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 NMR J-coupling constant denoted ³J(H,H’), which a number of previous studies showed to correlate well with QTAIM’s delocalisation index (DI), which is essentially a bond order. Inspired by Karplus equations, here we investigate correlations between ³J(H,H’) and a relevant dihedral angle in 6 simple initial compounds of the shape H₃C-YH_n (Y=C, N, O, Si, P and S), N-methylacetamide (as prototype of the peptide bond) and 5 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 best contact with experiment, through ³J(H,H’), when multiplied with the internuclear distance R_HH’.