A QTAIM and Stress Tensor Perspective of Large-Amplitude Motions of the Tetrasulfur Tetranitride S4N4 Molecular Graph

The nature of the bonding interactions including the intramolecular S-S interactions in tetrasulfur tetranitride, S4N4 are probed by performing very large amplitude vibrations of all of the 18 normal modes of vibration. The QTAIM and stress tensor point properties are - then investigated and found to be highly dependent on the mode of vibration. A considerable degree of metallicity xi(r(b)) is found for the S-S and S-N bonding interactions. A unique bonding feature is found for a small amplitude vibration of the most anharmonic mode of this investigation, mode 2, where the S-S bond critical point (BCP) transforms from a closed-shell S-S BCP to a shared-shell S-S BCP. We find 17 new unique QTAIM topologies for the molecular graphs corresponding to the 18 modes of vibration along with seven "missing" topologies that are mapped onto a spanning 2-D Quantum topology Phase Diagram (QTPD). In addition, eleven unique topologies existing on 3-D QTPDs are found due to the presence of non-nuclear attractors (NNAs). We use the stress tensor eigenvalues to explain the invariance of the numbers and types of QTAIM critical points. The applicability of both the stiffness S and stress tensor stiffness S-r are also explored. Two new bond measures are introduced, a polarizability P and the stress tensor polarizability P-r which are derived from the stiffness S and stress tensor stiffness S-r, respectively. (C) 2016 Wiley Periodicals, Inc.