The effect of hydrostatic pressure on a BaF2 crystal was studied within the shell model in the pairwise potential approximation. The structural phase transition from the cubic to orthorhombic phase was simulated. The behavior of the unit-cell parameters of the alpha- and beta-BaF2 phases under hydrostatic pressure (from 0 to 12 GPa) was investigated. The fundamental vibration frequencies of BaF2 under hydrostatic pressure (0-3.5 GPa) were calculated for both phases. The effect of chemical pressure on the BaF2 crystal was studied by simulating Ba1 - xMexF2 mixed crystals (Me = Ca, Sr). It was shown that at impurity concentrations up to 15-20 at. % the lattice constant varies in the same way as it does when hydrostatic pressure increases to P-c, which corresponds to a phase transition to the orthorhombic phase. The effect of chemical and hydrostatic pressure on BaF2 : Eu2+ doped crystals was also studied. The dependence of the absorption and luminescence zero-phonon line shift on the Eu2+-ligand distance was calculated. (C) 2002 MAIK "Nauka/Interperiodica".