COGITO: Extracting covalent bonds to rationalize crystal structure selection

Although covalent bonds are fundamental concepts in materials chemistry, directly extracting covalent bonds from quantum-mechanical methods like density functional theory (DFT) has been a longstanding challenge. A primary challenge has been relating the reciprocal-space electronic structure back to our more intuitive understanding of real-space bonding. Here, we present our toolkit Crystal Orbital Guided Iteration To atomic-Orbital (COGITO), a DFT post-processing tool that extracts real-space covalent bonds by systematically mapping the plane-wave solutions to nonorthogonal atomic-orbital tight binding model. With COGITO, we can holistically assess atomic and bond contributions to the electron density, magnetism, and electronic band energies. Using this tool, we rationalize why certain electrostatically unfavorable crystal structures (high Madelung energy) form due to unusually strong and directional covalent bond interactions. By unveiling the intricate covalent interactions in complex materials, COGITO facilitates the targeted design of materials with unconventional bonding and superior functional properties.