Phase transitions and adjacent phenomena in simple atomic systems

Clusters and bulk systems of bound atoms with pair- wise interactions have two types ofexcitations: configurational, due to a change in the atomic arrangement in space, and thermal, associated with atomic vibrations. The configura- tional excitation is responsible for phase transitions in such systems and can be considered as a transition from the global minimum of the atomic potential energy surface in a multidi- mensional space of atomic coordinates to some other, higher- energy local minima. From this standpoint, various aspects of aggregate states of atomic clusters are considered, including coexistence of the liquid and solid cluster phases, the freezing pointasthetemperatureoftransitionfromthemetastableliquid state to the unstable state, the glassy states as unstable config- urationally excited states with long lifetimes, and the phase transition under high pressures when the crystal lattice for the distribution of atoms is no longer the most stable form for the solid state. The concept of voids as elementary internal config- urationalexcitationsofamacroscopicatomicsystem,whichare connected with local minima of the potential energy surface, allows us to consider the glassy-solid transition and processes of the growth of nuclei of a new phase as a result of void transport. The degrees of deviation from traditional macro- scopic thermodynamics for clusters and bulk systems near a phase transition is analyzed. It is shown that the thermal mo- tion of atoms makes a significant contribution to the entropy jump at the phase transition, which allows us to use the Linde- mann criterion for the phase transition and other criteria which use parameters of thermal motion of atoms, even though the inherent nature of the phase transition is determined by config- urational excitation.