This work reports hydrogen bonding interaction in linear formaldehyde oligomers using density functional theory method. Many-body analysis technique has been used to study the various interactions in these oligomers and to obtain % contributions from individual many-body energy terms to the binding energies of these oligomers. Co-operativity effects are studied using different indicators viz. hydrogen bond strength, inter- and intramolecular distances, dissociation energy, dipole co-operativity, energy per hydrogen bond, excess energy and non-additive energy. All these indicators show strong positive hydrogen bond co-operativity in linear formaldehyde oligomers. The dipole moment changes from 2.51 D in monomer to 20.92 D in formaldehyde heptamer.
This work reports hydrogen bonding interaction in cyclic and ladder oligomers using density functional theory method. Many-body analysis technique has been used to study the nature of interactions between different molecules and their contribution to the binding energy of a respective hydrogen bonded oligomers. Hydrogen bonds in cyclic trimer to pentamer are stronger than those in corresponding ladder structures. Cyanamide monomer shows the lowest energy at B3LYP/aug-cc-pvdz level among different methods used here with the same basis set. The geometrical parameters for cyanamide monomer obtained at B3LYP/aug-cc-pvdz level are in excellent agreement with the experimental determinations. Cyclic structures are more stable than the ladder. In cyclic oligomers not only total two-body energies, but higher body energies also contribute significantly to the binding energy of a respective complex whereas in ladder, only total two-body energies contribute significantly and higher-body energies are almost negligible for cyanamide trimer to pentamer.
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