  The coherence of an electronic spin in a semiconductor quantum dot decays due
to its interaction with the bath of nuclear spins in the surrounding isotopes.
This effect can be reduced by subjecting the system to an external magnetic
field and by applying optical pulses. By repeated pulses in long trains the
spin precession can be synchronized to the pulse period $T_\text{R}$. This
drives the nuclear spin bath into states far from equilibrium leading to
nuclear frequency focusing. In this paper, we use an efficient classical
approach introduced in Phys. Rev. B $\textbf{96}$, 054415 (2017) to describe
and to analyze this nuclear focusing. Its dependence on the effective bath size
and on the external magnetic field is elucidated in a comprehensive study. We
find that the characteristics of the pulse as well as the nuclear Zeeman effect
influence the behavior decisively.
