Many chemical phenomena are ultimately due to energy balances between atoms. In order to reach firm and clear conclusions one needs a reliable energy decomposition analysis (EDA). The Interacting Quantum Atoms (IQA) energy partitioning method is one of the most recent EDA methods. IQA is a topological energy partitioning that generates well-defined intra- and interatomic contributions, of steric, electrostatic or covalent (exchange) character. IQA has a minimal and powerful architecture and does not suffer from a number of conceptual and practical problems that plague the more traditional non-topological EDAs (Chem. Soc. Rev., 44 (2015) 3177).
For the first time, our manuscript reports on a protocol for using the IQA to understand polymorphism, which we apply to the three polymorphs of succinic acid (SA), including the unusual polymorph that was recently discovered serendipitously (CrystEngComm, 20 (2018) 3971). The many intra- and interatomic energy terms from the EDA scheme are processed using a new technique that we developed called the Relative Energy Gradient (REG) method, which clearly identifies the atoms and corresponding energetic terms that govern the behaviour of the total system, in a minimal and unbiased way.
succ REG SI