I calculated the band structure of O2 adsorbing in CH3NH3PbI3. I got the result as the following attach. who can tell me why it appear the fat band. anyone has suggestion?
Did you checked if the O2 is chemosorbed? If the oxygen molecules do not interact strongly with the other system its electronic levels do not depend on k and the oxygen bands are just horizontal lines.
hello,
Viorel Chihaia, you mean I can't consider the band of O2, If the O2 is physical adsorption?
I guess that you use a supercell to model the adsorption of O2 on CH3NH3PbI3. Therefore, in your calculations if the O2 is not strongly interacting with the host or with its image outside the cell (which is not the case as I guess that you are not interested in a periodic adsorption of O2), its level will give just a flat band. If the O2 is just physisorbed then you will have a flat band for oxygen.
yes, your guesses is right. The flat band is belong oxygen, because i have calculated of PDOS of adsorbed system.
Thank you for your answer.
Dear Sophia,
Adding to Viorel who gave a satisfactory answer, the energy band structure of pervoskite crystal should not contain any allowed energy levels in the energy gap. However, if the material is doped with low density impurities, allowed energy levels appear inside the energy gap. The position of the allowed state depends on the energy needed to transfer an electron from the impurity to the valence band. This is very known phenomena and is exploited for doping process.
Also, if you interrupt the periodicity of the crystal at its surface without adding any any impurities at that surface, also allowed energy state will appear near the middle of the energy gap. The density of such state can be varied by passivatation with atomic hydrogen or oxygen. But in this case it is a chemical rather than physical absorption.
Physical absorption may not affect appreciably the electronic states.
You can your self study all these cases.
wish you success
Thank you Abdelhalim Zekry,
In order to determine which type of adsorption, I make the difference charge density. Please see attachment. But I can't analysis the result, do you have any suggestion?
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