[gpaw-users] Water dimer energy is computed wrong

[Ask Hjorth Larsen]

You need to divide by 27.211 to convert eV to Hartree, not multiply.  Also,
gpaw uses a different reference energy than nwchem so you cannot compare
total energies at all. Compare energy differences instead, e.g. H2O vs H2
and O2.



El dom., 27 ene. 2019 6:15, Yuri via gpaw-users <
gpaw-users at listserv.fysik.dtu.dk> escribió:

> I'm performing this computation:
>
>
> ---HPAW python---
>
> from gpaw import GPAW, PW
> import ase.io
>
> def ev2hartree(energy):
>      return 27.21138602*energy
>
> h2 = ase.io.read("H2O-dimer.xyz")
> h2.center(vacuum=2.5)
> h2.set_calculator(GPAW(mode='lcao', basis='dzp', txt='h2o-dimer.txt'))
> print(ev2hartree(h2.get_total_energy()))
>
>
> ---H2O-dimer.xyz---
>
> Water dimer
> O -1.456 0 0
> H -1.78607530591 -0.759608197739 -0.482062826151
> H -1.78607530591 0.759608197739 -0.482062826151
> O 1.456 0 0
> H 0.496537604394 0 0.0923857208542
> H 1.78845259152 0 0.903855922824
>
>
> It returns E=-758.3970356319126 H.
>
>
> This is different from E=-152.899572664521 H returned by this NWChem
> script:
>
> start oh-dat
>   echo
>   geometry noautoz units angstrom
>     load H2O-dimer.xyz
>   end
>   basis
>     * library aug-cc-pvdz
>   end
>   dft
>     odft
>     xc b3lyp
>   end
>   task dft energy
>
>
> And different from E=-152.89661481 H returned by this Erkale script:
>
> System H2O-dimer.xyz
> Method hyb_gga_xc_b3lyp
> Basis aug-cc-pVDZ
>
>
> I believe that the correct answer is E=-152.89... H
>
>
> What is wrong with the GPAW script?
>
> https://wiki.fysik.dtu.dk/gpaw/ says that lcao performs atom-centered
> computations. Why is the result different then?
>
>
> Yuri
>
>
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