where x, y, and z axes are aligned to the principal axes of the ellipsoids, and m x, m y and m z are the inertial effective masses along these different axes. The offsets k 0, x, k 0, y, and k 0, z reflect that the conduction band minimum is no longer centered at zero wavevector. (These effective masses correspond to the principal components of the inertial effective mass tensor, described later.)