Discrepancy between input and output Electronic Density

General discussion around the EPW software

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galfinit
Posts: 1
Joined: Thu Jan 23, 2025 2:28 pm
Affiliation: unimib Milan

Discrepancy between input and output Electronic Density

Post by galfinit »

Dear all,

In a mobility calculation, I set a specific carrier concentration (ncarrier), for example, -1.5E21(hole mobility). However, after the Progression iq (fine) step, the program prints the temperature, Fermi level, and hole density, but the reported hole density is 0.227147E+21 instead.

I would like to ask:

1) Which parameters could influence this discrepancy? I noticed that increasing fsthick and refining the grid does not significantly change the result.
2) Is the mobility result valid for the given output density, or should I disregard it completely?

Thank you in advance for your help!

Best regards,
Giuseppe
stiwari
Posts: 53
Joined: Mon Jun 26, 2023 9:48 pm
Affiliation: UT Austin

Re: Discrepancy between input and output Electronic Density

Post by stiwari »

Hi Giuseppe,

The Fermi-level is found by using a bisection method (iterative) since its a root-finding problem. However, there is an upper-bound to the number of iterations. That means, once the max number of iterations is reached and the relative error (which is 1e-5) between previous and current step is still higher than the threshold (which is 1e-5), the code returns the last computed Fermi-level along with the hole/electron density for that Fermi-level.

This rarely happens when carrier concentration is low but since your carrier concentration is quite high, it makes sense. Coming to your question 2, the mobility is valid for the carrier-concentration returned by EPW.

Best regards,
Sabya.
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