31P NMR spectroscopy Bader charge analysis CPMD DFT IINS IR IR spectroscopy Lewis acid-Lewis base interactions NMR QTAIM Raman Reaction mechanism Research & information: general activation energy adenine aromaticity azo dyes benchmark carboxyl group computation of low-frequency Raman spectra condensed matter confinement conventional and non-conventional H-bonds crystal engineering density functional theory deuteration dispersion electron charge shifts empirical Grimme corrections external electric field