Martin Rahm

This contribution presents an Energy Decomposition Analysis (EDA) built from the Experimental Quantum Chemistry (EQC) framework. Departing from the original EQC partitioning, the EQC-EDA decomposes bond formation energies into orbital, charge-transfer, and electrostatic-reorganization terms, enabling more direct comparisons with conventional EDA methods. These terms can be further partitioned by fragment and into valence and core contributions, offering a complementary view of what drives chemical change. The decomposition is agnostic to the definition of atoms or fragments, and – unlike conventional EDA methods – its energy terms can in principle be estimated from experimental data. Electronegativity, defined as the average energy of valence electrons, is the interpretative backbone of EQC,3, 4 and we argue that it renders trends in some EQC-EDA terms qualitatively predictable from tabulated electronegativities and simple molecular-orbital arguments. After introducing the methodology, we show how an expression for the average electron energy within Density Functional Theory (DFT)5 provides a physically motivated constraint for rescaling Kohn–Sham energy levels. The resulting EQC-EDA, implemented in PySCF, is basis-set-insensitive and applicable across the periodic table. The approach cleanly distinguishes familiar bonding patterns such as ionic, covalent, and hydrogen bonding