A classification of covalent, ionic, and metallic solids based on the electron density.

Area of Science:

• Solid-state chemistry and materials science.
• Quantum chemistry and computational materials science.

Background:

• Crystalline materials exhibit diverse bonding types, crucial for their properties.
• Classical classification schemes, like van Arkel-Ketelaar diagrams, provide a framework for understanding these bonds.
• Electron density distribution within crystals contains comprehensive information about chemical bonding.

Purpose of the Study:

• To develop a novel, quantitative method for classifying crystal bonding types.
• To establish a classification system based on easily derivable properties of electron density.
• To compare the proposed classification with established models like the van Arkel-Ketelaar diagrams.

Main Methods:

• Calculation of three distinct indexes: flatness, charge transfer, and molecularity.
• Derivation of these indexes from experimental or theoretical electron density data.
• Application of the indexes to classify bonding types in various crystalline materials.

Main Results:

• The three proposed indexes (flatness, charge transfer, molecularity) are readily obtainable from electron density.
• The classification derived from these indexes closely resembles the established van Arkel-Ketelaar diagrams.
• This provides a robust, electron-density-based approach to bonding classification.

Conclusions:

• Electron density is a powerful descriptor for classifying crystal bonding.
• The proposed flatness, charge transfer, and molecularity indexes offer a quantitative and accurate alternative to classical methods.
• This approach facilitates a deeper understanding of chemical bonding in crystalline solids.