Rearrangement of the Fulminate Anion (CNO-) to the Cyanate Anion (OCN-). Possible Intermediacy of the Oxazirinyl Anion

1986 ◽  
Vol 39 (6) ◽  
pp. 913 ◽  
Author(s):  
WK Li ◽  
J Baker ◽  
L Radom
Keyword(s):  
Gas Phase ◽  
Electron Correlation ◽  
Basis Set ◽  
Intramolecular Rearrangement ◽  
Molecular Orbital Calculations ◽  
Potential Well ◽  
Electron Loss ◽  
Diffuse Function ◽  
Moller Plesset ◽  
High Level

The rearrangement of the fulminate anion (CNO-) to the cyanate anion (OCN-) has been examined by using high-level ab initio molecular orbital calculations which include a diffuse-function-augmented polarization basis set and electron correlation incorporated at the full fourth-order Moller-Plesset level (MP4). The reaction is predicted to be exothermic by 275 kJ mol-1. Our best calculations indicate theinvolvement of a metastable cyclic oxazirinyl anion intermediate. However, this lies in an extremely shallow potential well and, in contrast to the predictions of semiempirical calculations, is unlikely to have more than a fleeting existence. The fulminate and cyanate anions are calculated to be stable with respect to electron loss and stable with respect to intramolecular rearrangement; accordingly, both should be observable gas-phase species.

scholarly journals An ab initio study on the insertion reactions of CH [X2II] with NH3, H2O, and HF

1996 ◽  
Vol 74 (6) ◽  
pp. 910-917 ◽  
Author(s):  
Zhi-Xiang Wang ◽  
Ruo-Zhuang Liu ◽  
Ming-Bao Huang ◽  
Zhonghua Yu
Keyword(s):  
Ab Initio ◽  
Electron Correlation ◽  
Lower Energy ◽  
Energy Surface ◽  
Molecular Orbital Calculations ◽  
Ab Initio Study ◽  
Insertion Reactions ◽  
Moller Plesset ◽  
Ch Radical ◽  
Water Hydrogen

The mechanisms of the reactions of CH (X2II) with NH3, H2O, and HF have been studied by means of ab initio molecular orbital calculations incorporating electron correlation with Møller–Plesset perturbation theory up to the second order. For each of the three CH reactions, the insertion path has been found in the potential energy surface; in the calculated insertion path there exists an intermediate complex prior to the transition state that has a lower energy than the reactants. Energetic results indicate that insertion paths are favourable channels for these CH reactions, which is in line with proposals based on kinetic experiments. Key words: CH radical, ammonia, water, hydrogen fluoride, reaction mechanism.

scholarly journals An Assessment of Computational Methods for Calculating Accurate Structures and Energies of Bio-Relevant Polysulfur/Selenium-Containing Compounds

Molecules ◽  
2018 ◽  
Vol 23 (12) ◽  
pp. 3323 ◽  
Author(s):  
Sahar Nikoo ◽  
Paul Meister ◽  
John Hayward ◽  
James Gauld
Keyword(s):  
Inorganic Chemistry ◽  
Bond Length ◽  
Gas Phase ◽  
Electron Correlation ◽  
Negative Charge ◽  
Basis Set ◽  
Proton Affinities ◽  
Selenium Compounds ◽  
Gas Phase Basicities

The heavier chalcogens sulfur and selenium are important in organic and inorganic chemistry, and the role of such chalcogens in biological systems has recently gained more attention. Sulfur and, to a lesser extent selenium, are involved in diverse reactions from redox signaling to antioxidant activity and are considered essential nutrients. We investigated the ability of the DFT functionals (B3LYP, B3PW91, ωB97XD, M06-2X, and M08-HX) relative to electron correlation methods MP2 and QCISD to produce reliable and accurate structures as well as thermochemical data for sulfur/selenium-containing systems. Bond lengths, proton affinities (PA), gas phase basicities (GPB), chalcogen–chalcogen bond dissociation enthalpies (BDE), and the hydrogen affinities (HA) of thiyl/selenyl radicals were evaluated for a range of small polysulfur/selenium compounds and cysteine per/polysulfide. The S–S bond length was found to be the most sensitive to basis set choice, while the geometry of selenium-containing compounds was less sensitive to basis set. In mixed chalcogens species of sulfur and selenium, the location of the sulfur atom affects the S–Se bond length as it can hold more negative charge. PA, GPB, BDE, and HA of selenium systems were all lower, indicating more acidity and more stability of radicals. Extending the sulfur chain in cysteine results in a decrease of BDE and HA, but these plateau at a certain point (199 kJ mol−1 and 295 kJ mol−1), and PA and GPB are also decreased relative to the thiol, indicating that the polysulfur species exist as thiolates in a biological system. In general, it was found that ωB97XD/6-311G(2d,p) gave the most reasonable structures and thermochemistry relative to benchmark calculations. However, nuances in performance are observed and discussed.

Theoretical study on the insertion reaction of CH(X2Π) with CH4

1997 ◽  
Vol 75 (7) ◽  
pp. 996-1001 ◽  
Author(s):  
Zhi-Xiang Wang ◽  
Ming-Bao Huang. ◽  
Ruo-Zhuang Liu
Keyword(s):  
Electron Correlation ◽  
Energy Surface ◽  
Theoretical Study ◽  
Reaction Path ◽  
Basis Sets ◽  
Insertion Reaction ◽  
Molecular Orbital Calculations ◽  
Insertion Reactions ◽  
Moller Plesset ◽  
Ch Radical

The CH + CH4 reaction has been studied by means of ab initio molecular orbital calculations incorporating electron correlation with Møller–Plesset perturbation theory up to second and fourth orders with the 6-31G(d,p) and 6-311++G(2d,p) basis sets. An energetically feasible insertion reaction path has been found in the potential energy surface that confirms the experimental proposal for the mechanism of the CH + CH4 reaction. The feature of the mechanism for the CH + CH4 insertion reaction is found to be different from the feature of the mechanisms for the CH + NH3, CH + H2O, and CH + HF insertion reactions, but somewhat similar to that for the CH2 + CH4 insertion reaction. Energetic results for the CH + CH4 reactions are in agreement with experiment. Keywords: CH radical, methane, reaction mechanism.

One-proton and multiproton hydrogen bonds between ammonium ions and hydrogen fluoride

1985 ◽  
Vol 63 (7) ◽  
pp. 1562-1567 ◽  
Author(s):  
Henryk T. Flakus ◽  
Russell J. Boyd
Keyword(s):  
Hydrogen Fluoride ◽  
Electron Correlation ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Correlation Effects ◽  
Ammonium Ions ◽  
Electron Correlation Effects ◽  
The One ◽  
Bonded Complexes ◽  
Hydrogen Bonded

Extensive abinitio molecular orbital calculations are reported for the hydrogen bonded complexes of the formula [Formula: see text] and, [Formula: see text] where m = 0, 1, 2, and 3. The one-proton ("linear") hydrogen bonded complexes of the ammonium ions and hydrogen fluoride are predicted to be more stable by about 1 or 2 kcal/mol than the two- and three-proton ("bent") complexes. Several systematic trends and a number of differences between the neutral and protonated series of complexes are observed. The basis set dependence of the results, basis set superposition errors and electron correlation effects are discussed.

scholarly journals A Statistically Supported Antioxidant Activity DFT Benchmark—The Effects of Hartree–Fock Exchange and Basis Set Selection on Accuracy and Resources Uptake

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 5058
Author(s):  
Maciej Spiegel ◽  
Andrzej Gamian ◽  
Zbigniew Sroka
Keyword(s):  
Density Functional ◽  
Optimal Level ◽  
Basis Set ◽  
Basis Sets ◽  
Linear Regression Models ◽  
Functional Theory ◽  
Hartree Fock ◽  
Diffuse Function ◽  
Vertical Electron Affinity ◽  
High Level

Polyphenolic compounds are now widely studied using computational chemistry approaches, the most popular of which is Density Functional Theory. To ease this process, it is critical to identify the optimal level of theory in terms of both accuracy and resource usage—a challenge we tackle in this study. Eleven DFT functionals with varied Hartree–Fock exchange values, both global and range-separated hybrids, were combined with 14 differently augmented basis sets to calculate the reactivity indices of caffeic acid, a phenolic acid representative, and compare them to experimental data or a high-level of theory outcome. Aside from the main course, a validation of the widely used Janak’s theorem in the establishment of vertical ionization potential and vertical electron affinity was evaluated. To investigate what influences the values of the properties under consideration, linear regression models were developed and thoroughly discussed. The results were utilized to compute the scores, which let us determine the best and worst combinations and make broad suggestions on the final option. The study demonstrates that M06–2X/6–311G(d,p) is the best fit for such research, and, curiously, it is not necessarily essential to include a diffuse function to produce satisfactory results.

ELECTRON-CORRELATION EFFECTS ON GEOMETRICAL AND ELECTRONIC STRUCTURES OF SinNa CLUSTERS

1996 ◽  
Vol 03 (01) ◽  
pp. 365-369 ◽  
Author(s):  
R. KISHI ◽  
A. NAKAJIMA ◽  
S. IWATA ◽  
K. KAYA
Keyword(s):  
Electron Correlation ◽  
Basis Set ◽  
Negative Ion ◽  
Correlation Effects ◽  
Bridge Site ◽  
Site Type ◽  
Binary Clusters ◽  
The Face ◽  
Electron Correlation Effects ◽  
Moller Plesset

The geometries and energies of silicon-sodium binary clusters ( Si n Na , n=2–7) were investigated with the inclusion of electron-correlation effects using the second-order Møller–Plesset perturbation theory (MP2) with the 6-31G basis set. In addition, the fourth-order (MP4) energies were evaluated to determine the ground-state isomers. Si 4 Na cluster was calculated with the polarized 6-31G* basis set. For all of the Si n Na clusters, the most stable isomers have bridge-site type structures. Apart from the bridge-site type Si 6 Na , the structure of the most stable isomer of SinNa keeps the frame of the corresponding Si n cluster unchanged, and the electronic structure of Si n Na is similar to that of the corresponding negative ion [Formula: see text]. The silicon framework of the bridge-site type of Si 6 Na is distorted from the compressed octahedron to the face-capped trigonal bipyramid.

Low-lying states of MX2 (M = Ag, Au; X = Cl, Br and I) with coupled-cluster approaches: effect of the basis set, high level correlation and spin–orbit coupling

2020 ◽  
Vol 22 (45) ◽  
pp. 26178-26188
Author(s):  
Xingxing Pang ◽  
Minggang Guo ◽  
Zhifan Wang ◽  
Fan Wang
Keyword(s):  
Electron Correlation ◽  
Orbit Coupling ◽  
Basis Set ◽  
Coupled Cluster ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Jahn Teller ◽  
High Level ◽  
Correlation Level

Spin–orbit coupling, electron correlation level and basis set are important in describing Renner–Teller and pseudo-Jahn–Teller effects and properties of MX2.

scholarly journals Thermochemistry of Guanine Tautomers Re-Examined by Means of High-Level CCSD(T) Composite Ab Initio Methods

2019 ◽  
Vol 72 (8) ◽  
pp. 607 ◽  
Author(s):  
Amir Karton
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Basis Set ◽  
Energy Window ◽  
Small Energy ◽  
Composite Methods ◽  
Wide Range ◽  
Complete Basis Set ◽  
Enol Tautomer ◽  
High Level

We obtained accurate gas-phase tautomerization energies for a set of 14 guanine tautomers by means of high-level thermochemical procedures approximating the CCSD(T) energy at the complete basis set (CBS) limit. For the five low-lying tautomers, we use the computationally demanding W1-F12 composite method for obtaining the tautomerization energies. The relative W1-F12 tautomerization enthalpies at 298K are: 0.00 (1), 2.37 (2), 2.63 (3), 4.03 (3′), and 14.31 (4) kJmol−1. Thus, as many as four tautomers are found within a small energy window of less than 1.0kcalmol−1 (1kcalmol−1=4.184kJmol−1). We use these highly accurate W1-F12 tautomerization energies to evaluate the performance of a wide range of lower-level composite ab initio procedures. The Gn composite procedures (G4, G4(MP2), G4(MP2)-6X, G3, G3B3, G3(MP2), and G3(MP2)B3) predict that the enol tautomer (3) is more stable than the keto tautomer (2) by amounts ranging from 0.36 (G4) to 1.28 (G3(MP2)) kJmol−1. We also find that an approximated CCSD(T)/CBS energy calculated as HF/jul-cc-pV{D,T}Z+CCSD/jul-cc-pVTZ+(T)/jul-cc-pVDZ results in a root-mean-square deviation (RMSD) of merely 0.11kJmol−1 relative to the W1-F12 reference values. We use this approximated CCSD(T)/CBS method to obtain the tautomerization energies of 14 guanine tautomers. The relative tautomerization enthalpies at 298K are: 0.00 (1), 2.20 (2), 2.51 (3), 4.06 (3′), 14.30 (4), 25.65 (5), 43.78 (4′), 53.50 (6′), 61.58 (6), 77.37 (7), 82.52 (8′), 86.02 (9), 100.70 (10), and 121.01 (8) kJmol−1. Using these tautomerization enthalpies, we evaluate the performance of standard and composite methods for the entire set of 14 guanine tautomers. The best-performing procedures emerge as (RMSDs are given in parentheses): G4(MP2)-6X (0.51), CCSD(T)+ΔMP2/CBS (0.52), and G4(MP2) (0.64kJmol−1). The worst performers are CCSD(T)/AVDZ (1.05), CBS-QB3 (1.24), and CBS-APNO (1.38kJmol−1).

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