A computational study of the threshold energies of the 1,2-FCl interchange reaction of chlorofluoroethanes

2010 ◽  
Vol 88 (11) ◽  
pp. 1112-1117 ◽  
Author(s):  
William C. Everett ◽  
Bert E. Holmes ◽  
George L. Heard
Keyword(s):  
Carbon Atom ◽  
Thermodynamic Stability ◽  
Relative Stability ◽  
Activation Barrier ◽  
Computational Study ◽  
Basis Set ◽  
Fluorine Substitution ◽  
Interchange Reaction ◽  
Rearrangement Reaction ◽  
Threshold Energies

The 1,2-FCl rearrangement reaction of a series of haloethanes is investigated by comparisons of the optimized ground- and transition-state geometries. Investigation of the effect of level of theory and basis set shows that the trends in threshold energies for rearrangement are reproduced across all levels of theory and basis set, and hence that a moderate level of theory and basis set is adequate for investigating the important trends in this reaction. Threshold barriers increase when a large number of fluorine atoms are attached to the carbon atom bearing the interchanging fluorine, suggesting that the C–F bonds prove difficult to distort to the transition geometry; the increase is smaller for fluorine substitution on the carbon atom bearing the interchanging hydrogen atom. By considering sets of isomeric reactions, the barrier height is shown to closely follow the thermodynamic stability of the alkane undergoing rearrangement; however there is a secondary effect owing to the relative stability of the transition geometry. This relative stability can be related to the thermodynamic stability of a series of isomeric alkenes that resemble the transition geometry without the rearranging atoms. This series of molecules constitute an unusual set owing to the ability to consider these three contributions to the activation barrier separately.

scholarly journals Computational study of the threshold energy for the 1,2-interchange of X and R (X, R = halogens, pseudohalogens, and monovalent hydrocarbon groups) on CH2XCH2R

2016 ◽  
Vol 94 (12) ◽  
pp. 1038-1043 ◽  
Author(s):  
Ju-Sung Kim ◽  
Laura M. Brandt ◽  
George L. Heard ◽  
Bert E. Holmes
Keyword(s):  
Transition State ◽  
Ground State ◽  
Computational Study ◽  
Threshold Energy ◽  
Basis Set ◽  
Isomerization Reaction ◽  
Experimental Investigations ◽  
Carbon Backbone ◽  
Or Groups ◽  
Threshold Energies

Transition state geometries and threshold energies, E0, were computed for an unusual unimolecular isomerization reaction that exchanges two groups (X, R) on CH2XCH2R. An objective is to determine the most energetically feasible interchanges to guide experimental investigations. The interchanging species included halogens (F, Cl, Br) and pseudohalogens and monovalent hydrocarbons (H, SH, CH3, NH2, OH, OCF3, OCH3, CH=CH2, CH2CH3, CH2OH, C≡CH, CH2CF3, CCl3, CF3) attached to a two carbon backbone. Ground state and transition state geometries were optimized with the B3PW91 level of theory and 6-311+G(2d,p) basis set. The Br–Br interchange had the lowest E0 (141 kJ/mol), and CH3–H had the highest E0 (582 kJ/mol). In general, larger atoms or groups with lone pairs of electrons such as halogens, SH, OH, OCH3, OCF3, and NH2 tend to lower the E0 barrier for interchange, making them the most likely to be experimentally observed.

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.

scholarly journals Density Functional Theory and Complete Basis Set Ab Initio Computational Study of Five-, Six-, Seven- and Eight-hydrogen Coordinated Carbon Cations

1999 ◽  
Vol 23 (8) ◽  
pp. 502-503
Author(s):  
Branko S. Jursic
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Computational Study ◽  
Basis Set ◽  
Functional Theory ◽  
Complete Basis ◽  
Complete Basis Set ◽  
High Level

High level ab initio and density functional theory studies are performed on highly protonated methane species.

Reassessment of Acceptor Passivation Models in p-Type Hydrogenated GaAs

1989 ◽  
Vol 163 ◽  
Author(s):  
I. Szafranek ◽  
G.E. Stillman
Keyword(s):  
Hydrogen Bond ◽  
Coulomb Interaction ◽  
Strong Interaction ◽  
Thermodynamic Stability ◽  
Relative Stability ◽  
Present Model ◽  
Bohr Radius ◽  
Microscopic Models ◽  
P Type ◽  
Relative Thermodynamic Stability

AbstractThe existing microscopic models of acceptor passivation in p-type hydrogenated GaAs are reviewed in light of new experimental results concerning the relative thermodynamic stability of the passivating complexes. In particular, the present model for neutralization of Group II acceptors, Be, Mg and Zn, on Ga sites is shown to be inadequate to account for the observed trends, which imply existence of a strong interaction between the hydrogen and acceptor. It is proposed that a direct acceptor-hydrogen bond is formed due to attractive Coulomb interaction between the ionized species. The relative stability of the pair complex can be then explained based on electronegativity of the acceptor species. Passivation at intermediate pair separations up to about twice the Bohr radius of the nearest acceptor, is also discussed.

Computational study of polarizability anisotropies

2018 ◽  
Vol 96 (10) ◽  
pp. 934-938
Author(s):  
Delano P. Chong
Keyword(s):  
Small Molecules ◽  
Density Functional ◽  
Computational Study ◽  
Chem Phys ◽  
Basis Set ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Exchange Correlation Potential ◽  
Correlation Potential ◽  
Definition Of

The dipole polarizabilities (α) and polarizability anisotropies (Δα) of over 20 molecules are calculated to search for negative Δα. The geometry of each molecule is first optimized at the level of CCSD(T)/cc-pVQZ. Then, the α tensors are computed both with CCSD(T)/daug-cc-pVTZ in Gaussian 09 and with the exchange-correlation potential Vxc known as SAOP in the Amsterdam density functional theory program called ADF and a large basis set called QZ3P-3DIFFUSE. In addition to the popular formula of the ΔαRaman connected with Raman spectroscopy, we also present values of an alternative definition of the polarizability anisotropy ΔαKerr connected with Kerr spectroscopy, recently proposed by Kampfrath and colleagues (2018. Chem. Phys. Lett. 692: 319). On one hand, the signs of many ΔαRaman are undetermined; on the other hand, we obtain negative ΔαKerr for more than one-half of the small molecules studied. Of the 24 molecules studied, 18 have negative ΔαKerr.

scholarly journals Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study

2020 ◽  
Vol 10 (4) ◽  
pp. 1328 ◽  
Author(s):  
Hugo Gattuso ◽  
Barbara Fresch ◽  
Raphael D. Levine ◽  
Françoise Remacle
Keyword(s):  
Transient Absorption ◽  
Computational Study ◽  
Laser Pulses ◽  
Transient Absorption Spectroscopy ◽  
Basis Set ◽  
Charge Migration ◽  
Pump Probe ◽  
Electronic Response ◽  
Charge Transfer Excitons ◽  
Interdot Coupling

Interdot coherent excitonic dynamics in nanometric colloidal CdSe quantum dots (QD) dimers lead to interdot charge migration and energy transfer. We show by electronic quantum dynamical simulations that the interdot coherent response to ultrashort fs laser pulses can be characterized by pump-probe transient absorption spectroscopy in spite of the inevitable inherent size dispersion of colloidal QDs. The latter, leading to a broadening of the excitonic bands, induce accidental resonances that actually increase the efficiency of the interdot coupling. The optical electronic response is computed by solving the time-dependent Schrodinger equation including the interaction with the oscillating electric field of the pulses for an ensemble of dimers that differ by their size. The excitonic Hamiltonian of each dimer is parameterized by the QD size and interdot distance, using an effective mass approximation. Local and charge transfer excitons are included in the dimer basis set. By tailoring the QD size, the excitonic bands can be tuned to overlap and thus favor interdot coupling. Computed pump-probe transient absorption maps averaged over the ensemble show that the coherence of excitons in QD dimers that lead to interdot charge migration can survive size disorder and could be observed in fs pump-probe, four-wave mixing, or covariance spectroscopy.

scholarly journals Structure, electronic properties, NBO, NLO and chemi-cal reactivity of bis (1, 4-dithiafulvalene) derivatives: functional density theory study

2017 ◽  
Vol 6 (1) ◽  
pp. 18
Author(s):  
Tahar Abbaz ◽  
Amel Bendjeddou ◽  
Didier Villemin
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Computational Study ◽  
Molecular Geometry ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Reactivity Descriptors ◽  
Nlo Property ◽  
Functional Density Theory ◽  
Nucleophilic Reactivity

In this work, through computational study based on density functional theory (DFT/B3LYP) using basis set 6-31G (d,p) a number of global and local reactivity descriptors for a series of molecules containing a TTF function which are bis (1,4-dithiafulvalene) derivatives. They were computed to predict the reactivity and the reactive sites on the molecules. The molecular geometry and the electronic properties in the ground state such as frontier molecular orbital (HOMO and LUMO), ionization potential (I) and electron affinity (A) were investigated to get a better insight of the molecular properties. Molecular electrostatic potential (MEP) for all compounds were determined to check their electrophilic or nucleophilic reactivity. Fukui index, polarizability, hyperpolarizability, second order NLO property and natural bond orbital (NBO) analyses have also employed to determine the reactivity of bis (1,4-dithiafulvalene) derivatives.

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