Query on hydrogen adsorption energy

[surinder]

Hi everyone,

I am performing the calculations of reported literature work to learn VASP. I am studying the adsorption of a hydrogen atom on a two-dimensional sheet using VASP. To compute hydrogen adsorption energy following equation is used

Eads = E(sheet+Hatom) - E(sheet) -1/2 E(Hmolecule)

where
E(sheet+Hatom) = Energy of the sheet with an adsorbed hydrogen atom
E(sheet) = Energy of sheet
E(Hmolecule) = Energy of hydrogen molecule

The value comes out to be ~-2.67 eV which is very high, I think, to consider it as a good catalyst in hydrogen evolution reaction.

Relaxation of sheet with and without hydrogen atom is performed by using INCAR:

PREC = Accurate
ISTART = 0
ICHARG = 2
ENCUT = 500
IBRION = 1
EDIFF = 0.00000001
EDIFFG = -0.0001
NSW = 100
ISIF = 2
ISMEAR = 0 ; SIGMA = 0.05
LREAL = Auto
ISPIN = 2


Please suggest if I am doing anything wrong in INCAR file.

Thanks in advance
Surinder

[martin.schlipf]

The INCAR file looks alright. You may want to specify the initial magnetic moment (setting MAGMOM). I don't know if you system is metallic or insulating (determines which ISMEAR to use).

The only other thing I can suggest is to carefully study size convergence. Does you energy change when you adjust the vacuum size?

[surinder]

Thank you for your kind reply and advice. First, I will carefully analyze the effect of vacuum size on energy as you suggested.


Thanks
Surinder