I have found the band structure of MAPbI3 using VASP. And calculated 2nd derivatives of both VBM and CBM. And I calculated the effective mass by m*=square of reduced plank constant/Second derivative of E with respect to K.
For the above calculation I only consider the near points around VBM and CBM. Finally , my observed effective masses for holes and electrons are 0.000284m0 and 0.000774m0 .But these are very low compared to results of the other researches.
I need to know how to calculate effective masses using E-K diagram.I have attached the E-K diagram and also second derivative graph here.
In general, the effective mass has a tensor form. I typically calculate this tensor using a 3-or 5-point method for the derivatives around the VBM and CBM.
Take a look at emc code, I think this would clear up how to compute the effective masses https://github.com/afonari/emc
If you want to calculate the effective mass manually, you need to select a narrow region around CBM VBM, and then interpolate it using polynomial function for example (which I didn't see in the excel file), make sure you interpolate the bands in the 3 direction (if there is anisotropy) which is the case for MAPI.
much better way is to use a tool for that, since MAPI is a complicated example due to bands degeneracy.
In this recent example, they calculate the effective mass in MAPI.
https://nbviewer.jupyter.org/github/lucydot/effmass/blob/master/paper/notebook.ipynb
https://pypi.org/project/effmass/
Regards.
Tayeb.
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