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

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 '.