Anharmonicity of the lattice properties of strongly correlated ferromagnet UGe2

Based on ab initio calculations of the ground state energy as a function of volume E(V) and thermodynamic model of the crystal lattice, we study the role of phonon anharmonicity in the formation of a complex of thermal and elastic properties of UGe2. In the framework of the developed model, an explanation is given for the first time of the experimentally observed abnormal growth of the bulk modulus of UGe2 as a function of temperature. The reassessment of the lattice anharmonicity parameters led to an indication of a significant contribution of optical phonons to the thermal expansion coefficient (CTE) of UGe2, which has not been considered previously. Taking this contribution into account leads to the conclusion that there is a negative non-lattice component of the CTE not only in the region of magnetic ordering but also above the Curie temperature, which indicates the effects of short-range magnetic order.