[Pw_forum] Binding Energy for H2O with PAW

[Ari P Seitsonen]

Dear Felix,

   Just a quick comment on PANG Rui's response: It is true that those 
approximations should be closer to the correct value, but at most only 
about 20-25 %; this is how much Hartree-Fock exchange is mixed to the GGA 
exchange. The correlation functional remains the same, so the "gain" might 
be even smaller. And not to mention the HUGE computational effort one 
would spend; in such cases plane wave basis set is not a good idea for an 
isolated water molecule, better would be a code based on localised basis 
sets.

   Just my small note.

     Greetings,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
     Ecole Normale Supérieure (ENS), Département de Chimie, Paris
     Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Fri, 26 Feb 2016, 庞瑞(PANG Rui) wrote:

> Dear Felix
> If I am correct, PBE contains self-interaction error, that means it may give a wrong number when you use it to calculate a single electron system such as hydrogen. Mayben you
> could try B3LYP or HSE.
> Best wishes
> 
> 
> 
> 
> 
> ------------------
> [viewfile?type=logo&domain=sustc.edu.cn]
>
>     庞瑞(PANG Rui)
> 
> South University of Science and Technology of China/Department of Physics
> 
> No.1088,Xueyuan Road, Shenzhen,Guangdong
> 
>  
>  
>  
> ------------------ Original ------------------
> From:  "Felix Brockherde"<fbrockherde at gmail.com>;
> Date:  Fri, Feb 26, 2016 09:31 PM
> To:  "Pw_forum"<Pw_forum at pwscf.org>;
> Subject:  [Pw_forum] Binding Energy for H2O with PAW
>  
> 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
> 
>