Dear SK M ,

welcome,

In order to see electronic and energy interaction between two materials and the type of the junction formed between the two materials we look at the energy band diagram of the two materials referenced to the Vacuum.

The important energy levels are the electron affinity showing the position of the conduction band edge relative to the vacuum level.

Then comes the valence edge which is lower with than the conduction band edge by the energy gap.

The binding forces are electrostatic in nature and we have two see the possibility of forming electric field between the two materials.

This is dictated by the difference in the work function of the two materials.

Normally a dipole is formed at the surface which binds the two materials.

I think the binding is microscopic rather than macroscopic.

Best wishes

Abdelhalim abdelnaby Zekry Thank you Professor for the reply.

1. I have band-edge positions with reference to vacuum energy levels calculated for the 2D materials under the study. But the band edge positions of perovskite are taken from literature for comparing with band edge positions of the materials, to check feasibility of charge transfer. Your explanation about the role of CBM and VBM about electron affinity is not clear to me in reference to my query regarding binding energy being positive. (or even negative).

2. I am picking up the data for calculating the work function of the materials, to check the electric field formation and the polarity on the surface/s at the interface of perovskite and the material. This is another set of calculation.

So, from your reply, can i guess (as of now, because the work functions not yet calculated) that even though i get positive binding energy value w.r.t system energy difference (i.e. Total Energy minus individual material energies) still they could bound based on work functions?

After reading your reply, i got another question that if the binding between materials is dictated by work functions, then what information the values of the system difference binding energies i calculated would tell us?

Thanks a lot again for your above reply.

Regards.

Dear SK M ,

One must return to the definition of the binding energy between entities. The binding energy is the work done to separate the two entities from each other.

In this sense it is negative. Binding energy can not be positive. If it is positive it would mean that the entities can not bind to each other in the opposite they will escape from each other and try to keep themselves as far as possible from each other.

This means that the force between them will be repelling rather than attracting.

Best wishes

Abdelhalim abdelnaby Zekry Thank you professor. Exactly same i was thinking, it cannot be negative, if it's really a binding energy between the materials in question.

Incidentally, i have re-checked my calculation, and there was technical glitch and is fixed now. So, now I got negative value for binding energy. All good. Thanks again.

Regards

Dear SK M

Hope you are well!

Not at all. It is my pleasure!

would you please mark the answer as a best answer!

Best wishes