Chemical bonding in the pentaerythritol tetranitrate crystal based on the experimental electron density obtained from X-ray diffraction data at 100 K and theoretical calculations at the experimental molecular geometry have been analyzed in terms of the Quantum Theory of Atoms in Molecules. Features of the intra- and intermolecular bond critical points and the oxygen atom lone-pair locations are discussed. Numerous intermolecular bonding interactions, including O...H and O...O, have been found and characterized. Atomic charges and atomic energies were integrated and compared with those for similar compounds. The N-O topological bond orders have been calculated for the first time, and the PETN atomic valences have been estimated.

This study provides a detailed description of noncovalent interactions of different types and strengths in the title crystal using a combined experimental and theoretical study of the charge density distribution. The nature of the noncovalent interactions is visualized using information theory and through the superposition of the gradient fields in the electron density and electrostatic potential. The energy of the intramolecular O–H···O bond, intermolecular C–H···O bonds, and π-stacking interactions, E int, are evaluated from empirical correlations between E int and geometrical and electron-density bond critical point parameters. The complete set of noncovalent interactions including the strong intramolecular O–H···O (E int > 90 kJ/mol) and weak C–H···O (E int < 10 kJ/mol) hydrogen bonds, and π-stacking interactions (E int < 4 kJ/mol) is quantitatively described. The results from the experimental charge density analysis are compared with periodic quantum calculations using density functional theory with the Grimme dispersion correction. It was found that the Grimme dispersion correction did not provide a good simultaneous description of both weak and strong noncovalent interactions in the studied crystal. It is shown that the obtained energies of noncovalent interactions lead to a reasonable value of the lattice energy. The latter is treated as the total intermolecular interaction energy.