Ground state and ordering of a quantum crystal in the case of a pseudospin <i>S</i> = 1

The structure of the ground state of a pseudospin system was studied in the molecular-field approximation taking into account tunneling. The case of a potential with three minima, corresponding to the pseudospin S = 1, and ferrodistortional ordering was studied. A first-order phase transition between the ordered and disordered phases at T = 0 was found. The possibility of the formation of a partially ordered antiisostructural phase, associated with tunneling, was studied. It was established that in the cases studied such a phase does not exist.

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