Post-CCSD(T) ab Initio Thermochemistry of Halogen Oxides and Related Hydrides XOX, XOOX, HOX, XOn, and HXOn(X = F, Cl), and Evaluation of DFT Methods for These Systems†

2009 ◽  
Vol 113 (16) ◽  
pp. 4802-4816 ◽  
Author(s):  
Amir Karton ◽  
Srinivasan Parthiban ◽  
Jan M. L. Martin
Keyword(s):  
Ab Initio ◽  
Dft Methods ◽  
Halogen Oxides

A Systematic DFT Study of Two Elementary Steps Involving Hydrogen Peroxide and the Hydroxyl Radical in the Fenton Reaction

2018 ◽  
Author(s):  
Danilo Carmona ◽  
David Contreras ◽  
Oscar A. Douglas-Gallardo ◽  
Stefan Vogt-Geisse ◽  
Pablo Jaque ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Hydroxyl Radical ◽  
Ab Initio ◽  
Fenton Reaction ◽  
Basis Set ◽  
Basis Sets ◽  
Dft Methods ◽  
Elementary Steps ◽  
Oxygen Oxygen ◽  
Complete Basis Set

The Fenton reaction plays a central role in many chemical and biological processes and has various applications as e.g. water remediation. The reaction consists of the iron-catalyzed homolytic cleavage of the oxygen-oxygen bond in the hydrogen peroxide molecule and the reduction of the hydroxyl radical. Here, we study these two elementary steps with high-level ab-initio calculations at the complete basis set limit and address the performance of different DFT methods following a specific classification based on the Jacob´s ladder in combination with various Pople's basis sets. Ab-initio calculations at the complete basis set limit are in agreement to experimental reference data and identified a significant contribution of the electron correlation energy to the bond dissociation energy (BDE) of the oxygen-oxygen bond in hydrogen peroxide and the electron affinity (EA) of the hydroxyl radical. The studied DFT methods were able to reproduce the ab-initio reference values, although no functional was particularly better for both reactions. The inclusion of HF exchange in the DFT functionals lead in most cases to larger deviations, which might be related to the poor description of the two reactions by the HF method. Considering the computational cost, DFT methods provide better BDE and EA values than HF and post--HF methods with an almost MP2 or CCSD level of accuracy. However, no systematic general prediction of the error based on the employed functional could be established and no systematic improvement with increasing the size in the Pople's basis set was found, although for BDE values certain systematic basis set dependence was observed. Moreover, the quality of the hydrogen peroxide, hydroxyl radical and hydroxyl anion structures obtained from these functionals was compared to experimental reference data. In general, bond lengths were well reproduced and the error in the angles were between one and two degrees with some systematic trend with the basis sets. From our results we conclude that DFT methods present a computationally less expensive alternative to describe the two elementary steps of the Fenton reaction. However, choice of approximated functionals and basis sets must be carefully done and the provided benchmark allows a systematic validation of the electronic structure method to be employed

scholarly journals Benchmark ab Initio Energy Profiles for the Gas-Phase SN2 Reactions Y-+ CH3X → CH3Y + X-(X,Y = F,Cl,Br). Validation of Hybrid DFT Methods

2001 ◽  
Vol 105 (5) ◽  
pp. 895-904 ◽  
Author(s):  
Srinivasan Parthiban ◽  
Glênisson de Oliveira ◽  
Jan M. L. Martin
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Dft Methods ◽  
Sn2 Reactions ◽  
Energy Profiles

Theoretical study of the adsorption of isobutane over H-mordenite zeolite by ab initio and DFT methods

2003 ◽  
Vol 200 (1-2) ◽  
pp. 205-212 ◽  
Author(s):  
L.A Garcı́a-Serrano ◽  
C.A Flores-Sandoval ◽  
I.P Zaragoza
Keyword(s):  
Ab Initio ◽  
Theoretical Study ◽  
Dft Methods ◽  
Ab Initio And Dft

scholarly journals How accurate are approximate quantum chemical methods at modelling solute–solvent interactions in solvated clusters?

2020 ◽  
Vol 22 (7) ◽  
pp. 3855-3866 ◽  
Author(s):  
Junbo Chen ◽  
Bun Chan ◽  
Yihan Shao ◽  
Junming Ho
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Interaction Energies ◽  
Chemical Methods ◽  
Dft Methods ◽  
Solvent Interactions ◽  
Quantum Chemical Methods ◽  
Composite Methods ◽  
Wide Range

In this paper, the performance of ab initio composite methods, and a wide range of DFT methods is assessed for the calculation of interaction energies of thermal clusters of a solute in water.

Symmetry breaking in the planar configurations of disilicon tetrahalides: Pseudo-Jahn–Teller effect parameters, hardness and electronegativity

2015 ◽  
Vol 17 (43) ◽  
pp. 29251-29261 ◽  
Author(s):  
Ghazaleh Kouchakzadeh ◽  
Davood Nori-Shargh
Keyword(s):  
Symmetry Breaking ◽  
Ab Initio ◽  
Teller Effect ◽  
Dft Methods ◽  
Jahn Teller ◽  
Jahn Teller Effect

The correlations between the Pseudo-Jahn–Teller Effect (PJTE) parameters (i.e. F, Δ and K0), structural and configurational properties, global hardness and global electronegativities in disilicon tetrahalides were investigated by means of ab initio and hybrid-DFT methods.

scholarly journals Динамические поляризуемости двухатомных молекул: сравнение методов ab initio и теории функционала плотности с методом замещенной функции Грина теории квантового дефекта

2019 ◽  
Vol 127 (11) ◽  
pp. 736
Author(s):  
А.С. Корнев ◽  
К.И. Суворов ◽  
В.Е. Чернов ◽  
И.В. Копытин ◽  
Б.А. Зон
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Density Functional ◽  
Ab Initio Methods ◽  
Test Results ◽  
Dft Methods ◽  
Functional Theory ◽  
Frequency Dependent ◽  
Quantum Defect Theory ◽  
Ab Initio And Dft

The quantum defect theory is used to test the accuracy of ab initio methods and density functional theory (DFT) in calculating the frequency-dependent polarizabilities of diatomic molecules. We confine ourselves to testing only those variants of these methods that are most accurate for calculating static polarizabilities. The test results show that one of the main errors of the ab initio and DFT methods is associated with inaccuracies in determining the energies of excited states, where frequency-dependent polarizabilities have resonance maxima.

scholarly journals Electronic Structure Benchmark Calculations of CO2 Fixing Elementary Chemical Steps in RuBisCO Using the Projector-Based Embedding Approach

2020 ◽  
Author(s):  
Oscar A. Douglas-Gallardo ◽  
Ian J. Shepherd ◽  
Simon Bennie ◽  
Kara Ranaghan ◽  
Adrian Mulholland ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Atmospheric Carbon Dioxide ◽  
Density Functional ◽  
Enzyme Reaction ◽  
Dft Methods ◽  
Carboxylase Activity ◽  
Bisphosphate Carboxylase ◽  
Carbon Carbon Bond ◽  
Reaction Energies

<div>Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) is the main enzyme involved in atmospheric carbon dioxide (CO<sub>2</sub>) fixation in the biosphere. This enzyme catalyses a set of five chemical steps that take place in the same active-site within magnesium (II) coordination sphere. Here, a set of electronic structure benchmark calculations have been carried out on a reaction path proposed by Gready <i>et al.</i> by means of the projector-based embedding approach. Activation and reaction energies for all main steps catalyzed by RuBisCO have been calculated at the MP2, SCS-MP2, CCSD and CCSD(T)/aug-cc-pVDZ and cc-pVDZ levels of theory. </div><div><br></div><div>The treatment of the magnesium cation with post-HF methods is explored to determine the nature of its involvement in the mechanism. With the high-level ab initio values as a reference, we tested the performance of a set of density functional theory (DFT) exchange-correlation (xc) functionals in reproducing the reaction energetics of RuBisCO carboxylase activity on a set of model fragments. Different DFT xc-functionals show large variation in activation and reaction energies. Activation and reaction energies computed at the B3LYP level are close to the reference SCS-MP2 results for carboxylation, hydration and protonation reactions.</div><div><br></div><div>However, for the carbon-carbon bond dissociation reaction, B3LYP and other functionals give results that differ significantly from the ab initio reference values. The results show the applicability of the projector-based embedding approach to metalloenzymes. This technique removes the uncertainty associated with the selection of different DFT xc-functionals and so can overcome some of inherent limitations of DFT calculations, complementing and potentially adding to modelling of enzyme reaction mechanisms with DFT methods.</div>

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