# Mean_free_path in Amset

Dear Alex and kind users,

I am wondering how does boundary scattering involve in the scattering rates? v_g/L in which v_g is the group velocity. How does code extract the v_g? Different k point has different v_g. Using gamma point? In the practical application, could we set the L is the sample length? Thanks a lot!

Best wishes,
Zhibin

Hi Zhibin,

The group velocity (v_\mathrm{g}) is obtained for each band and k-point on the dense mesh during Fourier interpolation. The band and k-dependent group velocities are primarily used to calculate mobility. For example see the first equation on the transport page.

L should be the grain size of your sample.

Best,
Alex

Dear Alex,

Thanks a lot for your kind explanation.

Best wishes,
Zhibin

Dear Alex,

Does this flag (mean_free_path) work in the version amset v0.4.5? I used 10 nm and 1nm for this grain size, the mobility did not change compared to the original situation (without setting mean_free_path). Could you please give me some suggestions?
Thanks a lot!

Best wishes,
Zhibin

Hi Zhibin,

Yes this option should work. However, to include it you have to specify the MFP option in the scattering_type setting. E.g., scattering_type: ["ADP", "POP", "IMP", "MFP"].

Apologies for the confusion.

Best,
Alex

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Dear Alex,

Thanks a lot for your kind reminder. I made the mistake to overlook that flag.

Best wishes,
Zhibin

Dear Alex and kind users,

In the experiment, if I get a single crystal material, for example, I have MoS2. The whole sample is 14 micrometer, is there any possible having a grain boundary scattering in it? Without boundary scattering, I obtained the mobility is around 10^4 cm^2/Vs at 10 K. But the measured data is around 100. I am very confused that what is the reason for this big gap between theory and experiment. I set: scattering_type: [IMP, ADP, POP, PIE]. However, when I added the boundary scattering in the amset, the data is reduced to around 500. I am wondering that what is the condition for adding the boundary scattering? My friends told me that a single crystal has no boundary scattering which only occurs at polycrystalline. Could you give me some suggestions?

Best wishes,
Zhibin