COMPARATIVE QUANTUM STUDY ON TERT-BUTYL RADICAL AND CATION

2011 ◽  
Vol 10 (03) ◽  
pp. 325-348 ◽  
Author(s):  
ANNA IGNACZAK
Keyword(s):  
Density Functional ◽  
Structural Parameters ◽  
Coupling Constants ◽  
Basis Set ◽  
Basis Sets ◽  
Inversion Barrier ◽  
Gaussian Basis Sets ◽  
Dft Methods ◽  
Tert Butyl ◽  
Butyl Radical

Detailed comparative analysis of properties of the tert-butyl radical and cation is performed using 14 density functional (DFT) methods combined with double-zeta and triple-zeta quality Gaussian basis sets with polarization and diffuse functions. Stability of different conformers is discussed. Structural parameters, dipole moment, adiabatic ionization potential (IP), inversion barrier and isotropic hyperfine coupling constants are examined and compared to values obtained at the standard MP2 level and to experimental data available. All methods indicate that that the CC bond in the radical is longer than in the cation by about 0.033 Å. The IP values are found to be very sensitive to the method used and range from 612 to 709 kJ/mol, but majority oscillate around 646÷656 kJ/mol. Calculated inversion barrier for the radical is higher than the experimental estimate of 2.68 kJ/mol; with the 6-311++G** basis set and most DFT methods it is predicted in the range 3.86÷4.82 kJ/mol. All DFT methods predict for the out-of-plane CC3 bending mode of the radical the frequency around 260 cm-1, while in the cation the corresponding frequency is higher by about 180 cm-1.

Molecular orbital and 1H nuclear magnetic resonance studies of the inversion potentials of thianthrene and thioxanthene

1991 ◽  
Vol 69 (6) ◽  
pp. 927-933 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Christian Beaulieu
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Basis Set ◽  
Basis Sets ◽  
Inversion Barrier ◽  
H Nmr ◽  
Methylene Groups ◽  
Spin Spin Coupling ◽  
Split Valence

The inversion potentials, obtained from STO-3G, STO-3G(*), 3-21G, 3-21G(*), and 4-31G basis sets, are reported for thianthrene and thioxanthene, molecules in which both or only one of the methylene groups have been replaced by sulfur in 9,10-dihydroanthracene. Comparison with the available experimental data suggests that the split-valence bases lead to an overestimate, possibly by about 10 kJ/mol, of the inversion barrier in the crystal, whereas the STO-3G and STO-3G* basis sets underestimate this barrier. It appears that the inversion barrier for thianthrene is much lower in solution than in the crystal. The long-range coupling constants between the methylene and ring protons for thioxanthene in solution are consistent with an inversion barrier somewhat smaller than those obtained with the split-valence bases but rather larger than those predicted with the STO-3G basis set. The bond lengths and angles in the equilibrium structures of the two molecules, as computed with the 3-21G(*) basis, agree reasonably well with those in their crystals, except that the theoretical folding angles are smaller than measured. These discrepancies become less marked when expectation values are calculated from the theoretical inversion potentials at finite temperatures. Key words: MO calculations, inversion potentials of thianthrene and thioxanthene; 1H NMR, thioxanthene; spin–spin coupling constants, long range, in thioxanthene.

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.

scholarly journals Hyperfine Coupling Constants in Local Exact Two-Component Theory

2021 ◽  
Author(s):  
Yannick J. Franzke ◽  
Jason M. Yu
Keyword(s):  
Single Molecule ◽  
Density Functional ◽  
Hyperfine Coupling ◽  
Scalar Potential ◽  
Coupling Constants ◽  
Basis Set ◽  
Basis Sets ◽  
Spin Orbit ◽  
Finite Nucleus ◽  
Two Component

We present a highly efficient implementation of the electron-nucleus hyperfine coupling matrix within one-electron exact two-component (X2C) theory. The complete derivative of the X2C Hamiltonian is formed, i.e. the derivatives of the unitary decoupling transformation are considered. This requires solution of the response and Sylvester equations, consequently increasing the computational costs. Therefore, we apply the diagonal local approximation to the unitary decoupling transformation (DLU). The finite nucleus model is employed for both the scalar potential and the vector potential. Two-electron picture-change effects are modeled with the (modified) screened-nuclear spin--orbit approach. Our implementation is fully integral direct and OpenMP-parallelized. An extensive benchmark study regarding the Hamiltonian, the basis set, and the density functional approximation is carried out for a set of 12--17 transition-metal compounds. The error introduced by DLU is negligible and the DLU-X2C Hamiltonian accurately reproduces its four-component ``fully'' relativistic parent results. Functionals with a large amount of Hartree--Fock exchange such as CAM-QTP-02 and omega-B97X-D are generally favorable. The pure density functional r2SCAN performs remarkably and even outperforms the common hybrid functionals TPSSh and CAM-B3LYP. Fully uncontracted basis sets or contracted quadruple-zeta bases are required for accurate results. The capability of our implementation is demonstrated for [Pt(C6Cl5)4]- with more than 4700 primitive basis functions and four rare-earth single molecule magnets: [La(OAr*)3]-, [Lu(NR2)3]-, [Lu(OAr*)3]-, and [TbPc2]-. Here, the spin--orbit DLU-X2C Hamiltonian results in an excellent agreement with the experimental findings of all Pt, La, Lu, and Tb molecules.

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>

Application of numerical basis sets with a family of DFT methods to predict the transition states of Diels-Alder reactions: Assessing the accuracy through synchronous transit method

2017 ◽  
Author(s):  
Saurav Dutta ◽  
Bhabani S. Mallik
Keyword(s):  
Transition State ◽  
Alder Reaction ◽  
Diels Alder ◽  
Computational Method ◽  
Basis Set ◽  
Basis Sets ◽  
Gaussian Basis Sets ◽  
Dft Methods ◽  
Diels Alder Reaction ◽  
Transition State Search

<div> <table> <tr> <td> <p>Knowledge of the transition state is crucial in determining the mechanism in order to diversify the applicability of the reaction. The computational method is the most convenient way to locate the transition state in the absence any efficient experimental technique. We have applied the method of the transition state search on the Diels-Alder reaction computationally by means of combined linear synchronous transit and quadratic synchronous transit methods. Here we have shown that, of various methods adopted, BOP functional with numerical basis set provides a computationally economical alternative to the widely used B3LYP functional with higher Gaussian basis sets in the transition state search. It can reproduce the experimental parameters like activation energy of the Diels-Alder reaction, and the calculations are much faster than the corresponding other functional based calculations.</p> </td> </tr> </table> </div>

Application of numerical basis sets with a family of DFT methods to predict the transition states of Diels-Alder reactions: Assessing the accuracy through synchronous transit method

2017 ◽  
Author(s):  
Saurav Dutta ◽  
Bhabani S. Mallik
Keyword(s):  
Transition State ◽  
Alder Reaction ◽  
Diels Alder ◽  
Computational Method ◽  
Basis Set ◽  
Basis Sets ◽  
Gaussian Basis Sets ◽  
Dft Methods ◽  
Diels Alder Reaction ◽  
Transition State Search

<div> <table> <tr> <td> <p>Knowledge of the transition state is crucial in determining the mechanism in order to diversify the applicability of the reaction. The computational method is the most convenient way to locate the transition state in the absence any efficient experimental technique. We have applied the method of the transition state search on the Diels-Alder reaction computationally by means of combined linear synchronous transit and quadratic synchronous transit methods. Here we have shown that, of various methods adopted, BOP functional with numerical basis set provides a computationally economical alternative to the widely used B3LYP functional with higher Gaussian basis sets in the transition state search. It can reproduce the experimental parameters like activation energy of the Diels-Alder reaction, and the calculations are much faster than the corresponding other functional based calculations.</p> </td> </tr> </table> </div>

A DFT INVESTIGATION ON BASIS SET SIZE AND HYDROGEN-BONDING EFFECTS ON 17O AND 2H NQR PARAMETERS

2013 ◽  
Vol 12 (04) ◽  
pp. 1350022 ◽  
Author(s):  
MEHDI D. ESRAFILI ◽  
NAFISEH MOHAMMADIRAD
Keyword(s):  
Density Functional ◽  
Quadrupole Coupling Constant ◽  
Basis Set ◽  
Basis Sets ◽  
Coupling Constant ◽  
Dft Methods ◽  
Functional Theory ◽  
Set Size ◽  
Quadrupole Coupling ◽  
Consistent Basis

A systematic theoretical study on various maleic acid (MA) clusters has been carried out employing density functional theory (DFT) methods. The performance of two different functionals namely B3LYP and M06 in the prediction of geometries, 17 O and 2 H nuclei quadrupole coupling constant (CQ) values of the MA clusters has been assessed comparing the results to those experimental data. For DFT calculations, several basis sets have been used, including the recently developed Jensen's polarization-consistent basis set families, pcJ-n and pcS-n (n = 0,1,2,3). Calculations at the basis set limit indicate that the value of CQ(2 H ) in monomer MA, changes by 0.01–0.04 kHz for each of the final two basis set increments, and seems reasonable to conclusion that the pcJ-3 result is within a few kHz of the basis set limit. Convergence with respect to basis set size was found to be very good, and the pcJ-1 and pcS-1 basis sets provided a good compromise between the basis set limit and computational expense. In most cases, the differences between B3LYP and M06 results for a given basis set are in a range of 1–2%. On the other hand, no systematic changes in the CQ(17 O ) or CQ(2 H ) were found for basis sets larger than double-ζ. Thus, the usual assumption that double-ζ basis set (pcJ-1 and pcS-1) results in the acceptable CQ values, seems to be valid in the case of 17 O and 2 H nuclei.

scholarly journals Factors Governing the Chemical Stability and NMR Parameters of Uracil Tautomers and Its 5-Halogen Derivatives

Molecules ◽  
2020 ◽  
Vol 25 (17) ◽  
pp. 3931 ◽  
Author(s):  
Kacper Rzepiela ◽  
Aneta Buczek ◽  
Teobald Kupka ◽  
Małgorzata A. Broda
Keyword(s):  
Electrostatic Interactions ◽  
Density Functional ◽  
Chemical Shifts ◽  
Polarizable Continuum Model ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Basis Set ◽  
Basis Sets ◽  
Nmr Parameters ◽  
Solvent Model

We report on the density functional theory (DFT) modelling of structural, energetic and NMR parameters of uracil and its derivatives (5-halogenouracil (5XU), X = F, Cl, Br and I) in vacuum and in water using the polarizable continuum model (PCM) and the solvent model density (SMD) approach. On the basis of the obtained results, we conclude that the intramolecular electrostatic interactions are the main factors governing the stability of the six tautomeric forms of uracil and 5XU. Two indices of aromaticity, the harmonic oscillator model of aromaticity (HOMA), satisfying the geometric criterion, and the nuclear independent chemical shift (NICS), were applied to evaluate the aromaticity of uracil and its derivatives in the gas phase and water. The values of these parameters showed that the most stable tautomer is the least aromatic. A good performance of newly designed xOPBE density functional in combination with both large aug-cc-pVQZ and small STO(1M)−3G basis sets for predicting chemical shifts of uracil and 5-fluorouracil in vacuum and water was observed. As a practical alternative for calculating the chemical shifts of challenging heterocyclic compounds, we also propose B3LYP calculations with small STO(1M)−3G basis set. The indirect spin–spin coupling constants predicted by B3LYP/aug-cc-pVQZ(mixed) method reproduce the experimental data for uracil and 5-fluorouracil well.

scholarly journals A Density-Based Basis-Set Correction for Wave Function Theory

2019 ◽  
Author(s):  
Pierre-Francois Loos ◽  
Barthelemy Pradines ◽  
Anthony Scemama ◽  
Julien Toulouse ◽  
Emmanuel Giner
Keyword(s):  
Density Functional ◽  
Ad Hoc ◽  
Basis Set ◽  
Basis Sets ◽  
Separation Function ◽  
Gaussian Basis Sets ◽  
Functional Theory ◽  
Separation Parameter ◽  
Range Correlation ◽  
Complete Basis Set

<div><div><div><p>We report a universal density-based basis-set incom-<br>pleteness correction that can be applied to any wave<br>function method. The present correction, which ap-<br>propriately vanishes in the complete basis set (CBS)<br>limit, relies on short-range correlation density func-<br>tionals (with multi-determinant reference) from range-<br>separated density-functional theory (RS-DFT) to esti-<br>mate the basis-set incompleteness error. Contrary to<br>conventional RS-DFT schemes which require an ad hoc<br>range-separation parameter μ, the key ingredient here<br>is a range-separation function μ(r) that automatically<br>adapts to the spatial non-homogeneity of the basis-set<br>incompleteness error. As illustrative examples, we show how this density-based correction allows us to obtain CCSD(T) atomization and correlation energies near the CBS limit for the G2 set of molecules with compact Gaussian basis sets.</p></div></div></div>

scholarly journals A Density-Based Basis-Set Correction for Wave Function Theory

2019 ◽  
Author(s):  
Pierre-Francois Loos ◽  
Barthelemy Pradines ◽  
Anthony Scemama ◽  
Julien Toulouse ◽  
Emmanuel Giner
Keyword(s):  
Density Functional ◽  
Ad Hoc ◽  
Basis Set ◽  
Basis Sets ◽  
Separation Function ◽  
Gaussian Basis Sets ◽  
Functional Theory ◽  
Separation Parameter ◽  
Range Correlation ◽  
Complete Basis Set

<div><div><div><p>We report a universal density-based basis-set incom-<br>pleteness correction that can be applied to any wave<br>function method. The present correction, which ap-<br>propriately vanishes in the complete basis set (CBS)<br>limit, relies on short-range correlation density func-<br>tionals (with multi-determinant reference) from range-<br>separated density-functional theory (RS-DFT) to esti-<br>mate the basis-set incompleteness error. Contrary to<br>conventional RS-DFT schemes which require an ad hoc<br>range-separation parameter μ, the key ingredient here<br>is a range-separation function μ(r) that automatically<br>adapts to the spatial non-homogeneity of the basis-set<br>incompleteness error. As illustrative examples, we show how this density-based correction allows us to obtain CCSD(T) atomization and correlation energies near the CBS limit for the G2 set of molecules with compact Gaussian basis sets.</p></div></div></div>

Sign in / Sign up

Export Citation Format

Share Document