[QE-users] H2 molecule moves away from surface during relaxation

[Tamas Karpati]

It was just my guess that chemisorption would take place (i don't know
your materials).
If this is not the case, that is, you expect only physisorption (ie.
no dissociation) then
you are already there: 3 A indeed looks like a vdW complex (the adduct).

In this case try a few functionals with nonlocal terms and optimize QE
parameters
until a good enough match to experimental data is obtained. Otherwise
your geometry
will be unrealistic (eg. too long interatomic distances).
Dispersion is also important for chemisorption but without them your
vdW complex is not described well.


On Mon, Aug 31, 2020 at 7:33 PM Omer Mutasim <omermutasim at ymail.com> wrote:
>
> I have tried 1.5 A also, but it still moves away by more than 3 A.
> Do you mean H2 molecule will dissociate , so i have to study two H atoms adsorption instead of H2 molecule?
> Why should i pull one H ? What is the significance of local maxima of E ,,? Can you please elaborate
>
>  i want to study the perpendicular & parallel adsorption. Does that mean molecular H2 adsorption can’t tale place over Ni5P4 ?
> Regards
>
>
> Sent from Yahoo Mail for iPhone
>
> On Monday, August 31, 2020, 2:18 PM, Tamas Karpati <tkarpati at gmail.com> wrote:
>
> Hi,
> H2 was probably too close to the surface atoms. Try starting from ca.
> 1.5 A  which is closer to the both M-H bond lengths.
> It is probable that H2 will decompose without a barrier (ie. TS) in
> which case i recommend optimize the probable
> product (eg. Ni-H and P-H or what you see fit) then start pulling one
> H from the M (=either Ni or P) gradually and
> check what the other H does and whether or not you have a local
> maximum (ie a TS) on the E profile.
> HTH,
>   t
>
> On Sun, Aug 30, 2020 at 9:28 PM Omer Mutasim <omermutasim at ymail.com> wrote:
> >
> > Dear All
> > I’m studying perpendicular  adsorption of H2 molecule,  After relaxing H2 molecule + Ni5P4 slab , i found that H2 molecule moved away from the surface by 3 Angstrom, initially it was 1 A far from surface
> > Any explanation for this ?
> >
> >
> > Sent from Yahoo Mail for iPhone
>
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