Extended Energy Divide-and-Conquer Method Based on Charge Conservation

The divide-and-conquer (DC) scheme, the most popular linear-scaling method, is very important in the quantum mechanics computation of large systems. However, when a chemical system is divided into subsystems, its covalent bonds are often broken and then capped by complementary atoms/groups. In this paper, we show that the charge transfer between subsystems and the complementary atoms/groups causes the nonconservation of the total charge of the whole system, and this is the main source of error for the computed total energy. On the basis of this finding, an extension of the many-body expansion method (energy-based divide-and-conquer, EDC) utilizing charge conservation (E-EDC) is proposed. In the E-EDC method, initially the total energies of the whole system at different many-body correction levels are computed according to the EDC scheme. The total charges of the whole system, that is, the sum of the charges of the subsystems without cap atoms/groups at different many-body correction levels, are also computed. Then the total energy is extrapolated to the value at which the net charge of the whole system equals to the real value. Other properties such as atomic forces can also be extrapolated in a similar way. In the test of 24 and 32 glycine oligomers, this scheme reduces the error of the total energy by about 40–70%, but the computational cost is almost the same as that of the EDC scheme

Formation and Infrared Spectroscopic Characterization of Three Oxygen-Rich BiO₄ Isomers in Solid Argon

The reactions of bismuth atoms and O₂ have been investigated using matrix isolation infrared spectroscopy and density functional theory calculations. The ground state bismuth atoms react with dioxygen to form the BiOO and Bi­(O₂)₂ complexes spontaneously on annealing. The BiOO molecule is characterized to be an end-on bonded superoxide complex, while the Bi­(O₂)₂ molecule is characterized to be a superoxo bismuth peroxide complex, [Bi³⁺(O₂^–)­(O₂^2‑)]. Under UV–visible light irradiation, the Bi­(O₂)₂ complex rearranges to the more stable OBiOOO isomer, an end-on bonded bismuth monoxide-ozonide complex. The end-on-bonded OBiOOO complex further rearranges to a more stable side-on bonded OBiO₃ isomer upon sample annealing. In addition, the bent bismuth dioxide anion is also formed and assigned

Organoborane Catalyzed Regioselective 1,4-Hydroboration of Pyridines

A bulky organoborane Ar^F₂BMe (Ar^F = 2,4,6-tris­(trifluoromethyl)­phenyl, <b>1</b>) has been synthesized. In C₆D₆ solution this organoborane and pyridine form a frustrated Lewis pair. Under mild conditions, <b>1</b> can efficiently catalyze 1,4-hydroboration of a series of pyridines. This reaction is highly chemo- and regioselective. The reaction intermediate, a boronium complex [Py₂Bpin]­[Ar^F₂B­(H)­Me] (<b>3</b>), was characterized in solution by NMR spectroscopy, which was also confirmed by DFT calculation

Generalized Switch Functions in the Multilevel Many-Body Expansion Method and Its Application to Water Clusters

The many-body expansion (MBE) method is the basis of many fragment-based methods and is widely applied to the computation of large molecular systems. To reach linear-scaling computation, a cutoff must be used to discard those subsystems with long interfragment distances. However, this leads to a discontinuous potential energy surface (PES) that would cause various problems in geometry optimizations and molecular dynamics simulations. To solve this problem, we present a generalized-switch-function (GSF) approach to smooth the PES computed by the MBE method with the use of a cutoff distance. The GSFs are naturally normalized and are permutation invariant. This approach can be applied to adaptively computing any order of many-body correction energies with multilevel computational methods and is a dynamic subsystem approach. We have applied the two versions of our method, GSF-MBE­(<i>m</i>)/L₁ and GSF-MBE­(<i>m</i>)/(L₁:L₂:L₃), to water clusters. Thorough tests show that our method can indeed give smooth potential-energy surface and is linear scaling but without losing much accuracy for very large water clusters with appropriately chosen cutoff distances

Infrared Photodissociation Spectroscopic and Theoretical Study of Homoleptic Dinuclear Chromium Carbonyl Cluster Cations with a Linear Bridging Carbonyl Group

Infrared spectra of mass-selected homoleptic dinuclear chromium carbonyl cluster cations Cr₂(CO)_<i>n</i>⁺ with <i>n</i> = 7–9 are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region in the gas phase. The structures are established by comparison of the experimental spectra with the simulated spectra derived from density functional calculations. The Cr₂(CO)_<i>n</i>⁺ cluster cations are characterized to have the (OC)₅Cr–C–O–Cr­(CO)_<i>n</i>−6⁺ structures with a linear bridging carbonyl group bonded to one chromium atom through its carbon atom and to the other chromium atom through its oxygen atom. The cluster cations all have a sextet ground state with the positive charge and the unpaired electrons located on the Cr­(CO)_<i>n</i>−6 moiety. The formation of the linear bridging structures without Cr–Cr bonding can be rationalized that chromium forms strong Cr–CO bonds but weak Cr–Cr bonds

Synthesis and Reactivity of the CO₂ Adducts of Amine/Bis(2,4,6-tris(trifluoromethyl)phenyl)borane Pairs

Frustrated Lewis pairs (FLPs) comprised of bis­(2,4,6-tris­(trifluoromethyl)­phenyl)­borane (<b>1</b>) and a secondary amine (such as HN<i>i</i>Pr₂ or HNEt₂) readily react with CO₂ at room temperature to afford ammonium carbamatoborate salts <b>2</b>. When the reaction was carried out at 80 °C, carbamate boryl esters <b>3</b> were obtained with release of 1 equiv of H₂. The <i>i</i>Pr-substituted carbamate boryl ester <b>3a</b> can function as an intramolecular FLP to activate H₂, affording ammonium borylformate salt <b>4a</b> and formamide adduct <b>5a</b>. Two reaction pathways leading to the formation of <b>4a</b> and <b>5a</b> are proposed

Infrared Photodissociation Spectroscopy of the Ni(O₂)_<i>n</i>⁺ (<i>n</i> = 2–4) Cation Complexes

The infrared spectra of mass-selected Ni­(O₂)_<i>n</i>⁺ (<i>n</i> = 2–4) and their argon-tagged complexes are measured by infrared photodissociation spectroscopy in the gas phase. The experimental spectra provide distinctive patterns allowing the determination of their geometric and electronic structures by comparison with the simulated vibrational spectra from density functional theory calculations. The [Ni­(O₂)₂Ar₂]⁺ cation complex was determined to have <i>D</i>_2<i>h</i> symmetry involving a Ni­(O₂)₂⁺ core ion with two equivalent superoxide ligands side-on bound to a Ni³⁺ cation center. The higher Ni­(O₂)₃⁺ and Ni­(O₂)₄⁺ cation complexes were determined to have structures with a chemically bound Ni­(O₂)₂⁺ core ion that is weakly coordinated by neutral O₂ molecule(s)

Carbonyl Bonding on Oxophilic Metal Centers: Infrared Photodissociation Spectroscopy of Mononuclear and Dinuclear Titanium Carbonyl Cation Complexes

Mononuclear and dinuclear titanium carbonyl cation complexes including Ti­(CO)₆⁺, Ti­(CO)₇⁺, TiO­(CO)₅⁺, Ti₂(CO)₉⁺ and Ti₂O­(CO)₉⁺ are produced via a laser vaporization supersonic cluster source. The ions are mass selected in a tandem time-of-flight mass spectrometer and studied with infrared photodissociation spectroscopy in the CO stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. Only one IR band is observed for the 15-electron Ti­(CO)₆⁺ cation, which is characterized to have an octahedral <i>O</i>_<i>h</i> structure. The Ti­(CO)₇⁺ cation is determined to be a weakly bound complex involving a Ti­(CO)₆⁺ core ion instead of the seventh coordinated ion. The TiO­(CO)₅⁺ cation has a completed coordination sphere with a C_4v structure. The Ti₂(CO)₉⁺ cation is determined to have a doublet <i>C</i>_<i>s</i> structure with two four-electron donor side-on bridging CO groups and one semibridging CO group. The Ti₂O­(CO)₉⁺ cation has a doublet <i>C</i>_<i>s</i> structure involving a planar cyclic Ti₂O­(η²-μ-CO) core with a four electron donor side-on bridging CO. Bonding analysis indicates that the Ti₂(CO)₉⁺ and Ti₂O­(CO)₉⁺ cations each have a Ti–Ti single bond. The results suggest that metal–metal multiple bonding is not favorable, and the oxophilic titanium centers failed to satisfy the 18-electron configuration in these metal carbonyl complexes

Undercoordinated Site-Abundant and Tensile-Strained Nickel for Low-Temperature CO_<i>x</i> Methanation

By means of the rapid quenching (RQ) technique, we fabricate RQ Ni with peculiar undercoordinated site (UCS) abundant and tensile-strained structural characteristics. In liquid-phase CO methanation at 473 K, RQ Ni displays markedly higher specific activity and CH₄ selectivity in comparison to Raney Ni, supported Ni, and Al₂O₃-supported Pd and Pt. RQ Ni shows comparable activity but higher CH₄ selectivity in comparison to Ru/Al₂O₃, with Ru being documented as the most active metal for CO methanation. Density functional theory (DFT) calculations confirm that the UCSs are the active centers and reveal that the tensile-strain effect can further accelerate the rate-limiting CO dissociation step. Attractively, RQ Ni is also powerful in converting the greenhouse gas CO₂ to CH₄ at 473 K with an unprecedentedly high TOF of CO₂ of 86.9 × 10^–3 s^–1 and impressively high selectivity of >99%