Dear all,
I have done an a.b.initio calculation "density of states" and found that my band gap decreases with substitution, while the lattice parameter deceases "experimentally" normaly it should increase according to the quantum confinement effects ! How to explain this behaviour, is there any other parameters that could explain this behavior, any explanation would help me, thank you in advance !
The details fo the quation is not enough
as type of the substitutional lattice in this case is affecting strongly on the result
calculatios according to quantum confinement will lead to a reduction of band gap in semiconductors which different from that of the experimental ewsults aince they the proces of bond lengh in solids have different apoach.
The increase of band gap in bulk semiconductors will experience due to the substitutional atomic type such as size or ionicity, in this case the lattice increase will follow by the decrease of energy gap and cice versa
will for theoretical calculations the process depend on quantum confinement. The increase of lattice parametee will result to incease of band gaps
for more details I suggest to see the following power point presentation
"Solid Surface and Nanoscale materials Structure"
Presentation · July 2016 with 117 Reads
DOI: 10.13140/RG.2.2.31947.59684
Charmo, University of Charmo, University of Salahaddin, DOI:10.13140/RG.2.2.31947.59684
Cite this publication
Omar M S at Salahaddin University - Hawler, Arbil, Kurdistan, Iraq
Thank you so much Professor Omar M S for your explanation !
If any one does have any reference that explains the relation between impurity, lattice parameter and gap's energy ! I will appreciate that, i have found documentations but hey don't explain in details.
Impurity charges -> changes dielectric screening -> band gap renormalization and/or strain effects (simple guide)
What is the exact material system you are investigating? Does your system allow the presence of stable excitons?
Dear Alagu Thilagam, thank you for responding to my question.
I have a bulk spinel system AB2X4 where i substitute between A and A' non-magnetic elements (AA'B2X4, the lattice parameter and the band gap decrease linearly which is contradictory to literature. (there is excitons)
Hi Meriem, Issues still exist with DFT calc in solids, there is no "right" way to calculating the energy gap. Ab initio DFT calculation using a specific functional may not produce satisfactory results for band gap and lattice parameters at the same time. For example in semiconductors, lattice constants computed using LSDA yield reasonable results, but the same cannot be said for the band gap predictions. The (HSE) hybrid functional which incorporates a screened, short-range HF exchange can give reasonable predictions for both band gap and lattice parameters in the same run. Have you looked at the nature of the exchange interactions in the functional you have employed in your study. As you may know, the shifting of Fermi levels linked to electrons in the orbitals of "A" and "B" atoms may also influence changes in the band gap. I agree that there is an inverse relationship between band gap and lattice parameters (in general).
Dear Alagu i appreciate your response thank you!
And yes i did check on the exhange interactions of the system they do change from FM to AMF intercations with substitution.
Hi Meriem, Thats a positive developement, and I would be interested to know if excitonic effects dominate if you reduce the bulk spinel system to nanostructure forms.
Hi Alagu, i really don't know, but i will search for that !! thank you so much.
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