We investigated geometry, energy,
${\nu_{{\text{N--H}}}}$ harmonic frequencies,
14N nuclear quadrupole coupling tensors, and
${n_{\rm O}\to \sigma _{{\text{N--H}}}^\ast}$ charge transfer properties of (acetamide)
n clusters, with
n = 1 ? 7, by means of second-order Møller-Plesset perturbation theory (MP2) and DFT method. Dependency of dimer stabilization energies and equilibrium geometries on various levels of theory was examined. B3LYP/6-311++G** calculations revealed that for acetamide clusters, the average hydrogen-bonding energy per monomer increases from ?26.85
kJ mol
?1 in dimer to ?35.12 kJ mol
?1 in heptamer; i.e., 31% cooperativity enhancement. The
n-dependent trend of
${\nu_{{\text{N--H}}}\,{and}\,^{14}}$ N nuclear quadrupole coupling values were reasonably correlated with cooperative effects in
${r_{{\text{N--H}}}}$ bond distance. It was also found that intermolecular
${n_{\rm O}\to \sigma_{{\text{N--H}}}^\ast}$ charge transfer plays a key role in cooperative changes of geometry, binding energy,
${\nu_{{\text{N--H}}}}$ harmonic frequencies, and
14N electric field gradient tensors of acetamide clusters. There is a good linear correlation between
14N quadrupole coupling constants,
C Q (
14N), and the strength of Fock matrix elements (
F ij ). Regarding the
${n_{\rm O}\to \sigma_{{\text{N--H}}}^\ast}$ interaction, the capability of the acetamide clusters for electron localization, at the N–H· · ·O bond critical point, depends on the cluster size and thereby leads to cooperative changes in the N–H· · ·O length and strength, N–H stretching frequencies, and
14N quadrupole coupling tensors.
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