Asymmetrically distorted structures of monosilacyclobutane and disilacyclobutane radical cations studied by ab initio and density functional theories

2012 ◽  
Vol 90 (7) ◽  
pp. 584-596
Author(s):  
Z.J. Cai ◽  
Y.J. Shi
Keyword(s):  
Ab Initio ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Strong Support ◽  
Electronic States ◽  
Radical Cations ◽  
Ring Structure ◽  
The Other ◽  
Significant Difference ◽  
Ring Structures

The geometrical and electronic structures of a series of six monosilacyclobutane and 1,3-disilacyclobutane radical cations were systematically studied using ab initio and density functional theories. It was shown that all six radical cations possess an asymmetrically distorted structure in their ground electronic states. In the asymmetrically distorted C1 structure of monosilacyclobutane cations, one Si–C bond was elongated and the other was shortened. For the disilacyclobutane cations, two ring bonds were elongated and the other two contracted. The asymmetrical distortion was enhanced by exocyclic methyl substitutions and weakened by endocyclic Si substitution. The unpaired electron was localized mainly in the elongated σ(Si–C) ring bond(s) in all six cations. Studies of the excited electronic states of the cations provided strong support that the asymmetrical distortion in the four-membered-ring cations originates from the second-order Jahn–Teller effect. It was found that the puckered ring structures in the monosilacyclobutane molecules were maintained upon ionization, whereas 1,3-disilacyclobutane cations changed to a planar ring structure. Examination of the potential energy surfaces of all six cations showed that the Si–C ring bond elongation is the main contributor to the significant difference in the geometry change between monosilacyclobutane and disilacyclobutane species upon ionization.

A Combined ab initio and Density Functional Study of the Electronic Structure of Thymine and 2-Thiothymine Radicals

2003 ◽  
Vol 68 (12) ◽  
pp. 2322-2334 ◽  
Author(s):  
Robert Vianello ◽  
Zvonimir B. Maksić
Keyword(s):  
Ab Initio ◽  
Spin Density ◽  
Density Functional ◽  
Radical Cations ◽  
Functional Study ◽  
Theory Approach ◽  
Functional Theory ◽  
Adiabatic Ionization Potential ◽  
Highest Occupied Molecular Orbital ◽  
Positively Charged

The electronic and energetic properties of thymine (1) and 2-thiothymine (2) and their neutral and positively charged radicals are considered by a combined ab initio and density functional theory approach. It is conclusively shown that ionization of 1 and 2 greatly facilitates deprotonation of the formed radical cations thus making the proton transfer between charged and neutral precursor species thermodynamically favourable. The adiabatic ionization potential of 1 and 2 are analysed. It appears that ADIP(1) is larger than ADIP(2) by 10 kcal/mol, because of greater stability of the highest occupied molecular orbital (HOMO) of the former. It is also shown beyond any doubt that the spin density in neutral and cationic radical of 2 is almost exclusively placed on the σ-3p AO of sulfur implying that these two systems represent rather rare sigma-radicals. In contrast, the spin density of radicals of 1 is distributed over their π-network.

scholarly journals Electrochemical and Spectroelectrochemical Studies on the Reactivity of Perimidine–Carbazole–Thiophene Monomers towards the Formation of Multidimensional Macromolecules versus Stable π-Dimeric States

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2167
Author(s):  
Malgorzata Czichy ◽  
Patryk Janasik ◽  
Pawel Wagner ◽  
David L. Officer ◽  
Mieczyslaw Lapkowski
Keyword(s):  
Conjugated Polymer ◽  
Density Functional ◽  
Radical Cations ◽  
Covalent Bonding ◽  
Oxidation States ◽  
Solid Product ◽  
Functional Theory ◽  
Subsequent Oxidation ◽  
Molecular Ordering ◽  
Significant Difference

During research on cross-linked conducting polymers, double-functionalized monomers were synthesized. Two subunits potentially able to undergo oxidative coupling were used—perimidine and, respectively, carbazole, 3,6-di(hexylthiophene)carbazole or 3,6-di(decyloxythiophene)carbazole; alkyl and alkoxy chains as groups supporting molecular ordering and 14H-benzo[4,5]isoquinone[2,1-a]perimidin-14-one segment promoting CH⋯O interactions and π–π stacking. Electrochemical, spectroelectrochemical, and density functional theory (DFT) studies have shown that potential-controlled oxidation enables polarization of a specific monomer subunit, thus allowing for simultaneous coupling via perimidine and/or carbazole, but mainly leading to dimer formation. The reason for this was the considerable stability of the dicationic and tetracationic π-dimers over covalent bonding. In the case of perimidine-3,6-di(hexylthiophene)carbazole, the polymer was not obtained due to the steric hindrance of the alkyl substituents preventing the coupling of the monomer radical cations. The only linear π-conjugated polymer was obtained through di(decyloxythiophene)carbazole segment from perimidine-di(decyloxythiophene)-carbazole precursor. Due to the significant difference in potentials between subsequent oxidation states of monomer, it was impossible to polarize the entire molecule, so that both directions of coupling could be equally favored. Subsequent oxidation of this polymer to polarize the side perimidine groups did not allow further crosslinking, because rather the π–π interactions between these perimidine segments dominate in the solid product.

Boron Segregation on the ${\rm Si}(111)\sqrt{3} \times \sqrt{3}{\rm R}30^\circ$ Surface

2003 ◽  
Vol 10 (02n03) ◽  
pp. 201-205 ◽  
Author(s):  
Hongqing Shi ◽  
M. W. Radny ◽  
P. V. Smith
Keyword(s):  
Plane Wave ◽  
Ab Initio ◽  
Density Functional ◽  
Strong Support ◽  
Am1 Calculations ◽  
Segregation Energy ◽  
Additional Information ◽  
Boron Segregation ◽  
Cluster Calculations ◽  
Functional Code

In this paper we report the results of calculations of the energies associated with the segregation of boron on the [Formula: see text] surface. These calculations have been carried out using the plane wave pseudopotential density functional code fhi98md in a periodic slab formalism. The segregation energy is predicted to be -0.77 eV. This prediction is intermediate between the "experimentally determined" values of -0.33 eV and -0.48 eV, and the values of -1.83 eV and -2.10 eV determined from AM1 cluster calculations. Additional information has been obtained by performing ab initio density functional cluster calculations using the Gaussian98 code. These latter results indicate that the AM1 calculations significantly overestimate the segregation energy of boron on the [Formula: see text] surface. They also provide strong support for the fhi98md calculations.

Density functional theory study on the structural, reactivity, and electronic properties of all mono-, di-, tri-, tetra-, and penta-fluoroanilines as monomers for conducting polymers

2012 ◽  
Vol 90 (10) ◽  
pp. 902-914 ◽  
Author(s):  
Hossein Shirani Il Beigi
Keyword(s):  
Density Functional Theory ◽  
Conducting Polymers ◽  
Structural Properties ◽  
Density Functional ◽  
Dipole Moments ◽  
Radical Cations ◽  
The Other ◽  
Functional Theory ◽  
Density Distributions ◽  
Electric Polarizabilities

Electrical and structural properties of mono-, di-, tri-, tetra-, and penta-fluoroanilines as candidate monomers for new conducting polymers have been investigated using hybrid density functional theory (B3LYP/6–311+G**) based methods. The effects of the number and position of the fluorine atoms on the electrical and structural properties of fluoroanilines and their radical cations have also been investigated. The values of the vibrational frequencies, charge and spin-density distributions, ionization potentials, dipole moments, electric polarizabilities, HOMO-LUMO gaps, and the NICS values of these compounds have been calculated and analyzed as well. The results showed that the double bonds in 2-fluoroaniline and 2,5-difluoroaniline are more delocalized compared with other fluoroanilines; therefore, these molecules have the most aptitude for the electropolymerization reactions. The frequency analysis showed that the electrochemical stability of 2-fluoroaniline is greater than the other fluoroanilines. Also, this molecule possesses the largest NICS value compared to the other fluoroanilines. Consequently, 2-fluoroaniline has the largest ring current and the highest conductivity among all other monomers. Based on the results obtained, 2-fluoroaniline and 2,5-difluoroaniline are the best candidate monomers among all fluoroanilines for the synthesis of corresponding conducting polymers.

Coupled ab initio potential energy surfaces for the two lowest 2A′ electronic states of the C2H molecule

2000 ◽  
Vol 98 (23) ◽  
pp. 1925-1938 ◽  
Author(s):  
M. BOGGIO-PASQUA ◽  
A. I. VORONIN ◽  
PH. HALVICK ◽  
J.-C. RAYEZ ◽  
A. J. C. VARANDAS
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Potential Energy Surfaces ◽  
Electronic States ◽  
Energy Surfaces

scholarly journals DFT and ab initio calculations of ionization potentials, proton affinities and bond dissociation enthalpies of aromatic compounds

2019 ◽  
Vol 12 (2) ◽  
pp. 225-240
Author(s):  
Denisa Cagardová ◽  
Martin Michalík ◽  
Erik Klein ◽  
Vladimír Lukeš ◽  
Zoran Marković
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Radical Scavenging ◽  
Radical Cations ◽  
Ionization Potentials ◽  
Phase Reaction ◽  
Proton Affinities ◽  
Functional Theory ◽  
Bond Dissociation ◽  
Nitro Derivatives

Abstract Theoretical study of phenol, thiophenol, benzeneselenol, aniline and their para-amino and paranitro derivatives is presented. Neutral molecules, their deprotonated forms, neutral radicals, and radical cations were studied using three Density Functional Theory (DFT) functionals as well as combined DFT and ab initio G4 method in order to calculate the N—H, O—H, S—H, and Se—H bond dissociation enthalpies (BDE), proton affinities of corresponding anions (PA) and ionization potentials (IP) of studied compounds. These quantities represent fundamental reaction enthalpies related to the radical scavenging action of primary antioxidants. Calculated values were compared with available experimental data to assess applicability of the computational approaches employed. M06-2X/6-311++G(d,p) and G4 methods showed the best agreement with the available experimental gas-phase reaction enthalpies.

Prediction of the photoelectron spectrum for XPY2 (X = H, F, Cl; Y = O, S) type of molecules by ab initio and DFT methods

2006 ◽  
Vol 84 (1) ◽  
pp. 5-9 ◽  
Author(s):  
Didier Bégué ◽  
Jean-marc Sotiropoulos ◽  
Claude Pouchan ◽  
Daisy Y Zhang
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Radical Cations ◽  
Dft Methods ◽  
Functional Theory ◽  
Hartree Fock ◽  
Orbital Energies ◽  
Koopmans Theorem ◽  
Vertical Ionization Potentials ◽  
Hybrid Density Functional

The present study reports the theoretical vertical ionization potentials (IPs) for all the valence electrons in six XPY2 molecules by utilizing the corrected orbital energies calculated with three theoretical methods, namely, the ab initio Hartree–Fock (HF), and both the pure and hybrid density functional theory (DFT) methods at, respectively, the BLYP/6-311+G* and B3lYP/6-311+G* levels of theory. Evaluation of the numerical corrections to the orbital energies was achieved by comparisons with the IP values obtained via explicit computation of the energy differences between the neutral molecules and the corresponding radical cations (the ΔSCF method) and shows values from –0.9 to –1.9 eV for the HF, and positive values from 2.9 to 3.9 eV and from 1.8 to 2.4 eV for the pure and hybrid DFT methods, respectively. In contrast to the orbital energies, the ΔSCF method is shown to give consistent values among the three methods, as well as reasonable agreement with the experimental IP values.Key words: ionization potential, phosphorane, Koopmans' theorem, Janak's theorem.

Sign in / Sign up

Export Citation Format

Share Document