Metal and Ligand Effects on Coordinated Methane pKa. Direct Correlation with the Methane Activation Barrier

10.26434/chemrxiv.12323726 ◽

2020 ◽

Author(s):

Amy Guan ◽

Ivy Liang ◽

Christopher Zhou ◽

Thomas Cundari

Keyword(s):

Free Energy ◽

Direct Relationship ◽

Activation Barrier ◽

Methane Activation ◽

Coupled Cluster ◽

Activation Barriers ◽

Ligand Effects ◽

3D Metals ◽

Cluster Methods ◽

The Impact

DFT and coupled cluster methods were used to investigate the impact of 3d metals and ligands upon the acidity and activation of coordinated methane C–H bonds. A strong, direct relationship was established between the pKa of coordinated methane and the subsequent free energy barriers to H3C–H activation. The few outliers to this relationship indicated other factors– such as thermodynamic stability of the product and ligand-metal coordination type – also impacted the methane activation barrier (dG‡). High variations in the activation barriers and pKa values were found with a range of 34.8 kcal/mol for the former and 28.6 pKa units for the latter. Clear trends among specific metals and ligands were also derived; specific metals, such as CoI, as well as Lewis and p-acids consistently yielded higher acidity for the ligated methane and hence lower dG‡.

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Metal and Ligand Effects on Coordinated Methane pKa: Direct Correlation with the Methane Activation Barrier

The Journal of Physical Chemistry A ◽

10.1021/acs.jpca.0c04756 ◽

2020 ◽

Vol 124 (36) ◽

pp. 7283-7289 ◽

Cited By ~ 1

Author(s):

Amy S. Guan ◽

Ivy X. Liang ◽

Christopher X. Zhou ◽

Thomas R. Cundari

Keyword(s):

Activation Barrier ◽

Methane Activation ◽

Ligand Effects

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Lowering the C-H Bond Activation Barrier of Methane Using SAC@Cu(111): A Periodic DFT Investigations

10.33774/chemrxiv-2021-zfrcn ◽

2021 ◽

Author(s):

Meema Bhati ◽

Jignesh Dhumal ◽

Kavita Joshi

Keyword(s):

Density Functional ◽

Bond Activation ◽

Activation Barrier ◽

Bond Cleavage ◽

Minimum Energy ◽

Value Added ◽

Methane Activation ◽

Single Atom ◽

Activation Barriers ◽

Metal Doped

Methane has long captured the world's spotlight for being the simplest and yet one of the most notorious hydrocarbon. Exploring its potential to be converted into value added products has raised a compelling interest. In the present work, we have studied the efficiency of Single-Atom Catalysts (SACs) for methane activation employing Density Functional Theory (DFT). The Climbing Image-Nudged Elastic Bond (CI-NEB) method is used in tandem with the Improved Dimer (ID) method to determine the minimum energy pathway for the first C-H bond dissociation of methane. Our study reported that the transition-metal doped Cu(111) surfaces enhance adsorption, activate C-H bond, and reduce activation barrier for first C-H bond cleavage of methane. The results suggest Ru/Co/Rh doped Cu(111) as promising candidates for methane activation with minimal activation barrier and less endothermic reaction. For these SACs, the calculated activation barriers for first C-H bond cleavage are 0.17 eV, 0.24 eV, and 0.26 eV respectively, which is substantially lower than 1.13 eV, the activation barrier for Cu(111).

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Free energies and mechanisms of water exchange around Uranyl from first principles molecular dynamics

MRS Proceedings ◽

10.1557/opl.2012.181 ◽

2012 ◽

Vol 1383 ◽

Cited By ~ 4

Author(s):

Raymond Atta-Fynn ◽

Eric J. Bylaska ◽

Wibe A. de Jong

Keyword(s):

Free Energy ◽

Density Functional ◽

Water Exchange ◽

Activation Barrier ◽

Hydration Number ◽

Bulk Water ◽

Water Dissociation ◽

Free Energies ◽

Activation Barriers ◽

Hydration Shells

ABSTRACTFrom density functional theory (DFT) based ab initio (Car-Parrinello) metadynamics, we compute the activation energies and mechanisms of water exchange between the first and second hydration shells of aqueous Uranyl (UO22+) using the primary hydration number of U as the reaction coordinate. The free energy and activation barrier of the water dissociation reaction [UO2(OH2)5]2+(aq) → [UO2(OH2)4]2+(aq) + H2O are 0.7 kcal and 4.7 kcal/mol respectively. The free energy is in good agreement with previous theoretical (-2.7 to +1.2 kcal/mol) and experimental (0.5 to 2.2 kcal/mol) data. The associative reaction [UO2(OH2)5]2+(aq) + H2O → [UO2(OH2)6]2+(aq) is short-lived with a free energy and activation barrier of +7.9 kcal/mol and +8.9 kca/mol respectively; it is therefore classified as associative-interchange. On the basis of the free energy differences and activation barriers, we predict that the dominant exchange mechanism between [UO2(OH2)5]2+(aq) and bulk water is dissociative.

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Organizational Justice and Employee Sustainability: The Mediating Role of Organizational Commitment

SEISENSE Journal of Management ◽

10.33215/sjom.v3i3.334 ◽

2020 ◽

Vol 3 (3) ◽

pp. 12-22

Author(s):

Mehreen Fatima ◽

Zeeshan Izhar ◽

Zaheer Abbas Kazmi

Keyword(s):

Organizational Commitment ◽

Organizational Justice ◽

Developing Country ◽

Design Methodology ◽

Direct Relationship ◽

Banking Sector ◽

Mediating Role ◽

Research Gap ◽

The Impact

Purpose- The primary purpose of the study is to determine the impact of organizational justice (OJ) on employee sustainability. Along with that, it also describes how organizational commitment mediates this direct relationship. This study includes all dimensions of OJ which are distributive, procedural and interactional (interpersonal & informational) within the context of a developing country (Pakistan). Design/Methodology- This study has considered employees working in the banking sector of Pakistan. Two hundred ten questionnaires were received back from employees. Regression analysis was used to analyze direct relationships between variables, while smart partial least squares (PLS) were used for mediation analysis. Findings- Results demonstrated that all hypothesis were accepted and it was also confirmed that organizational commitment (OC) mediates the direct relationship between OJ and employee sustainability (ES). Originality/value- Multidimensional construct of organizational justice was tested in this study, in the context of a developing country (Pakistan), to address the research gap.

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The X40x10 Halogen Bonding Benchmark Revisited: Surprising Importance of (n-1)d Subvalence Correlation

10.26434/chemrxiv.5580007.v1 ◽

2017 ◽

Author(s):

Manoj Kumar Kesharwani ◽

Nitai Sylvetsky ◽

Debashree Manna ◽

Jan M.L. Martin

Keyword(s):

Dissociation Energy ◽

Noncovalent Interactions ◽

Halogen Bonding ◽

Coupled Cluster ◽

Dissociation Energies ◽

Iodine Species ◽

Explicitly Correlated ◽

High Level ◽

Cluster Methods ◽

Small Separation

We have re-evaluated the X40x10 benchmark for halogen bonding using conventional and explicitly correlated coupled cluster methods. For the aromatic dimers at small separation, improved CCSD(T)–MP2 “high-level corrections” (HLCs) cause substantial reductions in the dissociation energy. For the bromine and iodine species, (n-1)d subvalence correlation increases dissociation energies, and turns out to be more important for noncovalent interactions than is generally realized. As in previous studies, we find that the most efficient way to obtain HLCs is to combine (T) from conventional CCSD(T) calculations with explicitly correlated CCSD-F12–MP2-F12 differences.

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Double Precision Is Not Needed for Many-Body Calculations: New Conventional Wisdom

10.26434/chemrxiv.6104804.v1 ◽

2018 ◽

Author(s):

Pavel Pokhilko ◽

Evgeny Epifanovsky ◽

Anna I. Krylov

Keyword(s):

Large Scale ◽

Computation Time ◽

Coupled Cluster ◽

Double Precision ◽

Many Body ◽

Single Precision ◽

Parallel Performance ◽

Point Representation ◽

Electron Repulsion Integrals ◽

Cluster Methods

Using single precision floating point representation reduces the size of data and computation time by a factor of two relative to double precision conventionally used in electronic structure programs. For large-scale calculations, such as those encountered in many-body theories, reduced memory footprint alleviates memory and input/output bottlenecks. Reduced size of data can lead to additional gains due to improved parallel performance on CPUs and various accelerators. However, using single precision can potentially reduce the accuracy of computed observables. Here we report an implementation of coupled-cluster and equation-of-motion coupled-cluster methods with single and double excitations in single precision. We consider both standard implementation and one using Cholesky decomposition or resolution-of-the-identity of electron-repulsion integrals. Numerical tests illustrate that when single precision is used in correlated calculations, the loss of accuracy is insignificant and pure single-precision implementation can be used for computing energies, analytic gradients, excited states, and molecular properties. In addition to pure single-precision calculations, our implementation allows one to follow a single-precision calculation by clean-up iterations, fully recovering double-precision results while retaining significant savings.

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A computational study for the reaction mechanism of metal-free cyanomethylation of aryl alkynoates with acetonitrile

RSC Advances ◽

10.1039/d1ra01649k ◽

2021 ◽

Vol 11 (30) ◽

pp. 18246-18251

Author(s):

Selçuk Eşsiz

Keyword(s):

Density Functional Theory ◽

Reaction Mechanism ◽

Density Functional ◽

Computational Study ◽

Coupled Cluster ◽

Functional Theory ◽

Metal Free ◽

Coupled Cluster Methods ◽

High Level ◽

Cluster Methods

A computational study of metal-free cyanomethylation and cyclization of aryl alkynoates with acetonitrile is carried out employing density functional theory and high-level coupled-cluster methods, such as [CCSD(T)].

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