Quantum Mechanics Enables "Freedom of Design" in Molecular Property Space

Rational design of molecules with targeted properties requires understanding quantum-mechanical (QM) structure-property/property-property relationships (SPR/PPR) across chemical compound space. We analyze these relationships using the QM7-X dataset---which includes multiple QM properties for ~4.2 M equilibrium and non-equilibrium structures of small (primarily organic) molecules. Instead of providing simple SPR/PPR that strictly follow physicochemical intuition, our analysis uncovers substantial flexibility in molecular property space (MPS) when searching for a single molecule with a desired pair of QM properties or distinct molecules with a targeted set of QM properties. As proof-of-concept, we used Pareto multi-property optimization to search for the most promising (i.e., highly polarizable and electrically stable) molecules for polymeric battery materials; without prior knowledge of this complex manifold of MPS, Pareto front analysis reflected this intrinsic flexibility and identified small directed structural/compositional changes that simultaneously optimize these properties. Our analysis of such extensive QM property data provides compelling evidence for an intrinsic “freedom of design” in MPS, and indicates that rational design of molecules with a diverse array of targeted QM properties is quite feasible.