[Pw_forum] PBE0 in PWSCF

[Stefano de Gironcoli]

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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