THE ORIGIN OF THE ROTATIONAL BARRIER IN DIMETHYL ETHER AND DIMETHYL SULFIDE: A THEORETICAL STUDY

2007 ◽  
Vol 06 (03) ◽  
pp. 421-434 ◽  
Author(s):  
JÍMENEZ-FABIAN ◽  
A. F. JALBOUT
Keyword(s):  
Dimethyl Ether ◽  
Density Functional ◽  
Dimethyl Sulfide ◽  
Nbo Analysis ◽  
Rotational Barrier ◽  
Basis Sets ◽  
Functional Theory ◽  
Hartree Fock ◽  
Torsional Potential ◽  
Methyl Rotation

The torsional potential function for methyl rotation in dimethyl ether (DME) and dimethyl sulfide (DMS) has been determined by utilizing ab initio (Hartree–Fock and MP2) and density functional theory (B3LYP, B3P86, and B3PW91) methods along with several basis sets. Natural bond orbital (NBO) analysis was also applied to investigate the origin of the rotational barrier.

scholarly journals A Statistically Supported Antioxidant Activity DFT Benchmark—The Effects of Hartree–Fock Exchange and Basis Set Selection on Accuracy and Resources Uptake

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 5058
Author(s):  
Maciej Spiegel ◽  
Andrzej Gamian ◽  
Zbigniew Sroka
Keyword(s):  
Density Functional ◽  
Optimal Level ◽  
Basis Set ◽  
Basis Sets ◽  
Linear Regression Models ◽  
Functional Theory ◽  
Hartree Fock ◽  
Diffuse Function ◽  
Vertical Electron Affinity ◽  
High Level

Polyphenolic compounds are now widely studied using computational chemistry approaches, the most popular of which is Density Functional Theory. To ease this process, it is critical to identify the optimal level of theory in terms of both accuracy and resource usage—a challenge we tackle in this study. Eleven DFT functionals with varied Hartree–Fock exchange values, both global and range-separated hybrids, were combined with 14 differently augmented basis sets to calculate the reactivity indices of caffeic acid, a phenolic acid representative, and compare them to experimental data or a high-level of theory outcome. Aside from the main course, a validation of the widely used Janak’s theorem in the establishment of vertical ionization potential and vertical electron affinity was evaluated. To investigate what influences the values of the properties under consideration, linear regression models were developed and thoroughly discussed. The results were utilized to compute the scores, which let us determine the best and worst combinations and make broad suggestions on the final option. The study demonstrates that M06–2X/6–311G(d,p) is the best fit for such research, and, curiously, it is not necessarily essential to include a diffuse function to produce satisfactory results.

Nontemplate synthesis, characterization and theoretical study of tetraazamacrocycles

2012 ◽  
Vol 23 (1) ◽  
pp. 121-127
Author(s):  
İbrahim Șen ◽  
Cem Burak Yildiz ◽  
Akın Azizoğlu
Keyword(s):  
Density Functional ◽  
Basis Sets ◽  
Frontier Molecular Orbital ◽  
Spectroscopic Techniques ◽  
Functional Theory ◽  
Hartree Fock ◽  
H Nmr ◽  
Ft Ir ◽  
Molecular Electrostatic Potential Maps ◽  
C Nmr

Abstract The syntheses of new tetraaza macrocyclic compounds of variable ring sizes by non-template methods and their characterization with the help of elemental analysis and spectroscopic techniques (FT-IR, 1H-NMR, and 13C-NMR) have been reported in detail. The vibrational frequencies determined experimentally are compared with those obtained theoretically from density functional theory (DFT) and Hartree-Fock (HF) calculations. The comparisons between the experimental and theoretical results indicate that B3LYP level with both the 3-21G(d) and 6-31G+(d,p) basis sets is able to provide satisfactory results for predicting IR properties. The frontier molecular orbital diagrams and molecular electrostatic potential maps of title compounds have been also calculated and visualized at the B3LYP/6-31G+(d,p) level of theory.

scholarly journals Vibrational spectra of aniline in gas phase: An ab-initio study

2010 ◽  
Vol 7 (2) ◽  
pp. 449-455
Author(s):  
S. D. S. Chauhan ◽  
A.K. Sharma ◽  
R. Kumar ◽  
D. Kulshreshtha ◽  
R. Gupta ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Gas Phase ◽  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Ab Initio Study ◽  
Functional Theory ◽  
Hartree Fock ◽  
Modes Of Vibration ◽  
Experimental Findings

Vibrational frequencies of aniline in gas phase have been calculated and each of their modes of vibration assigned properly at RHF and DFT with 6-31G(d) basis set. In the present study, it has been observed that the 6-31G(d) basis set at both RHF and DFT levels of calculations provides better agreement to the experimental findings as compared to other basis sets. Simultaneously, Density functional theory is found to be superior to its counterpart Hartree Fock method.

scholarly journals Supramolecular study, Hirshfeld analysis and theoretical study of 6-methoxyquinolineN-oxide dihydrate

2013 ◽  
Vol 69 (6) ◽  
pp. 665-670 ◽  
Author(s):  
Rodolfo Moreno-Fuquen ◽  
Geraldine Hernandez ◽  
Alan R. Kennedy ◽  
Catriona A. Morrison
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Basis Sets ◽  
Water Molecules ◽  
Theoretical Studies ◽  
Functional Theory ◽  
Hartree Fock ◽  
Hirshfeld Surfaces ◽  
Hirshfeld Analysis ◽  
Oxide Group

In the crystal structure of 6-methoxyquinolineN-oxide dihydrate, C10H9NO2·2H2O, (I), the presence of two-dimensional water networks is analysed. The water molecules form unusual water channels, as well as two intersecting mutually perpendicular columns. In one of these channels, the O atom of theN-oxide group acts as a bridge between the water molecules. The other channel is formed exclusively by water molecules. Confirmation of the molecular packing was performed through the analysis of Hirshfeld surfaces, and (I) is compared with other similar isoquinoline systems. Calculations of bond lengths and angles by the Hartree–Fock method or by density functional theory B3LYP, both with 6-311++G(d,p) basis sets, are reported, together with the results of additional IR, UV–Vis and theoretical studies.

scholarly journals Coordination Behavior of Ni2+, Cu2+, and Zn2+ in Tetrahedral 1-Methylimidazole Complexes: A DFT/CSD Study

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Samuel Tetteh
Keyword(s):  
Density Functional ◽  
Population Analysis ◽  
Substantial Reduction ◽  
Nbo Analysis ◽  
Basis Sets ◽  
Dft Methods ◽  
Functional Theory ◽  
Formal Charge ◽  
Coordination Behavior ◽  
The Stability

The interaction between nickel (Ni2+), copper (Cu2+), and zinc (Zn2+) ions and 1-methylimidazole has been studied by exploring the geometries of eleven crystal structures in the Cambridge Structural Database (CSD). The coordination behavior of the respective ions was further investigated by means of density functional theory (DFT) methods. The gas-phase complexes were fully optimized using B3LYP/GENECP functionals with 6-31G∗ and LANL2DZ basis sets. The Ni2+ and Cu2+ complexes show distorted tetrahedral geometries around the central ions, with Zn2+ being a perfect tetrahedron. Natural bond orbital (NBO) analysis and natural population analysis (NPA) show substantial reduction in the formal charge on the respective ions. The interaction between metal d-orbitals (donor) and ligand orbitals (acceptor) was also explored using second-order perturbation of the Fock matrix. These interactions followed the order Ni2+ > Cu2+ > Zn2+ with Zn2+ having the least interaction with the ligand orbitals. Examination of the frontier orbitals shows the stability of the complexes in the order Ni2+ > Cu2+ < Zn2+ which is consistent with the Irving–Williams series.

AB INITIO AND DFT STUDY OF NON-COVALENT INTERACTIONS BETWEEN RARE GAS ATOMS AND AROMATIC RINGS

2013 ◽  
Vol 12 (03) ◽  
pp. 1350012 ◽  
Author(s):  
CHENG CHENG ◽  
MIN ZHANG ◽  
LI SHENG
Keyword(s):  
Ab Initio ◽  
Weak Interaction ◽  
Density Functional ◽  
Nbo Analysis ◽  
Basis Sets ◽  
Rare Gas ◽  
Aromatic Rings ◽  
Functional Theory ◽  
Rare Gas Atoms ◽  
Non Covalent Interactions

In this paper, the weak interaction between aromatic rings (ARs) and rare gas (Rg) atoms has been studied using ab initio calculation and density functional theory (DFT). The augmented Dunning basis sets were used, and the convergence test was performed up to aug-cc-pV5Z. Among the computationally feasible methods, ωB97XD performed the best for these non-covalent systems. NBO analysis was performed to investigate the nature of the Rg/AR interactions. In this type of weak interaction, the induced and instantaneous dipole and charge transfer character both contribute to the interaction energies and equilibrium distances.

scholarly journals Scaled quantum chemical studies of the structural and vibrational spectra of acetyl coumarin

2006 ◽  
Vol 4 (4) ◽  
Author(s):  
Khaled Bahgat
Keyword(s):  
Density Functional ◽  
Solid Phase ◽  
Normal Modes ◽  
Basis Sets ◽  
Functional Theory ◽  
Hartree Fock ◽  
Full Structure ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Ft Ir

AbstractThe solid phase FT-IR and FR-Raman spectra of acetyl coumarin have been recorded in the regions 4000–50 cm−1. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on density functional theory (DFT) and Hartree-Fock (HF) at 6–31G* and 6–311++G** basis sets. The resulting force fields were transformed to internal coordinates, the calculated vibrational frequencies and normal modes were utilized in the assignment of the observed vibrational fundamentals. The measured spectral data were used to refine the vibrational force constants by means of a small number of scaling factors.

scholarly journals Investigation of hydrogen bonding between nitrosamine and sulfuric acid using Density Functional Theory

2014 ◽  
Vol 25 (1) ◽  
pp. 5-10
Author(s):  
Sadeghali Bavafa ◽  
Mona Mahboubi
Keyword(s):  
Hydrogen Bonding ◽  
Density Functional ◽  
Natural Bond Orbital ◽  
Nbo Analysis ◽  
Basis Sets ◽  
Stable Complex ◽  
Antibonding Orbital ◽  
Functional Theory ◽  
Hydrogen Bonding Interactions ◽  
Density Transfer

Abstract DFT calculations were performed to analyze those interactions; B3LYP and B3PW91 methods were applied and the following basis sets were used: 6-311++G(2d, 2p), 6-311++G(3df, 3pd) and aug-cc-pVDZ. The natural bond orbital (NBO) analysis and atom in molecules (AIM) theory were applied to understand the nature of the interactions. The most stable complex NS1 with an eight-membered cyclic structure contains two O- H· ··O and N-H·· ·O hydrogen bonding interactions. From the values of r(r) at O·· ·H critical points, it can be concluded that the H-boding in eight-membered cyclic NS1 is stronger than other. The elongation of the O-H bond length is caused by the electron-density transfer to the O-H antibonding orbital.

POST HARTREE–FOCK AND DENSITY FUNCTIONAL THEORY STUDIES ON (BN)n=1–10 CLUSTERS

2005 ◽  
Vol 04 (03) ◽  
pp. 377-388 ◽  
Author(s):  
V. NIRMALA ◽  
P. KOLANDAIVEL
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Structural Parameters ◽  
Nbo Analysis ◽  
Simple Expression ◽  
Binding Energies ◽  
Basis Set ◽  
Functional Theory ◽  
Basis Set Superposition Error ◽  
Hartree Fock

Density functional theory and Møller–Plesset perturbation theory methods have been used to study the ring clusters of ( BN )n=1–10 employing 6-311++G** basis set. The binding energies have been corrected for the basis set superposition error (BSSE). Static polarizability of these ring clusters has been investigated. A simple expression for the size dependence of polarizability has been invoked, so that the same relation can be useful for predicting the polarizability of larger clusters. The topological properties were analyzed employing the Bader's atoms in molecules theory. A good correlation between the structural parameters and the properties of electron density is found. Localization and delocalization indices were also used for the analysis of molecular electronic structure by an electron pair perspective. The contribution of stereo electronic interactions to the molecular properties as a function of ring size is analyzed based on the natural bond orbital (NBO) analysis.

Computational chemistry applied to vibrational spectroscopy: A tool for characterization of nucleic acid bases and some of their 5-substituted derivatives

2017 ◽  
Vol 2 (8) ◽  
Author(s):  
M. Alcolea Palafox
Keyword(s):  
Solid State ◽  
Nucleic Acid ◽  
Computational Chemistry ◽  
Vibrational Spectroscopy ◽  
Density Functional ◽  
Basis Sets ◽  
Nucleic Acid Bases ◽  
Functional Theory ◽  
Hartree Fock

Abstract Computational chemistry can be applied to vibrational spectroscopy in different ways, such as for a better characterization and assignment of all the bands of the experimental spectra, as a tool in the identification of the tautomers present in the gas phase and in the solid state through their spectra and for the simulation of the solid and liquid phase of a compound and the consequent simulation and interpretation of their spectra. In the present study, as an example of the applicability of computational chemistry, the structure and spectra of cytosine and uracil nucleic acid bases and two cytosine derivatives are shown. The FTIR and Raman spectra were analysed with the support of ab initio (Hartree-Fock (HF), MP2) and density functional theory (DFT) (B3LYP, PBE, B-P, etc.) calculations using several basis sets and several scaling equations. The calculations predict an easier tautomerization of cytosine than uracil molecule, but the tautomerization is hindered in the 5-bromocytosine molecule. Thus, in the solid state, this molecule only exists in the amino-oxo tautomeric form.

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