COGITO: A tool to unlock the chemistry in crystals after DFT calculations

Modern DFT methods produce precise electronic band structures without chemical intuition. Techniques used to uncover chemistry in crystals, such as Bader charge, LOBSTER, or using machine learning, often exhibit limitations in their ability to accurately partition the electron wavefunction, which impacts our ability to draw qualitative insights. Here we present a new algorithm, Crystal Orbital Guided Iteration To atomic-Orbital (COGITO), which systematically maps the DFT plane wave solutions to nonorthogonal atomic-orbital tight binding with a high level of accuracy. Using this tool, we obtain high quality atomic charges and crystal overlap Hamiltonian populations (COHP). But more importantly, COGITO opens the door to rigorously investigate more complex questions, such as: How do orbital radii, energies and crystal field-splitting change with different atomic coordination environments? How do individual bonds contribute to the band dispersion and total energy? Applying this method to chemically and intuitively explain electronic structures from DFT calculations allows us to holistically extract the chemical origins of optoelectronic and magnetic properties that derive from the electronic band structure.