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 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.

Optical properties of ideal γ-Al2O3 and with oxygen point defects: an ab initio study

RSC Advances ◽  
2015 ◽  
Vol 5 (68) ◽  
pp. 55088-55099 ◽  
Author(s):  
H. Papi ◽  
S. Jalali-Asadabadi ◽  
A. Nourmohammadi ◽  
Iftikhar Ahmad ◽  
J. Nematollahi ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Optical Properties ◽  
Ab Initio ◽  
Point Defects ◽  
Density Functional ◽  
Theory Approach ◽  
Ab Initio Study ◽  
Functional Theory ◽  
The Density Functional Theory

The optical properties of pure γ-Al2O3 and in the presence of oxygen point defects are investigated by the density functional theory approach using the PBE-GGA and TB-mBJ-GGA schemes.

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