Adsorption is a kind of binding.

By "+ve" and "-ve" you apparently mean electron-volts (eV).

If the calculated Ead is negative, this means attraction (adsorption takes place). A positive Ead value means repulsion between the interacting components (no adsorption).

Adsorption is a kind of binding.

By "+ve" and "-ve" you apparently mean electron-volts (eV).

If the calculated Ead is negative, this means attraction (adsorption takes place). A positive Ead value means repulsion between the interacting components (no adsorption).

This is as like regular phenomena of enthalphy. That sign will indicate spontaneity of the adsorption process. though the adsorption energy might be little positive also possible.

I has a same opinion for Dr. Vladimir A. Basiuk and enhanced this opinion by the loading scheme.

Thank you everyone. I have few values which are slightly positive. In the order of 1-2 ev. So I must consider this as attraction or repulsion .

"Slightly" positive??? You must be joking! To begin with, eV units are good for band gap energies, etc.: for adsorption energies, chemists prefer kcal/mol. 1-2 eV = 23-46 kcal/mol: these absolute values are VERY high.

@Thank you Mr.Vladimir . I went through few more literature after your comment. In few paper eV is used and few other are using Kcal/Mol. the values for adsorption are in the order of -1 to -3ev . i have attached a reference paper. i am redoing the entire calculation to make sure i am not missing out in something .

Dear Somshekhar Puranmath,

I strongly suggest you to be more selective and critical:

(1) Pay attention whether the paper of interest is published in a good-quality, renown journal (definitely, not the paper you attached);

(2) Clearly distinguish between physical adsorption and formation of covalent bonds (it is the latter case which actually was "studied" in the paper attached);

(3) Even though the formation of covalent bonds is intended to study, be critical whether such a process is realistic (again, not the case: in the paper you attached, the authors substituted the edge H atoms with CO, CO2, NO and NH3, without explaining how this chemical process is possible at all);

(4) Even for realistic processes, please note that LDA and LSDA strongly overestimate binding energies;

(5) "It is conventionally accepted that the energetic threshold separating the binding energy of "physisorption" from that of "chemisorption" is about 0.5 eV per adsorbed species":

https://en.wikipedia.org/wiki/Chemisorption

(I gave you the link to Wikipedia, but you can consult this criterion in textbooks on physical chemistry).

So, unfortunately, you are missing many (including basic, conceptual) things.