Hi
in DFT calculations, after calculating the adsorption energy, in the absence of the solvent, is here any relationship between the range of the adsorption energy and the type of adsorption (physisorption, physiochemical sorption or chemisorption)?
And can the type of the adsorption, I mean covalent, van der Waals and etc. be determined using the range of adsorption energy?
I will be grateful if anyone answer me or introduce me a geed reference about this issue.
Bests
If you do not want to take apart your calculation to investiagate the individual terms, some thoughts:
1) The old thermodynamic approach: Classically, the differentiation between chemisorption and chemisorption was actually made just by the adsorption energy. The energy threshold between the types was often set in the range 0.5-1.0 eV for an adsorption with one atom making "the contact". This assignment was made before suitable computation was available so an "internal differentiation" could not be made.
2) The absolutely correct, but unhelpful approach: The Schrödinger equation in its exact form does not know differences between adsorption types, it knows only a wavefunction. The r-6 term which results from perturbation theory only is required in DFT since this part is cropped by the "incompleteness" of Exchange-Correlation functionals.
Due to the latter, it is difficult to differentiate, even if your DFT software lists the "regular" DFT energy and the correction separately since the XC energy still includes some vdW energy.
Thank you for your response dear Jürgen Weippert and Fatima Boukhlifi.
From the literature I understood that there's a relationship, but I wanted to know the accepted ranges for each interaction type. I mean what is the adsorption energy range for physiosorption and also chemisorption?
I know that lower energies are related to physical and higher one to chemical. But what are the exact ranges?
If you know any good references that this matter is mentioned in it, please introduce it to me.
Bests
There are no "exact ranges". As I said, for a single atom making the contact people have set the threshould somewhere in the range 0.5-1.0 eV. If you adsorb molecules, you will have to scale it up proportionally.
Any older surface science texbook should be useful for that.
There is relationship between the amount of adsorption energy and type of adsorption. The energy Depends upon the wave length of absorption . Shorter the wavelength, then energy will be more. Hence, UV region the absorption energy is higher than IR (Vibration energy) and NMR (radio frequency absorption ) lower absorption energy .
Madhukar Baburao Deshmukh This discussion is about molecule-on-solid ADsorption, not light ABsorption.
Zahra Mousavi, Statistically such a relationship can be tried to prove. The main problem, however, is a reliable value of adsorption energy, especially for liquid-solid adsorption. Is it then possible to rely on the D-R isotherm or DFT as a source to determine the adsorption energy? I doubt it.