scholarly journals Ab initio post-HF CCSD(T) Calculations for Triplet and Singlet Methylene in Four consecutive Dunning Basis Sets with Extrapolations to Infinite Limits for Various Molecular Properties

2005 ◽  
Vol 6 (1) ◽  
pp. 157-176 ◽  
Author(s):  
Alexander Neugebauer ◽  
Günter Häfelinger
Keyword(s):  
Ab Initio ◽  
Molecular Properties ◽  
Basis Sets ◽  
Singlet Methylene

On the Electric Dipole (hyper)polarizability of Difluorodiacetylene (F-C≡C-C≡C-F)

2006 ◽  
Vol 2 (1-2) ◽  
pp. 15-19 ◽  
Author(s):  
G. Maroulis
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Molecular Properties ◽  
Basis Sets ◽  
Dipole Polarizability ◽  
Functional Theory ◽  
Consistent Field ◽  
B3lyp Method ◽  
Self Consistent ◽  
Self Consistent Field

We report static dipole polarizability and hyperpolarizability values difluoroacetylene obtained from finite-field density functional theory and conventional ab initiocalculations with especially designed flexible basis sets of Gaussian-type functions. Our results show that electron correlation has a small effect on the dipole polarizability but a strong one on the hyperpolarizability. The widely used B3LYP method yields molecular properties fairly close to the ab initio ones. The effect of the fluorination on the molecular properties is quite obvious at the self-consistent field level of theory: ᾱ (FCCCCF) < ᾱ (HCCCCF) < ᾱ (HCCCCH) and γ̄ (FCCCCF) < γ̄ (HCCCCF) < γ̄ (HCCCCH).

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

Ab Initio Study of the Stability of the Ylide-like Intermediate Methyleneoxonium in the Reaction between Singlet Methylene and Water

1996 ◽  
Vol 118 (23) ◽  
pp. 5408-5411 ◽  
Author(s):  
Carlos Gonzalez ◽  
Albeiro Restrepo-Cossio ◽  
Manuel Márquez ◽  
Kenneth B. Wiberg
Keyword(s):  
Ab Initio ◽  
Ab Initio Study ◽  
The Stability ◽  
Singlet Methylene
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