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
(<i>Chem.
Soc. Rev.</i>, <b>44</b> (2015) 3177).<div><br></div><div>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 (<i>CrystEngComm</i>, <b>20</b> (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. <br></div>
A relative energy gradient (REG) study of the planar and perpendicular torsional energy barriers in biphenyl
