Natural\nFragment Bond Orbital Method for Interfragment\nBonding Interaction Analysis

A complex chemical system is often\nexamined based on their fragments,\nso fragment-based analysis is the key to chemical understanding. We\nreport the natural fragment bond orbital (NFBO) method for interfragment\nbonding interaction analysis, as an extension to the well-known natural\nbond orbital method. NFBOs together with their corresponding natural\nfragment hybrid orbitals (NFHOs) allow us to derive local bonding\nand antibonding orbitals among fragments from the delocalized canonical\nmolecular orbitals. In this paper, we provide the algorithm for finding\nNFBOs and showcase its application to several chemically interesting\nsystems featuring significant interfragment bonding interactions.\nThrough these examples, the NFBO method is shown to be a powerful\ntool with which to analyze the electronic structures of molecules\npossessing strong interfragment bonding interactions.