### Modeling of matix isolated systems.

### D.S. Bezrukov

*Lomocosov Moscow State University, Faculty of Chemistry*

**Abstract:**

The report is devoted to a description of our group's research in the field of modeling matrix-isolated atoms and diaomic systems. At the beginning of the report, various objects are presented that are objects of study using the matrix isolation technique. Methods for calculating the internal energy of a system are then presented. Since the object being studied is systems with predominantly van der Waals interactions, various versions of the method of diatomic fragments in a molecule are an effective semi-empirical technique that allows one to obtain correct quantitative estimates. Next, we discuss quantum chemistry methods that make it possible to obtain these curves at a good level of accuracy. The contributions of many-particle interactions and methods for taking into account the energy of zero-point oscillations are discussed. The option of modifying the matrix-matrix interaction potentials is considered, which allows us to move on to quantitative modeling of the interaction of free energies of the crystalline body.

The main achievement of the group is a computational technique that makes it possible to determine the number of thermodynamically stable capture sites and their geometry. The method is based on thermodynamic analysis of a large canonical ensemble using “free energy”-“number of atoms” diagrams. Several examples of determining stable sites are shown, and the influence of matrix creation conditions on the relative amounts of populated sites is discussed. Using model Lennard-Jones potentials, an analysis of possible sites was carried out in a wide range of potential parameters.

The next part of the report is devoted to modeling various spectroscopic properties of matrix-isolated systems. Raman spectroscopy, electron absorption spectroscopy, EPR spectroscopy. Methods for calculating spectrum parameters and their shifts relative to gas-phase systems are shown, and how these data are used to validate the results obtained for determining the number of stable sites is shown.

The report then discusses the description of dynamic processes of atomic migration in noble gas matrices. The calculation methods we developed, being equipped with an apparatus for searching for transition states, made it possible to explain a number of barriers observed in experiment.

Finally, a description of some interesting unsolved problems in this area is presented.