scholarly journals Energy maxima in anionic nucleophilic additions to carbonyl groups: The location of a saddle point for the addition of hydride to formaldehyde

1988 ◽  
Vol 66 (1) ◽  
pp. 149-154 ◽  
Author(s):  
C. I. Bayly ◽  
F. Grein
Keyword(s):  
Electron Correlation ◽  
Nucleophilic Addition ◽  
Major Change ◽  
Energy Difference ◽  
Basis Set ◽  
Basis Sets ◽  
Attractive Potential ◽  
Energy Curve ◽  
Energy Maximum ◽  
Reaction Profile

The reaction profile of the anionic nucleophilic addition of hydride to formaldehyde giving methanolate was re-investigated using theoretical ab initio methods. A variety of basis sets (including 4-31G and 6-31G with and without polarization and diffuse functions) were used, and electron correlation calculations were performed at the MP2, MP3, and MP4 levels with geometry optimizations at the MP2 level. Upon the addition of diffuse functions to the basis set, a local energy maximum was introduced into the SCF reaction profile, a major change in the character of the profile compared to the entirely attractive potential energy curve found in previous studies. On the reactants side of the barrier a local minimum 4.56 kcal/mol lower in energy was found, corresponding to an ion–dipole complex. With the inclusion of electron correlation, the local barrier almost disappeared, with the energy difference between the ion–dipole complex and the barrier maximum decreasing to less than 1 kcal/mol. Furthermore, the location of the energy maximum along the reaction coordinate changed by 0.4 Å. These results are used to critically re-evaluate some prevalent viewpoints on the nature of the reaction profiles of this type of anionic nucleophilic addition.

Alkyl versus hydrogen substitution: an abinitio study of the addition of hydroxide to formaldehyde and to acetone

1989 ◽  
Vol 67 (1) ◽  
pp. 176-182 ◽  
Author(s):  
C. I. Bayly ◽  
F. Grein
Keyword(s):  
Quantum Chemical Study ◽  
Chemical Study ◽  
Energy Difference ◽  
Basis Set ◽  
Secondary Minimum ◽  
Energy Curve ◽  
Co Addition ◽  
Hydrogen Substitution ◽  
Acetone System ◽  
Reaction Profile

The reaction profiles of the anionic nucleophilic addition of hydroxide to formaldehyde (system I) and to acetone (system II) were studied using theoretical abinitio methods. Calculations were carried out using the 4-31G basis set augmented with polarization and diffuse functions on some atoms. Electron correlation calculations were performed at the MP2 (frozen core), MP2, and MP4 levels for system I and at the MP2 (frozen core) level for system II. For both systems a local energy maximum was found at a C—OH distance of 2.5 Å. The barrier maximum was at lower energy than the separated reactants (−17.2 kcal/mol for system I and −5.6 kcal/mol for system II). This type of reaction profile is in accordance with a previous study on a prototype reaction. The energy difference between the barrier maximum and the secondary minimum (towards the reactants) was very small for system I (0.7 kcal/mol), but higher for system II (5.4 kcal/mol). The geometries of the two systems differed significantly in the region of the reaction coordinate containing the barrier and the secondary minimum. Keywords: quantum chemical study, addition of OH− to H2CO, addition of OH− to (CH3)2CO, alkyl versus hydrogen substitution, potential energy curve.

Potential energy curve of N2 revisited

2011 ◽  
Vol 76 (4) ◽  
pp. 327-341 ◽  
Author(s):  
Vladimír Špirko ◽  
Xiangzhu Li ◽  
Josef Paldus
Keyword(s):  
Potential Energy ◽  
Chem Phys ◽  
Nitrogen Molecule ◽  
Basis Set ◽  
Basis Sets ◽  
Energy Curve ◽  
Vibrational Levels ◽  
Complete Basis Set ◽  
State Potential ◽  
Excellent Description

Recently generated ground state potential energy curves (PECs) for the nitrogen molecule, as obtained with the reduced multireference (RMR) coupled-cluster (CC) method with singles and doubles (RMR-CCSD), and its version corrected for the secondary triples RMR-CCSD(T), using cc-pVXZ basis sets with X = D, T, and Q, as well as the extrapolated complete basis set (cbs) limit (X. Li and J. Paldus: J. Chem. Phys. 2008, 129, 054104), are compared with both the highly accurate theoretical configuration interaction PEC of Gdanitz (Chem. Phys. Lett. 1998, 283, 253) and analytic PECs obtained by fitting an extensive set of experimental data (R. J. Le Roy et al.: J. Chem. Phys. 2006, 125, 164310). These results are analyzed using a morphing procedure based on the reduced potential curve (RPC) method of Jenč. It is found that an RPC fit of both theoretical potentials can be achieved with only a few parameters. The RMR PECs are found to provide an excellent description of experimentally available vibrational levels, but significantly deviate from those of Gdanitz’s PEC for highly stretched geometries, yet still do provide a qualitatively correct PECs that lie within the region delimited by Le Roy’s analytical PECs.

Ab initio studies of isocyanatoborane and difluoroisocyanatoborane; bent or linear BNCO chains?

1991 ◽  
Vol 69 (6) ◽  
pp. 1000-1005 ◽  
Author(s):  
Susan Ellis ◽  
Edward G. Livingstone ◽  
Nicholas P. C. Westwood
Keyword(s):  
Carbon Atom ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Potential Surface ◽  
Energy Difference ◽  
Basis Set ◽  
Basis Sets ◽  
Hartree Fock ◽  
Split Valence ◽  
Valence Basis Set

Ab initio calculating at the 3-21G, 6-31G*, 6-31G**, 6-311G*, and 6-311G** Hartree–Fock levels, have been performed on the unknown H2BNCO and F2BNCO molecules in order to establish the geometries of these isoelectronic propadienone analogues. For H2BNCO the double split valence basis sets lead to linear BNCO chains, whereas either a triple split valence basis set, or the inclusion of correlation to second order (MP2/6-31G*) gives trans-bent structures. These have angles at nitrogen of 153.6° (6-311G*) or 149.9° (MP2/6-31G*), with the potential surface for angle bending extremely flat, and 0.5 kJ mol−1 (6-311 G*) or 1.12 kJ mol−1 (MP2/6-31 G*) separating the C2v and Cs structures. For the bent structures there is a small trans-bend (4–6°) at the carbon atom. The F2BNCO molecule is also linear at the 3-21G level, but is, however, already trans-bent (145.6° at nitrogen, 175.9° at carbon) at the 6-31G* Hartree–Fock level; 1.47 kJ mol−1 separates the bent and linear structures. The triple split valence basis set 6-311G* leads to a further decrease in the angle at nitrogen (141.0°), and a similar NCO angle (175.9°), with the bent structure favoured by 3.85 kJ mol−1. MP2/6-31G* calculations give a minimum with an angle at nitrogen of 140.2°, and a bent-linear energy difference of 3.58 kJ mol−1. Key words: ab initio calculations, isocyanatoboranes, structures, quasilinearity, propadienone analogues.

scholarly journals Extrapolation of Atomic Natural Orbitals of basis set to complete basis set limit

2017 ◽  
Vol 10 (2) ◽  
pp. 159-164
Author(s):  
Jaroslav Granatier
Keyword(s):  
Electron Correlation ◽  
Quantitative Agreement ◽  
Basis Set ◽  
Basis Sets ◽  
Natural Orbitals ◽  
Benchmark Data ◽  
Complete Basis ◽  
Complete Basis Set ◽  
Complete Basis Set Limit ◽  
Atomic Natural Orbitals

AbstractRelativistic Atomic Natural Orbitals (ANO-RCC) are extrapolated to the complete basis set limit. ANO-RCC-VXZP (X = D, T, Q) basis sets were extrapolated using standard extrapolation techniques. Five noncovalent complexes, characterized by hydrogen, dispersion and halogen interactions, were chosen. Accurate description of the studied complexes is allowed only after the inclusion of electron correlation and large basis sets which have to include polarization and diffuse functions. Results are in quantitative agreement with the benchmark data obtained by standard aug-cc-pVXZ-DK (X = D, T, Q) basis sets considering chemical accuracy of ±1 kcal/mol.

scholarly journals THE INTERACTION OF Co2+-AMMONIA MODELLING: THE COMPARATIVE STUDY BETWEEN AB INITIO AND ELECTRON CORRELATION METHODS

2010 ◽  
Vol 2 (2) ◽  
pp. 67-73
Author(s):  
Harno Dwi Pranowo ◽  
Foliatini Foliatini ◽  
Karna Wijaya
Keyword(s):  
Charge Transfer ◽  
Comparative Study ◽  
Electron Correlation ◽  
Transfer Effect ◽  
Basis Set ◽  
Basis Sets ◽  
Complex Energy ◽  
Hartree Fock ◽  
Correlation Methods ◽  
The Comparative Study

Research on comparison between Hartree-Fock method and electron correlation methods as well as the effect of size of basis sets on representing interaction of Co2+-NH3 observed from complex energy parameters and optimum geometric parameters have been carried out.The first step is screening basis sets based on charge transfer effect and BSSE value. The selected basis set does not yield charge transfer at 1,4 Å  

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

DFT Benchmark Study of the O--O Bond Dissociation Energy in Peroxides Validated with High-Level Ab-Initio Calculations

2019 ◽  
Author(s):  
Danilo Carmona ◽  
Pablo Jaque ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Reference Value ◽  
Basis Set ◽  
Basis Sets ◽  
Mean Deviation ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
The Mean ◽  
Experimental Values ◽  
High Level ◽  
Almost All

<div><div><div><p>Peroxides play a central role in many chemical and biological pro- cesses such as the Fenton reaction. The relevance of these compounds lies in the low stability of the O–O bond which upon dissociation results in radical species able to initiate various chemical or biological processes. In this work, a set of 64 DFT functional-basis set combinations has been validated in terms of their capability to describe bond dissociation energies (BDE) for the O–O bond in a database of 14 ROOH peroxides for which experimental values ofBDE are available. Moreover, the electronic contributions to the BDE were obtained for four of the peroxides and the anion H2O2− at the CBS limit at CCSD(T) level with Dunning’s basis sets up to triple–ζ quality provid- ing a reference value for the hydrogen peroxide anion as a model. Almost all the functionals considered here yielded mean absolute deviations around 5.0 kcal mol−1. The smallest values were observed for the ωB97 family and the Minnesota M11 functional with a marked basis set dependence. Despite the mean deviation, order relations among BDE experimental values of peroxides were also considered. The ωB97 family was able to reproduce the relations correctly whereas other functionals presented a marked dependence on the chemical nature of the R group. Interestingly, M11 functional did not show a very good agreement with the established order despite its good performance in the mean error. The obtained results support the use of similar validation strategies for proper prediction of BDE or other molecular properties by DF Tmethods in subsequent related studies.</p></div></div></div>

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

AlN Nanotubes: A DFT Study of Al-27 and N-14 Electric Field Gradient Tensors

2007 ◽  
Vol 62 (12) ◽  
pp. 711-715 ◽  
Author(s):  
Ahmad Seif ◽  
Mahmoud Mirzaei ◽  
Mehran Aghaie ◽  
Asadollah Boshra
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Density Functional ◽  
Quadrupole Coupling Constant ◽  
Basis Set ◽  
Basis Sets ◽  
B3lyp Method ◽  
Package Program ◽  
Nqr Parameters

Density functional theory (DFT) calculations were performed to calculate the electric field gradient (EFG) tensors at the sites of aliminium (27Al) and nitrogen (14N) nuclei in an 1 nm of length (6,0) single-walled aliminium nitride nanotube (AlNNT) in three forms of the tubes, i. e. hydrogencapped, aliminium-terminated and nitrogen-terminated as representatives of zigzag AlNNTs. At first, each form was optimized at the level of the Becke3,Lee-Yang-Parr (B3LYP) method, 6-311G∗∗ basis set. After, the EFG tensors were calculated at the level of the B3LYP method, 6-311++G∗∗ and individual gauge for localized orbitals (IGLO-II and IGLO-III) types of basis sets in each of the three optimized forms and were converted to experimentally measurable nuclear quadrupole resonance (NQR) parameters, i. e. quadrupole coupling constant (qcc) and asymmetry parameter (ηQ). The evaluated NQR parameters revealed that the considered model of AlNNT can be divided into four equivalent layers with similar electrostatic properties.With the exception of Al-1, all of the three other Al layers have almost the same properties, however, N layers show significant differences in the magnitudes of the NQR parameters in the length of the nanotube. Furthermore, the evaluated NQR parameters of Al-1 in the Al-terminated form and N-1 in the N-terminated form revealed the different roles of Al (base agent) and of N (acid agent) in AlNNT. All the calculations were carried out using the GAUSSIAN 98 package program.

scholarly journals The S66 Non-Covalent Interactions Benchmark Reconsidered Using Explicitly Correlated Methods Near the Basis Set Limit

2018 ◽  
Vol 71 (4) ◽  
pp. 238 ◽  
Author(s):  
Manoj K. Kesharwani ◽  
Amir Karton ◽  
Nitai Sylvetsky ◽  
Jan M. L. Martin
Keyword(s):  
Computational Cost ◽  
The Other ◽  
Basis Set ◽  
Basis Sets ◽  
Explicitly Correlated ◽  
Non Covalent Interactions ◽  
Explicitly Correlated Methods ◽  
The One ◽  
High Level ◽  
Covalent Interactions

The S66 benchmark for non-covalent interactions has been re-evaluated using explicitly correlated methods with basis sets near the one-particle basis set limit. It is found that post-MP2 ‘high-level corrections’ are treated adequately well using a combination of CCSD(F12*) with (aug-)cc-pVTZ-F12 basis sets on the one hand, and (T) extrapolated from conventional CCSD(T)/heavy-aug-cc-pV{D,T}Z on the other hand. Implications for earlier benchmarks on the larger S66×8 problem set in particular, and for accurate calculations on non-covalent interactions in general, are discussed. At a slight cost in accuracy, (T) can be considerably accelerated by using sano-V{D,T}Z+ basis sets, whereas half-counterpoise CCSD(F12*)(T)/cc-pVDZ-F12 offers the best compromise between accuracy and computational cost.

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