Polyrate 2023: A computer program for the calculation of chemical reaction rates for polyatomics. New version announcement
Not Available
Meana-Pañeda, Rubén↗
Engineering topics
Bao, Junwei Lucas
Publications and source records attributed to Bao, Junwei Lucas.
MSTor 2023 : A new version of the computer code for multistructural torsional anharmonicity, now with automatic torsional identification using redundant internal coordinates
The MSTor program is a computer program for calculating partition functions and thermodynamic functions of complex gas-phase molecules with multiple torsions; the multi-structural approximation with torsional anharmonicity (MS-T) can be used based on either a coupled torsional potential or an uncoupled torsional potential. The program can also carry out calculations in the multiple-structure local harmonic (MS-LH) approximation or multi-structural local quasiharmonic (MS-LQ) approximation or by the dual-level MS-T method. Furthermore, the program package includes eight utility codes that can be used as stand-alone programs to help the user to generate the input files for the code or to generate comparison results. The 2023 version of MSTor includes a new capability, namely automatic identification of torsional modes with redundant internal coordinates.
97 MATHEMATICS AND COMPUTING↗
Predicting Bond Dissociation Energies and Bond Lengths of Coordinatively Unsaturated Vanadium–Ligand Bonds
Understanding the electronic structure of coordinatively unsaturated transition-metal compounds and predicting their physical properties are of great importance for catalyst design. Bond dissociation energy D e and bond length r e are two of the fundamental quantities for which good predictions are important for a successful design strategy. In the present work, recent experimentally measured bond energies and bond lengths of VX diatomic molecules (X = C, N, S) are used as a gauge to consider the utility of a number of electronic structure methods. Single-reference methods are one focus because of their efficiency and utility in practical calculations, and multireference configuration interaction (MRCISD) methods and a composite coupled cluster (CCC) method are a second focus because of their potential high accuracy. The comparison is especially challenging because of the large multireference M diagnostics of these molecules, in the range 0.15–0.19. For the single-reference methods, Kohn–Sham density functional theory (KS-DFT) has been tested with a variety of approximate exchange-correlation functionals. Of these, MOHLYP provides the bond dissociation energies in best agreement with experiments, and BLYP provides the bond lengths that are in best agreement with experiments; but by requiring good performance for both the D e and r e of the vanadium compounds, MOHLYP, MN12-L, MGGA_MS1, MGGA_MS0, O3LYP, and M06-L are the most highly recommended functionals. The CCC calculations include up to connected pentuple excitations for the valence electrons and up to connected quadruple excitations for the core–valence terms; this results in highly accurate dissociation energies and good bond lengths. In conclusion, averaged over the three molecules, the mean unsigned deviation of CCC bond energies from experimental ones is only 0.4 kcal/mol, demonstrating excellent convergence of theory and experiments.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Salt-rich solid electrolyte interphase for safer high-energy-density Li metal batteries with limited Li excess
We propose a carbonate-based electrolyte optimized with dual cations and ionic liquid for high-efficiency Li metal batteries with a high-voltage cathode. An average coulombic efficiency of Li deposition of 99.6% is achieved due to the salt-rich solid electrolyte interphase and Na guided uniform Li plating. The Li||NCM811 cells can be cycled with limited Li (N/P = 1) over 90 cycles. An additional advantage is that it improves the thermal stability of the NCM811 cathode.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A versatile single-ion electrolyte with a Grotthuss-like Li conduction mechanism for dendrite-free Li metal batteries
A new versatile single-ion electrolyte with a Grotthuss-like Li conduction mechanism is proposed to address the issue of Li metal batteries.
Yuan, Shouyi↗
Dual Lithiophilic Structure for Uniform Li Deposition
The development of Li metal anode is hindered by the Li dendrites arising from the random deposition of Li metal during cycles. Hence, uniform deposition of Li during repeated cycles is crucial for the development of Li metal batteries. However, it is difficult to regulate Li deposition due to convection in the electrolyte. Here, we employ a dual lithiophilic structure composed of polar metal organic framework (MOF) and highly conductive Ag nanoparticles, and we show that it brings about uniform lithium deposition. Here, the binding energy for Li is increased by the abundant oxygen sites and large surface area of the MOF, and concomitantly the uniform distribution of Li nuclei can be achieved with a low nucleation overpotential. When highly conductive lithiophilic Ag is incorporated into the MOF, the binding energy for Li is further increased and the nucleation overpotential is decreased to nearly zero. As a result, Li platting and stripping on the Ag@MOF (i.e., Ag@HKUST-1) substrate exhibits a Coulombic efficiency (CE) of 97% over 300 cycles and a high areal capacity of 5 mAh cm -2 without dendrite formation.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Effect of energy dependence of the density of states on pressure-dependent rate constants
The F E integral for the normalized Boltzmann-weighted number of unimolecular states above the threshold energy is the key quantity for computing the collision efficiency in the pressure-dependent unimolecular rate theory developed by Troe, who calls this the energy dependence factor of the density of states. By using the Whitten–Rabinovitch approximation and assuming that the Whitten–Rabinovitch a(E) function is independent of energy, F E can be approximated by an analytical formula; this approximate formula is widely used because of its convenience and computational efficiency. Here we test its validity by comparing the rate constants computed by using the approximate F E to the ones determined by using the numerically integrated F E . For small-sized molecules and for reactions with high threshold energies E 0 , the differences are negligible at all temperatures, but in other cases, the approximate formula tends to underestimate F E and thus overestimates the collision efficiency, and this leads to smaller pressure falloff. When a(E) at high energies differs appreciably from a(E 0 ), we find that the underestimation of pressure-dependent rate constants by using the approximate formula can be greater than a factor of 5 at high temperatures. The physical insight we draw from this study is that, for reactions with threshold energies below about 30 kcal mol -1 , the rate of collisional energy transfer can be appreciably slowed down by the increase in the density of states at higher energies, and this increases the falloff effect by which finite-pressure rate constants become lower than the high-pressure limit, especially at higher temperatures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Kinetics of the Strongly Correlated CH 3 O + O 2 Reaction: The Importance of Quadruple Excitations in Atmospheric and Combustion Chemistry
Kinetics measurements on radical–radical reactions are often unavailable experimentally, and obtaining quantitative rate constants for such reactions by theoretical methods is challenging because the transition states and the reactants are often strongly correlated. Treating strongly correlated systems by coupled cluster theory limited to single, double, and triple connected excitations is often inadequate. We therefore use a new method, called GMM(P), for extrapolation to the complete configuration interaction limit to go beyond triple excitations and in particular to approximate the CCSDTQ(P)/CBS limit. Here, we present this method and use it to investigate the CH 3 O + O 2 reaction. The contribution of connected quadruple excitations to the barrier height energy is found to be -3.13 kcal/mol, and adding a quasiperturbative calculation of the effect of connected pentuple excitations brings the post-connected-triples contributions to -3.44 kcal/mol, which corresponds to Boltzmann factors that increase calculated rate constants by factors of 1.0 × 10 3 , 3.3 × 10 2 , and 18 at 250, 298, and 600 K, respectively. We present rate constants for temperatures from 250 to 2000 K, and we find that the Arrhenius activation energy increases from 0.58 to 9.68 kcal/mol over this range. We also find reasonably good accuracy for the barrier height with the MN15-L exchange–correlation functional, and we calculate rate constants by a combination of GMM(P) and MN15-L electronic structure calculations and conventional and variational transition state theory, in particular canonical variational theory with small-curvature tunneling. The present findings have broad implications for obtaining quantitative rate constants for complex reaction systems in atmospheric and combustion chemistry.
Chemistry↗
Hydrogen shift isomerizations in the kinetics of the second oxidation mechanism of alkane combustion. Reactions of the hydroperoxypentylperoxy OOQOOH radical
Hydroperoxyalkylperoxy species are important intermediates that are generated during the autoignition of transport fuels. In combustion, the fate of hydroperoxyalkylperoxy is important for the performance of advanced combustion engines, especially for autoignition. A key fate of the hydroperoxyalkylperoxy is a 1,5 H-shift, for which kinetics data are experimentally unavailable. In the present work, we study 1-hydroperoxypentan-3-yl)dioxidanyl (CH 3 CH 2 CH(OO)CH 2 CH 2 OOH) as a model compound to clarify the kinetics of 1,5 H-shift of hydroperoxyalkylperoxy species, in particular α-H isomerization and alternative competitive pathways. With a combination of electronic structure calculations, we determine previously missing thermochemical data, and with multipath variational transition state theory (MP-VTST), a multidimensional tunneling (MT) approximation, multiple-structure anharmonicity, and torsional potential anharmonicity, we obtained much more accurate rate constants than the ones that can computed by conventional single-structure harmonic transition state theory (TST) and than the empirically estimated rate constants that are currently used in combustion modeling. The roles of various factors in determining the rates are elucidated. The pressure-dependent rate constants for these competitive reactions are computed using system-specific quantum RRK theory. The calculated temperature range is 298–1500 K, and the pressure range is 0.01–100 atm. The accurate thermodynamic and kinetics data determined in this work are indispensable in the detailed understanding and prediction of ignition properties of hydrocarbons and alternative fuels.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Unimolecular reaction of acetone oxide and its reaction with water in the atmosphere
Significance Obtaining rate constants and tropospheric lifetimes of Criegee intermediates is of critical significance for atmospheric modeling. We report calculations that can produce quantitative rate constants by variational transition state theory with corner-cutting tunneling based on implicit potential energy surfaces calibrated against high-level calculations. Demonstration of this capability is particularly significant because the calculations can fully cover the atmospheric conditions, which is hard to do by experiment. The present results also show the usefulness of the M11-L and MN15-L density functionals in describing this nominally multireference system. Modern quantum chemistry is now accurate enough to be used for atmospheric chemistry, and the present methods and strategies can be also be used to study other atmospherically important reactions of other medium-sized molecules.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Über Oxidationszahl‐Obergrenzen in der Chemie
Abstract Der Begriff Oxidationszahl ( OS ) ist auf der Basis des Lewis‐Elektronenpaar‐Bildes definiert, wobei Bindungselektronen dem jeweils elektronegativeren Element zugeordnet werden. Der Begriff ist hilfreich zur “Buchhaltung” der Elektronen, zur Vorhersage von chemischen Trends und zur Planung von Synthesewegen. Experimentelle und quantenchemische Befunde legen eine obere Grenze von etwa +8 für die OS in stabilen (neutralen) chemischen Substanzen unter normalen Bedingungen nahe. OS =+9 wurde für das isolierte [IrO 4 ] + ‐Kation in der Gasphase beobachtet. Vorhergesagte OS =+10 für das isolierte [PtO 4 ] 2+ ‐Kation wird hier theoretisch nur für tiefe Temperaturen bestätigt, konnte aber noch nicht experimentell verifiziert werden. Verbindungen mit hoher OS tendieren zur spontanen Reduktion des zentralen Metallatoms unter Oxidation der Liganden, etwa von O −2 unter Bildung von . O −1 und O‐O‐Bindungen, wobei nicht‐Lewis‐konforme Strukturen gebildet werden können.
Hu, Shu‐Xian↗
On the Upper Limits of Oxidation States in Chemistry
The concept of oxidation state (OS) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum-chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS=+9 was observed for the isolated [IrO4] + cation in vacuum. The prediction of OS=+10 for isolated [PtO4]2+cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. Lastly, for high OS species, oxidation of the ligands, for example, of O -2 with formation of.O –1 and O–O bonds, and partial reduction of the metal center may be favorable, possibly leading to non-Lewis type structures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Predicting Bond Dissociation Energies of Transition-Metal Compounds by Multiconfiguration Pair-Density Functional Theory and Second-Order Perturbation Theory Based on Correlated Participating Orbitals and Separated Pairs
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catalysis (heterogeneous), materials and chemistry↗