Beyond electronic stabilization: towards a multicomponent conceptual density-functional theory for positron-driven...

Conventional bonding theory associates molecular stability with electronic energy lowering relative to separated fragments. While successful for ordinary molecules, this picture may fail when additional quantum particles contribute to stability. Here we construct a multicomponent conceptual density-functional theory (MC-CDFT) as the natural extension of conceptual DFT to multicomponent quantum systems. Starting from a constrained-search formulation of the multicomponent energy functional, we generalize conceptual DFT from scalar electronic descriptors to species-resolved vectors, matrices, and response kernels that explicitly encode intercomponent coupling. Within this framework, the bonding criterion is governed by the curvature of the total multicomponent energy functional, rather than by the sign of any isolated subsystem contribution. A bound minimum may therefore arise even when the electronic contribution alone is destabilizing, provided that intercomponent coupling compensates for this energetic penalty. Recent Quantum Monte Carlo results for the e⁺:Be₂ complex illustrate this mechanism: although the electronic contribution remains repulsive at all internuclear separations, the total multicomponent system remains bound [R. Porras-Roldan et al., Chem. Sci., 2025, 16, 22322-22332]. The present formulation provides a general conceptual framework for analyzing stability in multicomponent quantum systems in which more than one particle species contributes to bonding.