2.1.2.1 Equation of Motion

The evolution of the quasi-momentum governed by the equation:

$$\frac{d\vec{k}}{dt}=\frac{1}{\hbar}\vec{F}(\vec{r},\vec{k},t),$$ (2.14)

where $\vec{F}(\vec{r},\vec{k},t)$ is an external force which has a spatial and a time dependence. This equation looks like Newton's law but the sense is quite different because now only external fields are considered. S. Smirnov: