Chemical interactions on oxigen clusters: role of the electron correlation and implications on high pressure phases

Abstract

Nowadays, solid oxygen under high pressure conditions is intensively studied in the theoretical and experimental community. The phase changes and the reasons of the modifications of the related physicochemical properties (magnetic behavior, Raman and IR frequency evolution with pressure, volume collapses, etc.) are still in need to be fully understood. Using monomer, dimer and tetramer units as system models to molecular condensed phases of oxygen, some of us have previously shown that the inclusion of electron correlation is determinant to reproduce experimental results. On this basis, the present work is devoted to the analysis of the chemical interactions in these oxygen clusters using highly correlated wave functions. We believe that a chemical bond analysis with high correlated wave-functions will deliver crucial information to better understand crystalline oxygen under high pressure conditions. The main task of this contribution is to study the chemical interactions in the framework of the Quantum Theory of Atoms in Molecules Analysis, Interacting Quantum Atoms Approach, and the Electron Localization Function (ELF) formalism with these correlated wave functions. Our analysis is important for solving important controversies related to this system: (i) is there or not a chemical bond between O2 units in the stabilization of oxygen crystalline structures at high pressure conditions?, (ii) explanation of the emergence of diamagnetic behavior in the ¿ phase, and (iii) understanding the ¿anomalous¿ evolution of Raman vibron frequencies with pressure. In addition, we present ELF patterns, and their progression with pressure, of calculated equilibrium structures of the ¿ phase of oxygen.