Net charges and valence AO's in the methylamines; the hydrogen basis set and the properties of nitrogen

1985 ◽  
Vol 63 (7) ◽  
pp. 1487-1491 ◽  
Author(s):  
Giuseppe Del Re ◽  
Sándor Fliszár ◽  
Michel Comeau ◽  
Claude Mijoule
Keyword(s):  
Basis Set ◽  
Basis Sets ◽  
Methyl Groups ◽  
Extended Form ◽  
Amine Nitrogen ◽  
Methyl Group ◽  
Net Charges ◽  
Extended Basis

Net charges and valence AO's for ammonia, methylamine, dimethylamine, and trimethylamine were calculated using extended basis sets. Superposition effects, evaluated by replacing Pople's standard 6-31G* basis by an extended form in which the basis of the ammonia H atoms and of the methyl groups of trimethylamine are retained in the treatment of each molecule, indicate that the quality of the treatment of amine nitrogen atoms is strongly dependent on the number of methyl groups. A new, augmented basis is proposed for the hydrogens, which appears to be reasonably well balanced: comparison with familiar (e.g., 6-31G*) calculations illustrates in what manner the treatment of nitrogen is worsened when even just one methyl group is replaced by hydrogen unless the impoverishment of the basis is suitably taken care of.

The effect of equi-molar dietary betaine and choline addition on performance and carcass quality of pigs

2001 ◽  
Vol 2001 ◽  
pp. 7-7
Author(s):  
H. Siljander-Rasi ◽  
K. Tiihonen ◽  
S. Peuranen ◽  
P.H. Simmins
Keyword(s):  
Diet Composition ◽  
Methyl Groups ◽  
Methyl Group ◽  
Feeding Level ◽  
Animal Feeding ◽  
Improved Performance ◽  
Pig Performance ◽  
Dietary Choline ◽  
Glycine Molecule

Betaine has three chemically reactive methyl groups attached to the nitrogen atom of the glycine molecule. Therefore, it can be used as a methyl group donor partially to replace methionine in poultry and pig diets. Recent work also suggests that betaine has an energy sparing role by reducing maintenance requirement of the pig (Schrama and Gerrits, 2000). Betaine has improved performance and carcass leanness in some studies but the results are variable and seem to depend on age and sex of the animal, feeding level and diet composition.Choline can also be used as methyl donor in animal feeds. In poultry, methyl groups are available after the conversion to betaine in the liver. However, dietary betaine is twice as efficient as the equi-molar dietary choline for increasing liver betaine levels in broiler chick (Saarinen et al., 2000). The aim of this study was to compare the response of pigs fed equi-molar betaine and choline in terms of pig performance and carcass characteristics.

Investigation of Some Sulphur Halides — An Application of the Pseudopotential Method

1983 ◽  
Vol 38 (4) ◽  
pp. 463-472
Author(s):  
T. Krüger ◽  
H. Preuß
Keyword(s):  
Significant Role ◽  
Density Functional ◽  
Correlation Energy ◽  
Basis Set ◽  
Pseudopotential Method ◽  
Basis Sets ◽  
Molecular Parameters ◽  
First Time ◽  
D Orbitals

Semilocal pseudopotentials are used in combination with a density-functional approximation for the correlation energy and special optimized basis sets to investigate the sulphur halides SF, SF2, SF3, FSSF, SSF2, SCl, SCl2, ClSSCl and SSCl2. It turns out that the inclusion of d-orbitals in the basis set playes a significant role with respect to the quality of the calculated molecular parameters. Properties of SF3 are calculated for the first time, and the differences between the disulphur difluorides and the disulphur dichlorides are explained.

The Rotational Barrier About the Disulphide Bridge in Dimethyl Disulphide: An Ab Initio Study

1984 ◽  
Vol 39 (5) ◽  
pp. 495-498
Author(s):  
V. Renugopalakrishnan ◽  
R. Walter
Keyword(s):  
Ab Initio ◽  
Rotational Barrier ◽  
Basis Set ◽  
Basis Sets ◽  
Disulphide Bridge ◽  
Minimal Basis ◽  
Gaussian Basis Sets ◽  
Type Function ◽  
Dimethyl Disulphide ◽  
Extended Basis

An ab initio molecular orbital technique was used to investigate the rotational barrier about the disulphide bridge in dimethyl disulphide. Various minimal and extended basis sets were used in the calculations. The chosen minimal basis set was the STO-3G set, and the extended basis sets were the STO 4-31G set, the Dunning and Hay set consisting of contracted Gaussian basis sets: [2s], [3s, 2p] and [6s, 4p] for H, C, and S atoms, and the Dunning and Hay basis set augmented with a d-type function on S atoms. The total energy was calculated as a function of the torsion angle about the disulphide bond. The barrier to rotation about this bond was found to be two-fold in nature, in accordance with previous findings. The heights of the barriers were observed to depend upon the basis set and input geometry. For our particular choice of basis sets and input geometry, the calculated value of the eis and trans barriers ranged from 12.68 to 16.49 kcal/mol and from 6.23 to 8 kcal/mol, respectively. Inclusion of a d-type function in the basis sets was found to result in better agreement between the calculated and experimental values, thereby emphasizing the need for considering 3d orbitals of sulphur in MO calculations

On the nature of the bonding in X-Be-O molecules (X = He, Ne, Ar)

1988 ◽  
Vol 53 (10) ◽  
pp. 2230-2238 ◽  
Author(s):  
Pavel Hobza ◽  
Paul von Ragué Schleyer
Keyword(s):  
Charge Transfer ◽  
Noble Gas ◽  
Basis Set ◽  
Basis Sets ◽  
Reverse Direction ◽  
Basis Set Superposition Error ◽  
Back Donation ◽  
Induction Energy ◽  
Extended Basis ◽  
Split Valence

The noble gas complexes, HeBeO, NeBeO, and ArBeO, discovered calculationally by Koch and Frenking, were reexamined at various theoretical levels. The results depended strongly on the size of the basis set but were insensitive to electron correlation corrections. The MP2 association energies of BeO with the noble gases, obtained with extended basis sets, were 4·80, 4·76, and 10·12 kcal/mol, respectively. The surprising stability of HeBeO (compared to NeBeO) is due to greater charge-transfer from He to BeO (donation) as well as to charge-transfer in the reverse direction (back donation). This compensates for the larger induction energy due to the greater polarizability of neon. The basis set superposition error is very large with split-valence basis sets; improvement of s and p function descriptions strongly reduces but does not completely eliminate this error.

THEORETICALLY EXPLORING METHYLATION EFFECTS ON SOLVATED MULTI-HYDROGEN BONDING AMMONIUM PERCHLORATE SYSTEMS

2004 ◽  
Vol 03 (02) ◽  
pp. 203-216 ◽  
Author(s):  
MIN-HSIEN LIU ◽  
CHENG CHEN ◽  
YAW-SHUN HONG
Keyword(s):  
Hydrogen Bonding ◽  
Ammonium Perchlorate ◽  
Density Functional ◽  
Basis Set ◽  
Ammonium Ion ◽  
Methyl Groups ◽  
Functional Theory ◽  
Methyl Group ◽  
The Relationship ◽  
Neighboring Bond

Methyl substituents are introduced into solvated ammonium perchlorate (AP) systems to explicate the effects of methylation on localized hydrogen-bonding. Methylation systems are modeled using density functional theory (DFT) B3LYP type with 4-31G(d, p), 6-311+(2d, p) basis set methods, indicating that whichever methyl group is substituted at the proton site in an ammonium ion or solvent, both methyl groups cease to H-bond, as evidence by elongation of the neighboring bond and characteristic red-shifts in the frequency of vibration. The energy barriers to the conversion from reactants to products in solvated AP systems are also discussed herein to help to elucidate the relationship solubility and H-bonding.

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>

A Comprehensive Computational Study on OCH+-Rg (Rg = He, Ne, Ar, Kr, Xe) Complexes

2003 ◽  
Vol 68 (3) ◽  
pp. 489-508 ◽  
Author(s):  
Yinghong Sheng ◽  
Jerzy Leszczynski
Keyword(s):  
Computational Study ◽  
Relativistic Effects ◽  
Dft Method ◽  
Basis Set ◽  
Rare Gas ◽  
Geometrical Parameters ◽  
Minor Effect ◽  
Dissociation Energies ◽  
Equilibrium Geometries

The equilibrium geometries, harmonic vibrational frenquencies, and the dissociation energies of the OCH+-Rg (Rg = He, Ne, Ar, Kr, and Xe) complexes were calculated at the DFT, MP2, MP4, CCSD, and CCSD(T) levels of theory. In the lighter OCH+-Rg (Rg = He, Ne, Ar) rare gas complexes, the DFT and MP4 methods tend to produce longer Rg-H+ distance than the CCSD(T) level value, and the CCSD-calculated Rg-H+ bond lengths are slightly shorter. DFT method is not reliable to study weak interaction in the OCH+-He and OCH+-Ne complexes. A qualitative result can be obtained for OCH+-Ar complex by using the DFT method; however, a higher-level method using a larger basis set is required for the quantitative predictions. For heavier atom (Kr, Xe)-containing complexes, only the CCSD method predicted longer Rg-H+ distance than that obtained at the CCSD(T) level. The DFT method can be applied to obtain the semiquantitative results. The relativistic effects are expected to have minor effect on the geometrical parameters, the H+-C stretching mode, and the dissociation energy. However, the dissociation energies are sensitive to the quality of the basis set. The nature of interaction between the OCH+ ion and Rg atoms was also analyzed in terms of the interaction energy components.

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.

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