Linking the Interatomic Exchange-Correlation Energy to Experimental J-Coupling Constants

[Image: see text] The main aim of the current work is to find an experimental connection to the interatomic exchange-correlation energy as defined by the energy decomposition method Interacting Quantum Atoms (IQA). A suitable candidate as (essentially) experimental quantity is the nuclear magnetic resonance (NMR) J-coupling constant denoted (3)J(H,H′), which a number of previous studies showed to correlate well with QTAIM’s delocalization index (DI), which is essentially a bond order. Inspired by Karplus equations, here, we investigate correlations between (3)J(H,H′) and a relevant dihedral angle in six simple initial compounds of the shape H(3)C-YH(n) (Y = C, N, O, Si, P, and S), N-methylacetamide (as prototype of the peptide bond), and five peptide-capped amino acids (Gly, Ala, Val, Ile, and Leu) because of the protein direction of the force field FFLUX. In conclusion, except for methanol, the inter-hydrogen exchange-correlation energy V(xc)(H,H′) makes the best contact with experiment, through (3)J(H,H′), when multiplied with the internuclear distance R(HH)′.