We employ natural bond orbital and natural resonance theory tools to analyze the enigmatic properties of the C2v-symmetric isomer of chlorine dioxide radical (ClO2), whose many challenges to Pauling-type localized bonding concepts were recognized by Linus Pauling himself. Although spin-contamination is minimal in this species, ClO2exhibits an unusually strong form of “different Lewis structures for different spins” bonding pattern, intrinsically outside the framework of “maximal pairing” concepts. We show how the novel spin-unpaired donor–acceptor interactions lead to weakened bonding in the supramolecular domain of polyradical (ClO2)nhomoclusters and aqueous ClO2(H2O)nheteroclusters. Despite feeble binding energies and large inter-radical separations, the polyradical clusters are found to maintain coherent spin patterns in each cluster component, attesting to the quantal donor–acceptor nature of their interactions and the cooperative and anticooperative couplings that govern intra- and intermolecular spin distributions in such spin-clusters.
Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to non-federal websites. Their policies may differ from this site.
Efficient optimization of natural resonance theory weightings and bond orders by gram‐based convex programming
We describe the formal algorithm and numerical applications of a novel convex quadratic programming (QP) strategy for performing the variational minimization that underlies natural resonance theory (NRT). The QP algorithm vastly improves the numerical efficiency, thoroughness, and accuracy of variational NRT description, which now allows uniform treatment of
allreference structures at the high level of detail previously reserved only for leading “reference” structures, with little or no user guidance. We illustrate overall QPNRT search strategy, program I/O, and numerical results for a specific application to adenine, and we summarize more extended results for a data set of 338 species from throughout the organic, bioorganic, and inorganic domain. The improved QP‐based implementation of NRT is a principal feature of the newly released NBO 7.0program version. © 2019 Wiley Periodicals, Inc.
To Be or Not to Be: Demystifying the 2nd‐Quantized Picture of Complex Electronic Configuration Patterns in Chemistry with Natural Poly‐Electron Population Analysis
We provide a didactic introduction to 2nd‐quantized representation of complex electron–hole (
e/ h) excitation patterns in general configuration interaction wave functions built from orthonormal local orbitals of natural atomic orbital or natural bond orbital (NBO) type. Such local excitation patterns of chemically oriented basis functions can be related to the resonance concepts of valence bond theory, and quantitative evaluation of the associated excitation probabilities then provides an alternative assessment of resonance “weighting” that may be compared with those of NBO‐based natural resonance theory. We illustrate the usefulness of anticommutation relations in deriving Pauli‐compliant expressions for allowed excitation patterns, showing how the exciton‐like promotions φλ → φν(creating an e/ hexcitation with hin φλand ein φν) impose strict constraints on associated e/ h‐probabilities (requiring, e.g., that the e‐probability for an electron “to be” or “not to be” in φνmust be rigorously linked to the complementary h‐probabilities in φλ). Specific examples are presented of the quantum Boolean logic for four or six local spin‐orbitals, with emphasis on Natural Poly‐Electron Population Analysis (NPEPA) evaluation of VB‐type covalent and ionic contributions in conventional 2‐center bonding, resonance weightings in 3‐center hydrogen bonding, and general characteristics of higher‐order m‐center bonding motifs for m> 3. Numerical results are presented for methylamine, acrolein, and water dimer to illustrate current NPEPA implementation in themore »