[Pw_forum] PBE0 in PWSCF
Stefano de Gironcoli
degironc at sissa.it
Fri Mar 6 17:29:58 CET 2009
I reproduce here the answer I gave privately ... just not to let a
thread without reply in the forum...
Dear Xinzheng Li,
the "total energy" should be the right number to look at...
it is actually:
one-electron contribution + hartree contribution + xc contribution
+ ewald contribution - Fock energy 1 + Half Fock energy 2
In the Harris Foulkes estimate the Fock energyes are not properly
accounted...
I'll correct this information. Thank you for the report.
regards,
stefano
xinzheng li wrote:
> Dear friends,
>
> My name is Xinzheng Li. I am a postdoc in University College London. I
> am using PWSCF to perform some PBE0 calculations for water cluster on
> metal surface recently. In order to make sure that the PBE0 number I got
> from PWSCF is correct. I performed a test for the binding energy of a
> water-dimer in gas phase (total energy of 2 water moleculars minus the
> total energy of a water dimer) taking the all-electron PBE0 results from
> Gaussian03 as reference. The converged binding energy from Gaussian03
> is around 207 meV. While after PBE0 calculation of PWSCF is performed, I
> have these lines in the output file:
>
> ! total energy = -68.48225787 Ry
> Harris-Foulkes estimate = -72.38797788 Ry
> estimated scf accuracy < 0.00000008 Ry
>
> The total energy is the sum of the following terms:
>
> one-electron contribution = -144.72933450 Ry
> hartree contribution = 71.54274579 Ry
> xc contribution = -12.87564636 Ry
> ewald contribution = 13.67425725 Ry
> Fock energy 1 = -7.81160613 Ry
> Fock energy 2 = -7.81177236 Ry
> Half Fock energy 2 = -3.90588618 Ry
>
> I have two questions about this output:
>
> 1. Shall I take the '! total energy' as the final total energy, or the
> 'Harris-Foulkes estimate' as the final total energy? For the comment:
> 'The total energy is the sum of the following terms', if I sum the
> numbers below, I don't get either 'Harris-Foulkes estimeate', or '!
> total energy'. Only if I sum the one-electron contribution, hartree
> contibution, xc contribution and the ewald contribution, can I get the
> 'Harris-Foulkes estimate'. Does it mean that I should take
> 'Harris-Foulkes estimate' as the final energy? If so, what is the
> meaning of the '! total energy'?
>
> 3. If I take Harris-Foulke estimate' as the total energy, the binding
> energy I get is 184 meV. If I take '! total energy' as total energy, the
> binding energy is 158 meV. Both of these two number are > 20 meV from
> the Gaussian all-electron benchmark. What is the expectation for the
> accuracy of such a value in the PWSCF code compared with all-electron
> Gaussian (when pseudopotentials, and supercell-size convergence are
> well-tested)?
>
> Thanks a lot for your patiency in advance!
>
> Sincere
> Xinzheng
>
>
>
> -----------------------------------------------------------------
> Dr. Xinzheng Li
> London Centre for Nanotechnology, University College London
> 17-19 Gordon Street, London WC1H, 0AH
> ucanxli at ucl.ac.uk
> ------------------------------------------------------------------
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