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1

Scripts, Tutorials and Applications / Re: Discrepancy in effective mass calculation in bulk silicon

« on: January 24, 2017, 09:39 »

Hi zh,

What I am confused about is not the difference in the bandstructure plots or the difference in curvature between MGGA and GGA. I do agree there will be some difference. What I don't understand is why the effective mass calculated from MGGA doesn't conform with the same bandstructure plot. From the above bulk silicon bandstructure plot there are three degenerate valence band. Two heavy hole bands which should have a mass higher than the light hole band. One can make this clever guess from the bandstructure plot but the mass calculated says otherwise (Heavy Hole: 0.327, 0.240  Light Hole: 0.270). This is what confuses me.

Thanks in advance,
Thomas

2

Scripts, Tutorials and Applications / Re: Discrepancy in effective mass calculation in bulk silicon

« on: January 23, 2017, 15:30 »

Hi Jess Wellendorff,

I did understand your point. But for the MGGA scenario why is one of the heavy hole mass (0.240) lighter than the light hole mass (0.270). This doesn't confirm with the bandstructure plot. At first glance from MGGA bandstructure, band curvatures for both heavy hole bands shows similar curvatures while the light hole band has a larger one. But the effective mass calculation doesn't conform with this.

Please find attached the bandstructure plot for bulk Silicon calculated using MGGA.

Thank you for your time and consideration,
Thomas

3

Scripts, Tutorials and Applications / Discrepancy in effective mass calculation in bulk silicon

« on: December 13, 2016, 10:46 »

Hi,

Why does the effective mass calculated using MGGA show a large variation with respect to GGA for the hole effective mass? I was under the impression that MGGA will not change the band curvatures in comparison to LDA and GGA functionals. Below is the extracted effective mass after DFT calculation using respective functionals.

Effective mass of bulk silicon(MGGA):
Electrons(longitudnal): 0.917    Heavy Hole: 0.327, 0.240  Light Hole: 0.270

Effective mass of bulk silicon(GGA):
Electrons(longitudnal): 0.911    Heavy Hole: 0.259, 0.257 Light Hole: 0.159

Please find attached the script that was used to generate the above said results. Please let me know if there are any mistakes in my script that raises this discrepancy.

Thanks in advance,
Thomas