How Does Spin-Orbit Interaction Influence Effective Mass in Semiconductors?

[aaaa202]

Often I see people using an effective mass model to describe electrons in the bottom of the conduction band.
Spin orbit is then included as a perturbation in this effective mass model. But what is the justification for using this sort of model?
Would the correct way not be to start from the full k dot p equation with spin orbit included and then derive an effective mass model from this? My concern is due to the fact that I would expect the effective mass to be dependent on the spin orbit interaction, but maybe that is not true.
Also, what about external magnetic fields. Do these affect the effective mass?

 

[Dr Transport]

no and no, spin orbit and the magnetic field do not affect the effective mass in $\vec{k}\cdot\vec{p}$

 

[aaaa202]

Okay so when I write a Hamiltonian on the form:

H = p²/2m* + SO + MAGNETIC FIELD

Is this equivalent to starting from the k dot p method and applying second order perturbation theory? (as you do in the case where you want to derive the effective mass hamiltonian without the SO and magnetic field terms).