Ab Initio MO-MD Simulation Based on the Fragment MO Method. A Case of (−)-Epicatechin Gallate with STO-3G Basis Set

2008 ◽  
Vol 81 (1) ◽  
pp. 110-112 ◽  
Author(s):  
Katsuhiro Tamura ◽  
Toshio Watanabe ◽  
Takayoshi Ishimoto ◽  
Umpei Nagashima
Keyword(s):  
Ab Initio ◽  
Md Simulation ◽  
Basis Set ◽  
Epicatechin Gallate ◽  
Simulation Based ◽  
Ab Initio Mo

Computational Procedure of Lattice Energy Using the Ab Initio MO Method

2003 ◽  
Vol 02 (02) ◽  
pp. 233-244 ◽  
Author(s):  
Kanade Nagayoshi ◽  
Tohru Ikeda ◽  
Kazuo Kitaura ◽  
Shigeru Nagase
Keyword(s):  
Ab Initio ◽  
Molecular Crystals ◽  
Lattice Energy ◽  
Computational Procedure ◽  
Basis Set ◽  
Full Account ◽  
Packing Structure ◽  
Donor Acceptor ◽  
Ab Initio Mo ◽  
Experimental Values

Recently, we have proposed a computational procedure for calculations of lattice energies of molecular crystals using the ab initio MO method. This procedure does not use potential functions and is applicable to a variety of molecular crystals. The procedure has been successfully applied to calculation of packing structure of electron donor-acceptor complex, H3N–BF3, and hydrogen bonding crystal, CH3OH. In this work, we present a full account of the computational procedure. This method is applied to the packing structure calculations of hydrocarbon crystals, C2H2, C2H4 and C6H6. The lattice parameters optimized at the MP2/6-311++G** level are in good agreement with the experimental values. The basis set dependence of the lattice constants is also discussed for several crystals.

Sulfonamidyls, 4. Ab Initio MO Calculations on Sulfonyl and Carbonyl Substituted Aminyl Radicals

1981 ◽  
Vol 36 (2) ◽  
pp. 279-281 ◽  
Author(s):  
Herman Teeninga ◽  
Wim C. Nieuwpoort ◽  
Jan B. F. N. Engberts
Keyword(s):  
Ab Initio ◽  
Hyperfine Splitting ◽  
Relative Magnitude ◽  
Basis Set ◽  
Mo Calculations ◽  
Aminyl Radicals ◽  
Ab Initio Mo Calculations ◽  
Double Zeta ◽  
Double Zeta Basis ◽  
Ab Initio Mo

Abstract The relative magnitude of the nitrogen hyperfine splitting constants of sulfonamidyls and carboxamidyls is rationalized in terms of the results of ab initio MO calculations using the "double zeta" basis set of Roos and Siegbahn.

Orbital interactions. XII. Product studies and competition kinetic measurements of the Birch reduction of a series of hexahydrodimethanonaphthalenes and their interpretation in terms of orbital interactions through space and through bonds

1983 ◽  
Vol 36 (12) ◽  
pp. 2423 ◽  
Author(s):  
DD Chau ◽  
MN Paddon-Row ◽  
HK Patney
Keyword(s):  
Ab Initio ◽  
Anion Radical ◽  
Basis Set ◽  
Mo Calculations ◽  
Birch Reduction ◽  
Symmetry Constraint ◽  
Orbital Interactions ◽  
Ab Initio Mo Calculations ◽  
Ab Initio Mo ◽  
Anion Radicals

Relative rate constants for the Birch reduction (Li/liq. NH3/ButOH) of the three isomeric hexahydrodimethanonaphthalenes (3)-(5) and the octahydro analogues (10)-(13) were obtained and compared with those obtained for the reduction of norbornadiene and norbornene from an earlier study. Diene (5) was reduced almost 2000 times more rapidly than norbornene and 20000 times more rapidly than the monoene (13). Rate-enhancement factors for dienes (3) and (4) were less substantial but meaningful: 19 for (3) [compared with (10)] and 35 for (4) [compared with (12)]. These rate enhancements were attributed to the operation of π* orbital interactions through space in diene (5) and to the presence of π* orbital interactions through four bonds in dienes (3) and (4). The existence of a linear relationship between the natural logarithm of the rate of reduction of a substrate and its LUMO energy (obtained from either gas-phase electron affinities or ab initio MO calculations) supports this conclusion. The only-fair correlation of the above relationship was attributed to the neglect of other factors, such as the electronic structure and the geometry of the anion radical, which contribute to the overall rate of the Birch reduction. These two factors were explored by using PMO theory and ab initio MO calculations. In particular, full geometry optimizations (UHF, STO-3G basis set) on the anion radicals of norbornadiene (1) (C2v symmetry constraint) and norbornene (22) (Cs symmetry constraint) were carried out, and their geometries reported. Noteworthy is the strong pyramidalization of the olehic centres of (1) and (22) in the endo direction. These pyramidalizations explain the observed stereoselective exo protonation of the anion radical of (1), and also the much faster rate of reduction of (1) compared with (5), since the pyramidalization in the anion radical of (5) is such as to hinder protonation. The geometries of anion radicals appear to have a profound effect on rates, on stereoselectivity of protonation, and on the structures of the final products, and this is discussed in detail. The synthesis of the diene (3) is also described.

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

Sign in / Sign up

Export Citation Format

Share Document