Characterizing off-diagonal regions of one-electron density matrix.

The off-diagonal regions of the one-electron density matrix (ODM) are characterized according to their contributions to the chemical bond. In particular, these regions of the ODM difference maps were used to characterize the chemical bond in various diatomic molecules. The nature of a critical point, core interaction critical point, in the off-diagonal part of ODM reveals the chemical bond type: maximum for covalent bond, minimum for closed-shell interaction, and saddle point for a charge-shift bond. [ABSTRACT FROM AUTHOR]