Many-particle covalency, ionicity, and atomicity revisited for a few simple example molecules

TL;DR

This paper revisits the concepts of covalency, ionicity, and atomicity in simple molecules using an exact diagonalization ab initio approach, providing new insights into electron correlation and bonding characteristics.

Contribution

It introduces a rigorous method to analyze many-particle bonding factors and incorporates atomicity to improve physical interpretation of molecular bonds.

Findings

Accurate determination of covalency and ionicity factors.

Identification of atomicity as a key concept in bonding.

Improved understanding of electron localization in molecules.

Abstract

We analyze two-particle binding factors of H2, LiH, and HeH+ molecules/ions with the help of our original exact diagonalization ab intio (EDABI) approach. The interelectronic correlations are taken into account rigorously within the second quantization scheme for restricted basis of renormalized single-particle wave functions, i.e., with their size readjusted in the correlated state. This allows us to determine the many-particle covalency and ionicity factors in a natural and intuitive manner in terms of the microscopic single-particle and interaction parameters, also determined within our method. We discuss the limitations of those basic characteristics and introduce the concept of atomicity, corresponding to the Mott and Hubbard criterion concerning localization threshold in many-particle systems. This addition introduces an atomic ingredient into the electron states and thus removes a spurious behavior of covalency with the increasing interatomic distance, as well as provides a more complete physical interpretation of bonding.