Degree of atomicity in the chemical bonding: Why to return to the H2 molecule?

TL;DR

This paper revisits the concept of atomicity in chemical bonds by analyzing the extit{H2} molecule with a novel approach, redefining covalency and ionicity, and introducing atomicity to better understand bond nature and localization.

Contribution

It introduces the concept of atomicity as a new characteristic in chemical bonding, addressing limitations of traditional covalency and ionicity factors using the EDABI method.

Findings

Redefinition of covalency and ionicity as functions of interatomic distance

Introduction of atomicity to describe localization in molecular states

Elimination of spurious behavior in covalency with increasing distance

Abstract

We analyze two-particle binding factors for the case of \ch{H2} molecule with the help of our original Exact Diagonalization \textit{Ab Intio} (EDABI) approach. Explicitly, we redefine the many-particle covalency and ionicity factors as a function of interatomic distance. Insufficiency of those basic characteristics is stressed and the concept of \textit{atomicity} is introduced and corresponds to the Mott and Hubbard criteria concerning the localization in many-particle systems. This additional characteristic introduces atomic ingredient into the essentially molecular states and thus eliminates a spurious behavior of the standard covalency factor with the increasing interatomic distance, as well as provides a physical reinterpretation of the chemical bond's nature.