scholarly journals Molecular structure, enthalpies of formation and dissociation energies of the O – N bond for a number of aliphatic nitrates and nitrites

2021 ◽  
Vol 2052 (1) ◽  
pp. 012010
Author(s):  
D L Egorov ◽  
G M Khrapkovskii
Keyword(s):  
Molecular Structure ◽  
Experimental Data ◽  
Density Functional ◽  
Aliphatic Alcohols ◽  
Basis Sets ◽  
Enthalpies Of Formation ◽  
Homolytic Cleavage ◽  
Composite Method ◽  
Dissociation Energies

Abstract The optimal conformations of nitrates and nitrites of aliphatic alcohols C1-C4, as well as radicals formed during homolytic cleavage of O-NO2 and O-NO bonds were determined using the multistep (composite) method G4, as well as a large number of different density functional (DDF) methods and basis sets. The enthalpies of formation and dissociation energies of breaking bonds were calculated for the studied compounds. Comparison with the available experimental data shows that the best agreement with experiment is achieved when using the G4 method. In this case, the error in the enthalpies of formation does not exceed 1 kcal/mol. The paper also discusses the features of the influence of the molecular structure on the change in the series of enthalpies of formation and dissociation energies.

scholarly journals Basis Set Effects in the Description of the Cl-O Bond in ClO and XClO/ClOX Isomers (X = H, O, and Cl) Using DFT and CCSD(T) Methods

2019 ◽  
Vol 2019 ◽  
pp. 1-23 ◽  
Author(s):  
Kenneth Irving ◽  
Martina Kieninger ◽  
Oscar N. Ventura
Keyword(s):  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Enthalpies Of Formation ◽  
Isodesmic Reactions ◽  
Dft Methods ◽  
Functional Methods ◽  
The One ◽  
Isomeric Structures ◽  
Different Sources

The performance of a group of density functional methods of progressive complexity for the description of the ClO bond in a series of chlorine oxides was investigated. The simplest ClO radical species and the two isomeric structures XClO/ClOX for each X = H, Cl, and O were studied using the PW91, TPSS, B3LYP, PBE0, M06, M06-2X, BMK, and B2PLYP functionals. Geometry optimizations and reaction enthalpies and enthalpies of formation for each species were calculated using Pople basis sets and the (aug)-cc-pVnZ Dunning sets, with n = D, T, Q, 5, and 6. For the calculation of enthalpies of formation, atomization and isodesmic reactions were employed. Both the precision of the methods with respect to the increase of the basis sets, as well as their accuracy, were gauged by comparing the results with the more accurate CCSD(T) calculations, performed using the same basis sets as for the DFT methods. The results obtained employing composite chemical methods (G4, CBS-QB3, and W1BD) were also used for the comparisons, as well as the experimental results when they are available. The results obtained show that error compensation is the key for successful description of molecular properties (geometries and energies) by carefully selecting the method and basis sets. In general, expansion of the one-electron basis set to the limit of completeness does not improve results at the DFT level, but just the opposite. The enthalpies of formation calculated at the CCSD(T)/aug-cc-pV6Z for the species considered are generally in agreement with experimental determinations and the most accurate theoretical values. Different sources of error in the calculations are discussed in detail.

THEORETICAL STUDIES ON BOND DISSOCIATION ENERGIES FOR SOME THIOL COMPOUNDS BY DENSITRY FUNCTIONAL THEORY AND CBS-Q METHOD

2008 ◽  
Vol 07 (05) ◽  
pp. 943-951 ◽  
Author(s):  
XIAO-HONG LI ◽  
ZHENG-XIN TANG ◽  
ABRAHAM F. JALBOUT ◽  
XIAN-ZHOU ZHANG ◽  
XIN-LU CHENG
Keyword(s):  
Density Functional ◽  
Computational Cost ◽  
Basis Set ◽  
Basis Sets ◽  
Q Method ◽  
Bond Dissociation Energies ◽  
Functional Theory ◽  
Thiol Compounds ◽  
Bond Dissociation ◽  
Dissociation Energies

Quantum chemical calculations are used to estimate the bond dissociation energies (BDEs) for 15 thiol compounds. These compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86, PBE0) methods and the complete basis set (CBS-Q) method together with 6-311G** basis set. It is demonstrated that B3P86 and CBS-Q methods are accurate for computing the reliable BDEs for thiol compounds. In order to test whether the non-local BLYP method suggested by Fu et al.19 is general for our study and whether B3P86 method has a low basis set sensitivity, the BDEs for seven thiol compounds are also calculated using BLYP/6-31+G* and B3P86 method with 6-31+G*, 6-31+G**, and 6-311+G** basis sets for comparison. The obtained results are compared with the available experimental results. It is noted that B3P86 method is not sensitive to the basis set. Considering the inevitable computational cost of CBS-Q method and the reliability of the B3P86 calculations, B3P86 method with a moderate or a larger basis set may be more suitable to calculate the BDEs of the C–SH bond for thiol compounds.

Theoretical investigation of [Ru(tpy)2]2+, [Ru(tpy)(bpy)(H2O)]2+ and [Ru(tpy)(bpy)(Cl)]+ complexes in acetone revisited: Inclusion of strong spin–orbit couplings to quantum chemistry calculations

2016 ◽  
Vol 15 (01) ◽  
pp. 1650001
Author(s):  
Kenji Mishima ◽  
Takumi Kinoshita ◽  
Michitoshi Hayashi ◽  
Ryota Jono ◽  
Hiroshi Segawa ◽  
...  
Keyword(s):  
Experimental Data ◽  
Quantum Chemistry ◽  
Absorption Spectra ◽  
Density Functional ◽  
Order Perturbation ◽  
Basis Sets ◽  
Spin Orbit ◽  
First Order ◽  
Quantum Chemistry Calculations ◽  
First Order Perturbation

In the present paper, we theoretically reinvestigate structural properties, and photo-physical and chemical characteristics and electronic absorption spectra of three kinds of ruthenium polypyridyl complexes [Ru(tpy)[Formula: see text], [Ru(tpy)(bpy)(H2O)][Formula: see text], and [Ru(tpy)(bpy)(Cl)][Formula: see text] complexes in acetone (tpy[Formula: see text]2,2[Formula: see text],2[Formula: see text]-terpyridine and bpy[Formula: see text]2,2[Formula: see text]-bipyridine). In particular, the experimental absorption spectra of these complexes are revisited theoretically in detail and are simulated using the first-order perturbation theory based on time-dependent density functional theory (TD-DFT) where the first-order perturbation term is the spin–orbit (SO) coupling Hamiltonian, and quantum chemistry calculations based on various functionals and basis sets. It was found that in general the theory including SO coupling can reproduce experimental data better than the simple quantum chemistry calculation neglecting SO coupling, which indicates that SO coupling is very important to understand the optical features of these complexes and that therefore the mixing between singlet and triplet states is strong due to the large SO coupling constant of Ru atom involved in these complexes. This suggests the fact that the disagreement between the experimental and calculated absorption spectra was found in TDB3LYP/(SDD with triple-[Formula: see text] for Ru and 6-31G* for others) [Jakubikova EJ et al., Inorg Chem 48:10720, 2009] can be tracked down to the neglect of SO couplings. It was also found that the choice of the DFT functionals and basis sets is crucial for a good theoretical reproduction of experimental data.

Basis Set Effects in the Description of the Cl-O Bond in ClO and XClO Isomers (X=H,O,Cl) Using DFT and CCSD(T) Methods

2018 ◽  
Author(s):  
Oscar Ventura ◽  
Kenneth Irving ◽  
Martina Kieninger
Keyword(s):  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Enthalpies Of Formation ◽  
Isodesmic Reactions ◽  
Dft Methods ◽  
Functional Methods ◽  
The One ◽  
Isomeric Structures ◽  
Different Sources

<p>The performance of a group of density functional methods of progressive complexity for the description of the ClO bond in a series of chlorine oxides was investigated. The simplest ClO radical species as well as the two isomeric structures XClO/ClOX for each X=H, Cl and O were studied using the PW91, TPSS, B3LYP, PBE0, M06, M06-2X, BMK and B2PLYP functionals. Geometry optimizations as well as reaction enthalpies and enthalpies of formation for each species were calculated using Pople basis sets and the (aug)-cc-pVnZ Dunning sets, with n=2-6. For the calculation of enthalpies of formation, atomization as well as isodesmic reactions were employed. Both the precision of the methods with respect to the increase of the basis sets, as well as their accuracy, were gauged by comparing the results with the more accurate CCSD(T) calculations, performed using the same basis sets as for the DFT methods. The results obtained employing composite chemical methods (G4, CBS-QB3 and W1BD) were also used for the comparisons, as well as the experimental results when they are available. The results obtained show that error compensation is the key for successful description of molecular properties (geometries and energies) by carefully selecting method and basis sets. In general, expansion of the one-electron basis set to the limit of completeness does not improve results at the DFT level, but just the opposite. The enthalpies of formation calculated at the CCSD(T)/aug-cc-pV6Z for the species considered are generally in agreement with experimental determinations, and the most accurate derived theoretically up to present. Different sources of error in the calculations are discussed in detail.</p>

Molecular Structure, Vibrational Assignments and Nonlinear Optical Properties of Borazine by DFT Calculations

2021 ◽  
pp. 102-107
Author(s):  
Vinayak P. Deshmukh
Keyword(s):  
Molecular Structure ◽  
Finite Field ◽  
Density Functional ◽  
Nonlinear Optical ◽  
Field Method ◽  
Vibrational Frequencies ◽  
Basis Sets ◽  
Geometrical Parameters ◽  
Nlo Properties ◽  
Vibrational Assignments

In this work, density functional theory (DFT) combined with the finite field (FF) method has been adopted to study the molecular structure, vibrational assignments and nonlinear optical (NLO) properties of borazine. The geometrical parameters, vibrational frequencies and NLO properties have been obtained at B3LYP/6-311++G** level of theory. The optimized geometries and vibrational frequencies for borazine are in excellent agreement with the available experimental determinations. The B-N stretching mode observed is the most intense vibrational mode for borazine. The NLO properties of borazine have been investigated by using finite field method. The β and γ values are calculated at field strength of 0.006 a.u. for borazine using different methods and different basis sets.

Ab-initio HF and density functional theory investigations on the synthesis mechanism, conformational stability, molecular structure and UV spectrum of N’-Formylkynurenine

2016 ◽  
Vol 15 (01) ◽  
pp. 1650006 ◽  
Author(s):  
Nabil Omri ◽  
Mohammed Yahyaoui ◽  
Ridha Banani ◽  
Sabri Messaoudi ◽  
Fathi Moussa ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Stable Form ◽  
Static Properties ◽  
Uv Spectrum ◽  
Absorption Bands ◽  
Synthesis Mechanism ◽  
Stable Conformation

Tryptophan methyl ester (Trp-ME) degrades with singlet oxygen and produce compounds which are photosensitizers and may react to form other derivatives such as N’-Formylkynurénine (NFK) and kynurenine, which are the final products of this oxidation. In order to study and optimize the molecular structure of NFK and determine its different thermodynamic properties, we performed a conformational analysis by DFT/B3LYP method with 3-21G basis set. Six most stable conformations were observed through the analysis of the potential energy surfaces, obtained by a relaxed scan of the dihedral angles. The most stable form of NFK has been registered for D[Formula: see text], D[Formula: see text], D[Formula: see text], D[Formula: see text], D[Formula: see text], and D[Formula: see text]. The study was conducted by HF and DFT/B3LYP with 6-31G(d,p), 6-3[Formula: see text](d,p) and 6-31[Formula: see text](d,p) basis sets, on the optimized geometry of the most stable conformation and its thermodynamic and orbital properties. Two absorption bands were recorded at [Formula: see text][Formula: see text]nm and at [Formula: see text][Formula: see text]nm and were also determined by TD-DFT method. They showed good agreement with the UV experimental spectrum which confirms that it is a powerful tool to determine the dynamic and static properties of molecules. The surface of the electrostatic potential (ESP) of the NFK was also analyzed.

Molecular structure and tautomers of [30]trithia-2,3,5,10,12,13,15,20,22,23,25,30-dodecaazahexaphyrin

2013 ◽  
Vol 17 (03) ◽  
pp. 220-228 ◽  
Author(s):  
Yuriy A. Zhabanov ◽  
Alexander V. Zakharov ◽  
Sergei A. Shlykov ◽  
Olga N. Trukhina ◽  
Elena A. Danilova ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Density Functional Theory ◽  
Gas Phase ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Equilibrium Structure ◽  
Mass Spectrometric ◽  
Basis Sets ◽  
Functional Theory ◽  
Mass Spectrometric Experiment

The gas-phase molecular structure of the unsubstituted [30]trithia-2,3,5,10,12,13,15,20,22,23,25,30-dodecaazahexaphyrin (C30H15N15S3) has been studied by a synchronous gas electron diffraction and mass spectrometric experiment and density functional theory calculations using the B3LYP hybrid method and cc-pVTZ basis sets. The molecule has an equilibrium structure of D 3h symmetry with a planar macrocycle and the thiadiazole rings oriented in such a way that the sulfur atoms point outwards from the inner cavity. Tautomers of this compound have been studied by DFT computations.

Assessment of PBE0 Calculation of C-NO2 Bond Dissociation Energies for Nitroaromatic System

2014 ◽  
Vol 915-916 ◽  
pp. 675-678
Author(s):  
Xin Fang Su ◽  
Wei Huang ◽  
Hai Ying Wu
Keyword(s):  
Density Functional ◽  
Molecular System ◽  
Absolute Error ◽  
Basis Sets ◽  
Bond Dissociation Energies ◽  
Average Absolute Error ◽  
Functional Theory ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Experimental Values

Density functional theory (DFT) is used to calculate the C-NO2bond dissociation energies (BDEs) in nitrobenzene; 3-amino-nitrobenze; 4-amino-nitrobenze; 1,3-dinitrobenzene; 1,4-dinitrobenzene; 2-methyl-nitrobenzene; 4-methyl-nitrobenzene and 1,3,5-trinitrobenzene nitroaromatic molecular system. B3P86 and PBE0 methods in combination with 6-31G** and 6-311G** basis sets are employed. Comparison between the computational results and the experimental values reveals that the calculated C-NO2bond BDEs can be improved from B3P86 to PBE0 functional. Level of theory employing PBE0/6-311G** is found to be sufficiently reliable to compute BDEs of C-NO2bond for nitroaromatic molecules with an average absolute error of 0.98 kcal mol-1.

Theoretical enthalpies of formation and structural characterisation of halogenated nitromethanes and isomeric halomethyl nitrites

2012 ◽  
Vol 66 (12) ◽  
Author(s):  
Agnie Kosmas ◽  
Aristeidis Ntivas ◽  
Stavroula Liaska ◽  
Demetrios Papayannis
Keyword(s):  
Density Functional ◽  
Strong Dependence ◽  
Enthalpies Of Formation ◽  
Induction Effect ◽  
Functional Theory ◽  
Structural Characterisation ◽  
Dissociation Energies ◽  
Species Formation ◽  
Stable Species ◽  
Formation Enthalpies

AbstractThe structural, energetic, and thermochemical properties of a number of halogenated nitromethanes, CHnX3−n NO2, and the isomeric nitrites, CHnX3−n ONO, are investigated, using theoretical ab initio and density functional theory (DFT) electronic structure methods. Analysis of the results and comparison with the maternal species, nitromethane, CH3NO2, and methyl nitrite, CH3ONO, reveal strong dependence of the molecular properties on the halogen induction effect. Opposite trends are obtained in the C—N and C—O bond dissociation energies (BDE) upon halogenation and higher stabilities are calculated for the trans-nitrite isomers, in contrast with the plain alkyl families where the nitroalkanes are the most stable species. Formation enthalpies, ΔH fℴ, at 298 K are calculated for all halogenated isomers.

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