  As a well-established procedure for the vast majority of normal main-sequence
stars, determination of atmospheric and stellar parameters turns to be a
challenging process in case of magnetic chemically peculiar stars.
Inhomogeneous distribution of chemical elements and strong magnetic fields make
most of the standard photometric and spectroscopic calibrations inapplicable
for this class of stars. In this work we make use of available observed energy
distributions calibrated to absolute units, stellar parallaxes, high-resolution
spectroscopic observations, and advanced stellar atmosphere models to derive
parameters of three bright Ap stars: 33Lib, gammaEqu, and betaCrB. Model
atmospheres and fluxes were computed with the LLmodels code. Synth3 and
Synthmag codes were used to compute profiles of individual spectral lines
involved in abundance analysis. For each of the stars, we construct a
self-consistent atmospheric models assuming normal and depleted helium
compositions and derive empirically stratification profiles of certain
elements. The effective temperatures and surface gravities are found from the
simultaneous fit to spectroscopic, photometric, and spectrophotometric
observations calibrated to absolute units. We show that using advanced model
atmospheres and accurate stellar parallaxes allows one to derive stellar radii
with high accuracy, and these are consistent with those obtained from
independent but more complicated interferometric observations.
