[Pw_forum] binding energy of molecular oxygen

[Giuseppe Mattioli]

Dear Junxiang Chen
If you keep in mind that DFT-GGA is probably one of the less accurate  
ab-initio methods (also when you do your best), your result seems not  
to be "far from experiment value". I would rather write in a paper  
that such a result is "reasonably similar to the experimental  
value"...:-)
HTH

Giuseppe

Giuseppe Mattioli
ISM-CNR
Italy

Quoting Junxiang Chen <cjxxjc729 at gmail.com>:

> Dear all,
>
>
>
> The same problem as
> http://qe-forge.org/pipermail/pw_forum/2009-November/089525.html , the
> binding energy of detached O2 is 6.57eV, which is far from experiment value
> ( 5.12eV ), or 5.7eV in this page.
>
>
>
>
>
> Input file ( O2 ):
>
>
>
> &SYSTEM
>
>                        ibrav = 12,
>
>                    celldm(1) = 16.0348541363689,
>
>                    celldm(2) = 1.52752767,
>
>                    celldm(3) = 2.665651575,
>
>                    celldm(4) = -0.3273333438252,
>
>                          nat = 2,
>
>                         ntyp = 1,
>
>                      ecutwfc = 45,
>
>                      ecutrho = 400,
>
>                  occupations = 'smearing' ,
>
>                      degauss = 0.01,
>
>                     smearing = 'methfessel-paxton' ,
>
>                        nspin = 2,
>
>    starting_magnetization(1) = 1,
>
> /
>
> &ELECTRONS
>
>             electron_maxstep = 200,
>
>                     conv_thr = 1.D-6,
>
>                  mixing_beta = 0.4,
>
>                  mixing_mode = 'local-TF' ,
>
> /
>
> &IONS
>
>                 ion_dynamics = 'bfgs' ,
>
> /
>
> ATOMIC_SPECIES
>
>    O     15.9994      O.pbe-rrkjus.UPF
>
> ATOMIC_POSITIONS crystal
>
> O        0.217969593   0.389882242   0.401960243
>
> O        0.217971037   0.389881524   0.456565745
>
> K_POINTS automatic
>
>   5 5 2   0 0 0
>
>
>
>
>
> The binding energy is calculated by BE=EO2-2*EO* and BE=6.57eV
>
>
>
>
>
>
>
> Could anyone tells me what's wrong?
>
>
>
>
>
> -------------------------------------------------------
>
> Junxiang Chen
>
> Ph.D. candidate
>
> Department of chemistry and molecular
>
> Wuhan University
>
> Wuhan, China
>
> Email: cjxxjc729 at gmail.com <mailto:cjxxjc729 at gmail.com>
>
>
>
>
>
> -------------------------------------------------------
>
> Junxiang Chen
>
> Ph.D. candidate
>
> Department of chemistry and molecular
>
> Wuhan University
>
> Wuhan, China
>
> Email: cjxxjc729 at gmail.com
>
> QQ: 95508097


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    Giuseppe Mattioli
    CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
    v. Salaria Km 29,300 - C.P. 10
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