On the theory of the orientational ordering of a solid orthohydrogen-parahydrogen mixtutre at zero temperature

The principle of stability of the ground state against elementary excitations is used in the axial model of quadrupolar systems (like solid mixture of ortho-para-hydrogen) to obtain the system of equations for order parameters, the number of metastable states and their average energy. The partition function of metastable states is obtained by means of averaging over the microcanonical distribution. The external field gradient is shown to induce the phase transition into quadrupolar glass phase.