Modeling of configurational transitions in atomic systems

Configurational transitions in atomic systems, i.e., transitions that change the system's geometric structure, include chemical reactions in gases, transitions between aggregate states of a polyatomic system, i.e., the phase transitions, and nanocatalytic processes. These transitions are analyzed from the standpoint of the behavior of the system on its effective potential energy surface (PES), so that the transition results from passage between different local minima of the PES. It is shown that the density functional theory (DFT) is suitable, in principle, for the analysis of complex atomic systems, but this method, being based on contemporary computer codes, is not suitable even for simple atomic systems, such as heavy atoms or metal clusters. Next, a statical determination of the energetic parameters of atomic systems does not allow analyzing the dynamics of configurational transitions; in particular, the activation energy of a chemical process differs significantly from the height of a potential barrier which separates the atomic configurations of the initial and final states of the transition. Notably, the static models, including DFT, give a melting point for clusters with a pairwise atomic interaction that is twice that from dynamic models which account for the thermal motion of atoms. Hence, the optimal description of configurational transitions for complex atomic systems may be based on joining the DFT methods for determining the PES of this system with molecular dynamics to account for the thermal motion of atoms.