Accurate numerical evaluation of systematics in the experiment for electron electric dipole moment measurement in HfF${}^{+}$

Hyperfine structure of the ground rotational level of the metastable ${}^3{\mathrm{\Delta }}_1$ electronic state of ${}^{180}$HfF${}^{+}$ ion is calculated at presence of variable external electric and magnetic fields. Calculations are required for analysis of systematic effects in experiment for electron electric dipole moment ($e$EDM) search. Different perturbations in molecular spectra important for $e$EDM spectroscopy are taken into account.