One-particle density matrices along the molecular bonds in linear molecules

The bonding in a number of σ-bonded diatomic and linear triatomic molecules is interpreted in terms of the one-particle density matrix (ODM) along the bond axis. Special attention is drawn to the off-diagonal contributions of the ODM in a two-dimensional position space representation, which are shown to be indicative of a bonding or antibonding covalent interaction between the atomic centers.