[en] Analysis of calculation of crystal potential in SbSI ferroelectric semiconductor has been made. The results of SbSI band structure calculations performed by pseudopotential methods and by the method of linear combination of atomic orbitals were analysed. The Fourier series expansion of the crystal potential is carried out for SbSI. The conclusion is made on the dependence of the results obtained on the method of determination of the crystal potential. The Fourier series of the crystal potential are proposed to be found using an axpansion of the electron density in atoms over the Gauss functions that manes it possible to obtain integrals in an analytical form