The structural, vibrational, and elastic properties of La2CuO4 are calculated using a model for calculating the energy of the crystal based on interionic potentials with the multiparticle Jahn-Teller contribution included explicitly. The microscopic reasons for the structural instability of the La2CuO4 lattice relative to rotations of the oxygen octahedra are investigated. A structural phase transition from the orthorhombic phase (space group D182h) into the tetragonal phase (space group D174h) under hydrostatic compression of an La2-xSrxCuO4 crystal is modeled. The (P,x) structural phase diagram for La2-xSrxCuO4 is constructed.