ecutwfc = 90,
    ecutrho = 360,
    celldm(1) = 30,
    ibrav = 1,
 /
 &ELECTRONS
 /
ATOMIC_SPECIES
    H 1.00794 H_pbe-kjpaw_psl.0.1.UPF
    O 15.9994 O_pbe-kjpaw_psl.0.1.UPF
ATOMIC_POSITIONS alat
    O 0.5 0.3 0.5
    H 0.5 0.7 0.3
    H 0.5 0.7 0.7
K_POINTS automatic
   1 1 1   0 0 0
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