# Effective Mass¶

EffectiveMass (block-type)

In a semi-conductor the mobility of electrons and holes is related to the curvature of the bands at the top of the valence band and the bottom of the conduction band. With the effective mass option, this curvature is obtained by numerical differentiation. The estimation is done with the specified step size, and twice the specified step size, and both results are printed to give a hint on the accuracy. By far the most convenient way to use this key is without specifying any subkeys.

EffectiveMass
StepSize step
NumAbove na
NumBelow nb
UniqueKPoints k1 k2 ...
End

StepSize
(Default: 1e-3) Size of the step taken in reciprocal space to perform the numerical differentiation.
NumAbove
(Default: 1) Number of bands to take into account above the Fermi level.
NumBelow
(Default: 1) Number of bands to take into account below the Fermi level.
UniqueKPoints
List of unique k-points where to print the effective mass. If this option is omitted, it will use the top of valence band and the bottom of the conduction band.