[Pw_forum] Bond dissociation energy of CO (gas-phase)

[Axel Kohlmeyer]

On 9/6/06, Ameya Joshi <ajoshi at mines.edu> wrote:
>
>
> Hi all,

hi!

> Most calculations overpredict the BDE  by almost 15 kcal/mol, while the one
> using the BLYP pseudo underpredicts it by 11.6 kcal/mol. The BDE obtained

one comment on this:
your table does not indicate, what plane wave cutoff you were using
for the different pseudopotentials. in the case of the norm-conserving
potentials, you used for BLYP, this makes a huge difference, as ~30Ry
are far from convergence for that type of pseudopotential.

generally, i would suggest checking for basis set convergence (i.e.
convergence with respect to ecutwfc) for all sets of psps. the same
goes for the box size dependence.

cheers,
   axel.

> using the pseudos included in example03 and that using the PZ (LDA) pseudo
> give the worst result (almost 40 kcal/mol too high). For reference, I have
> also included the value obtained by using CASTEP and the PW91 functional,
> which yields a value within 5 kcal/mol of the experimental value.
>
> I'd like to clarify that I am using the triplet states for both O and C in
> these calculations. I realize that there might be some errors in my input
> files, so include a typical input file towards the end of this mail. (the
> only change in the other files is the name of the pseudo)
>
> Finally, I'd like to share my ultimate motive behind these calculations -
> I'm looking to calculate the binding energies of small molecules on nickel
> surfaces. I find that in case of CO, the binding energy is lower by about 15
> kcal/mol - the same difference as the BDE - as compared to CASTEP. So my
> guess is that the absolute energy of CO molecule is not being calculated
> correctly with my current settings.
>
> Any thoughts will be appreciated. Also, I should add that I have browsed the
> archive carefully and found no reference to this or similar problems there,
> but apologize if I've missed any relevant information (in which case please
> give a pointer to that discussion thread).
>
> *********
> Input file
> *********
>
>
>
> &CONTROL
>
> calculation = "relax",
>
> prefix = "CO",
>
> pseudo_dir = "c:/Ameya/Espresso/espresso-3.1.1/pseudo",
>
> outdir = "c:/Ameya/Espresso/espresso-3.1.1/tmp",
>
> /
>
> &SYSTEM
>
> ibrav = 1,
>
> celldm(1) = 20.D0,
>
> nat = 2,
>
> ntyp = 2,
>
> ecutwfc = 29.105D0,
>
> ecutrho = 144.D0,
>
> /
>
> &ELECTRONS
>
> conv_thr = 1.D-7,
>
> mixing_beta = 0.7D0,
>
> /
>
> &IONS
>
> pot_extrapolation = "second_order",
>
> wfc_extrapolation = "second_order",
>
> /
>
> ATOMIC_SPECIES
>
> O 16.00 O.pbe-van_bm.UPF
>
> C 12.01 C.pbe-van_bm.UPF
>
> ATOMIC_POSITIONS {angstrom}
>
> C 0.000 0.0 0.000
>
> O 0.000 0.0 1.100
>
> K_POINTS {Gamma}
>
> *********
> End of Input file
> *********
>
>
> Ameya Joshi, Postdoc
> ----------------------------------------
> Chemical Engineering Department
> Colorado School of Mines
> Ph. (303)-273-3192
> ----------------------------------------
>


-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
  Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.