On the Prospect of Chemically Transferable Coarse-Grained Electronic Models for Soft Materials

Electronic coarse-graining (ECG) methods predict quantum-mechanical electronic properties directly from coarse-grained (CG) molecular configurations, enabling electronic predictions at mesoscopic length scales. Here, we present a diagnostic assessment of the feasibility of chemically transferable ECG models at predicting the HOMO energy across a broad polymer-relevant chemical space using all-atom, united-atom, and Martini-scale representations. A fundamental challenge at the Martini resolution is the many-to-one mapping degeneracy, in which chemically distinct moieties map to identical bead sequences, precluding a one-to-one correspondence between bead coordinates and electronic properties. We demonstrate that our proposed Element-Count-Label (ECL) representation, which augments Martini beads with explicit stoichiometric data and reduces this representation degeneracy, significantly improves chemical generalization across diverse polymer chemistries. However, we show that the CG force field does not sample the same configurational distribution of local molecular structure as that underlying the DFT-parametrized ECG model, and that even with improved chemical resolution, the model cannot recover electronic property distributions that are absent from the configurational space sampled by the CG force field. These results demonstrate that chemically transferable ECG requires future Martini-like force fields to explicitly preserve quantum chemistry-compatible local molecular structure in addition to macroscopic thermodynamic and structural fidelity.