Ab Initio Study of Clean and Hydrogen-Saturated Unreconstructed SiC{0001} Surfaces

Using density functional theory, we investigate the 6H-SiC{0001} surfaces in the unreconstructed 1 × 1 and the H-passivated configuration. The strong correlation effects of the dangling bonds at the surface are treated by spin-polarised calculations including the Hubbard-U parameter. We find that the clean surfaces are semiconducting with surface states in good agreement with experimental data. The impact of the Hubbard-U is stronger on the C-terminated face. For the H-passivated surfaces we find resonances in the valence band. The antibonding C−H state is located in the upper part of the bandgap around the ¯􀀀-point.

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STRUCTURAL AND ELECTRONIC PROPERTIES OF BRIDGED BITHIOPHENE S-OXIDES (BTO) WITH S, S=O, O, SiH2 and BH2 BRIDGE: SEMI-EMPIRICAL AND AB INITIO STUDY

Southern Brazilian Journal of Chemistry - Southern Brazilian Journal of Chemistry, Volume 28, No. 28, 2020 ◽

10.48141/sbjchem.v18.n18.2010.6_2010.pdf ◽

2010 ◽

Vol 18 (18) ◽

pp. 1-10

Author(s):

Banjo Semire ◽

Isaiah Ajibade Adejoro ◽

Olusegun Ayobami Odunola

Keyword(s):

Density Functional Theory ◽

Thermodynamic Properties ◽

Ab Initio ◽

Density Functional ◽

Ab Initio Study ◽

Empirical Methods ◽

Functional Theory ◽

Structural And Electronic Properties ◽

Semi Empirical ◽

Good Agreement

In this paper, we theoretically studied the geometries, stabilities, electronic and thermodynamic properties of bridged bithiophene S-oxide (BTO-X) derivates (with X = BH2, SiH2, S, S=O, and O) by using semi-empirical methods, ab-initio, and Density functional theory. The geometries and thermodynamic parameters calculated by PM3 were in good agreement with that of B3LYP/6-31G(d). The bandgap calculated by B3LYP/6-31G(d) ranged from 3.94eV (BTO-O)-3.16eV (BTO-BH2). The absorption λmax calculated suing B3LYP/6-31G(d) shifted to longer wavelength with X=BH2, SiH2, and S=O due to enhancement of π-conjugated system whereas, BTO-S and BTO-O shifted to shorter wavelengths as compared to dimmer thiophene S-oxide (2TO).

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A computational study of the fluctional behaviour of group 14 substituted ortho-semiquinone radicals

Canadian Journal of Chemistry ◽

10.1139/v10-082 ◽

2011 ◽

Vol 89 (2) ◽

pp. 235-240 ◽

Cited By ~ 1

Author(s):

K. U. Ingold ◽

Gino A. DiLabio

Keyword(s):

Experimental Data ◽

Density Functional Theory ◽

Rate Constant ◽

Density Functional ◽

Computational Study ◽

Group 14 ◽

Functional Theory ◽

Semiquinone Radicals ◽

Experimental Values ◽

Good Agreement

The dynamics of the 1,4-migration of some O-substituted 3,5-di-tert-butyl-ortho-semiquinone radicals have been calculated by density-functional theory (DFT). There is very good agreement in the rate constant and Arrhenius parameters between these calculations and experimental values for migration of H, D, and the Me3Si group. For the Me3Sn group, the calculations indicate an incredibly fast migration (k293K = 2.0 × 1012 s–1), a result that is consistent with experimental data (k293K > 109 s–1). Other O-substituents examined by DFT and compared with experimental data were H3C and Me2ClSn.

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Electronic structure and spectroscopy of homoleptic compounds of dimolybdenum using TDDFT

Canadian Journal of Chemistry ◽

10.1139/cjc-2015-0210 ◽

2016 ◽

Vol 94 (1) ◽

pp. 20-27

Author(s):

Pere Vilarrubias

Keyword(s):

Experimental Data ◽

Density Functional Theory ◽

Electronic Structure ◽

Density Functional ◽

Molecular Orbitals ◽

Time Dependent ◽

Electronic Transitions ◽

Functional Theory ◽

Dependent Density ◽

Good Agreement

Ten compounds of dimolybdenum are studied using density functional theory and time-dependent density functional theory. The energy of the strongest symmetry-allowed bands is calculated. The results are then compared with experimental data, when available. The PW91 functional gives results for geometry and for the energy of the δ→δ* band that show good agreement with experimental data. However, the B3LYP functional gives more realistic values for the whole spectrum when the results are compared with experimental data. Finally, the different values of energy of these bands are explained analyzing the molecular orbitals involved in these transitions. Some ligands can act as an unsaturated system in conjugation with the delta bond, modifying the energies of the electronic transitions.

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Density functional theory (DFT) and Hartree–Fock (HF) calculations of potential p–vinylbenzyl chloride-based macroinitiator for atom transfer radical polymerization

Canadian Journal of Physics ◽

10.1139/cjp-2015-0665 ◽

2016 ◽

Vol 94 (3) ◽

pp. 290-304 ◽

Cited By ~ 4

Author(s):

Feride Akman

Keyword(s):

Experimental Data ◽

Density Functional Theory ◽

Potential Energy ◽

Density Functional ◽

Energy Surface ◽

Functional Theory ◽

Hartree Fock ◽

Experimental Values ◽

Good Agreement ◽

Hf Calculations

The spectroscopic properties of poly (styrene–co–p–vinylbenzyl chloride) (poly (St-co-VBC)) were investigated by Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopic techniques. The molecular geometry and vibrational frequencies of macroinitiator, poly (St-co-VBC), were calculated by using density functional theory (DFT) and Hartree–Fock (HF) methods with 6–31 G+ (d, p) as a basis set. Calculated theoretical values are shown to be in good agreement with that of experimental values. An excellent harmony between the two data sets was verified. Besides, the experimental data of macroinitiator were compared with experimental data of its corresponding monomers such as St and VBC. The dimer and trimer forms of macroinitiator are used as significant contributions for getting an accurate interpretation of the experimental frequencies of poly (St-co-VBC). The results revealed that the change from St and VBC to poly (St-co-VBC) should be characterized by the disappearance of the CH2=CH bonds of the vinyl group and the appearance of the aliphatic C–H and CH2 bonds. The geometrical parameters, Mulliken atomic charges and frontier molecular orbitals energies were also calculated using the same theoretical methods. The chemical shifts were calculated by using the gauge–including atomic orbital method and all the theoretically predicted values were shown to be in good agreement with experimental values. Molecular orbital properties, molecular electrostatic potential, and the potential energy surface for the atom transfer radical polymerization (ATRP) of the macroinitiator were studied with DFT and HF calculations. The potential energy surface of the ATRP initiator is decided by their electronic effect and steric hindrance effect simultaneously.

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Theoretical study of the adsorption of benzene on coinage metals

Beilstein Journal of Organic Chemistry ◽

10.3762/bjoc.10.185 ◽

2014 ◽

Vol 10 ◽

pp. 1775-1784 ◽

Cited By ~ 40

Author(s):

Werner Reckien ◽

Melanie Eggers ◽

Thomas Bredow

Keyword(s):

Experimental Data ◽

Density Functional Theory ◽

Density Functional ◽

Theoretical Study ◽

Dispersion Correction ◽

Functional Theory ◽

Coinage Metals ◽

Adsorption Energies ◽

Theoretical Results ◽

Good Agreement

The adsorption of benzene on the M(111), M(100) and M(110) surfaces of the coinage metals copper (M = Cu), silver (M = Ag) and gold (M = Au) is studied on the basis of density functional theory (DFT) calculations with an empirical dispersion correction (D3). Variants of the Perdew–Burke–Ernzerhof functionals (PBE, RPBE and RevPBE) in combination with different versions of the dispersion correction (D3 and D3(BJ)) are compared. PBE-D3, PBE-D3(BJ) and RPBE-D3 give similar results which exhibit a good agreement with experimental data. RevPBE-D3 and RevPBE-D3(BJ) tend to overestimate adsorption energies. The inclusion of three-center terms (PBE-D3(ABC)) leads to a slightly better agreement with the experiment in most cases. Vertical adsorbate–substrate distances are calculated and compared to previous theoretical results. The observed trends for the surfaces and metals are consistent with the calculated adsorption energies.

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What correlation effects are covered by density functional theory?

Molecular Physics ◽

10.1080/002689700424440 ◽

2000 ◽

Vol 98 (20) ◽

pp. 1639-1658 ◽

Cited By ~ 5

Author(s):

Yuan He, Jurgen Grafenstein, Elfi Kraka,

Keyword(s):

Density Functional Theory ◽

Density Functional ◽

Correlation Effects ◽

Functional Theory

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An Evaluation of the Impact of the Amount of Potassium Hydroxide on the Porous Structure Development of Activated Carbons

Materials ◽

10.3390/ma14082045 ◽

2021 ◽

Vol 14 (8) ◽

pp. 2045

Author(s):

Mirosław Kwiatkowski ◽

Elżbieta Broniek ◽

Vanessa Fierro ◽

Alain Celzard

Keyword(s):

Density Functional Theory ◽

Porous Structure ◽

Potassium Hydroxide ◽

Density Functional ◽

Activated Carbons ◽

Chemical Activation ◽

Appropriate Technology ◽

Functional Theory ◽

Homogeneous Surface ◽

The Impact

This paper presents the results of an evaluation of the impact of the amount of potassium hydroxide on the obtained porous structure of the activated carbons derived from the shells of pistachios, hazelnuts, and pecans by carbonization and subsequent chemical activation with potassium hydroxide by different adsorption methods: Brunauer–Emmett–Teller, Dubinin–Raduskevich, the new numerical clustering-based adsorption analysis, Quenched Solid Density Functional Theory, and 2D-Non-linear Density Functional Theory for Heterogeneous Surfaces, applied to nitrogen adsorption isotherms at −196 °C. Based on the conducted research, a significant potential for the production of activated carbons from waste materials, such as nut shells, has been demonstrated. All the activated carbons obtained in the present study at the activator/char mass ratio R = 4 exhibited the most developed porous structure, and thus very good adsorption properties. However, activated carbons obtained from pecan shells deserve special attention, as they were characterized by the most homogeneous surface among all the samples analyzed, i.e., by a very desirable feature in most adsorption processes. The paper demonstrates the necessity of using different methods to analyze the porous structure of activated carbons in order to obtain a complete picture of the studied texture. This is because only a full spectrum of information allows for correctly selecting the appropriate technology and conditions for the production of activated carbons dedicated to specific industrial applications. As shown in this work, relying only on the simplest methods of adsorption isotherm analysis can lead to erroneous conclusions due to lack of complete information on the analyzed porous structure. This work thus also explains how and why the usual characterizations of the porous structure of activated carbons derived from lignocellulosic biomass should not be taken at face value. On the contrary, it is advisable to cross reference several models to get a precise idea of the adsorbent properties of these materials, and therefore to propose the most suitable production technology, as well as the conditions of the preparation process.

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A DFT study of spherands containing five anisyl groups — Highly preorganized to bind the alkali metal

Canadian Journal of Chemistry ◽

10.1139/v06-130 ◽

2006 ◽

Vol 84 (8) ◽

pp. 1045-1049 ◽

Cited By ~ 4

Author(s):

Shabaan AK Elroby ◽

Kyu Hwan Lee ◽

Seung Joo Cho ◽

Alan Hinchliffe

Keyword(s):

Density Functional Theory ◽

Binding Energy ◽

Density Functional ◽

Ionic Radius ◽

Binding Energies ◽

Cavity Size ◽

X Ray Diffraction ◽

Functional Theory ◽

X Ray ◽

Good Agreement

Although anisyl units are basically poor ligands for metal ions, the rigid placements of their oxygens during synthesis rather than during complexation are undoubtedly responsible for the enhanced binding and selectivity of the spherand. We used standard B3LYP/6-31G** (5d) density functional theory (DFT) to investigate the complexation between spherands containing five anisyl groups, with CH2–O–CH2 (2) and CH2–S–CH2 (3) units in an 18-membered macrocyclic ring, and the cationic guests (Li+, Na+, and K+). Our geometric structure results for spherands 1, 2, and 3 are in good agreement with the previously reported X-ray diffraction data. The absolute values of the binding energy of all the spherands are inversely proportional to the ionic radius of the guests. The results, taken as a whole, show that replacement of one anisyl group by CH2–O–CH2 (2) and CH2–S–CH2 (3) makes the cavity bigger and less preorganized. In addition, both the binding and specificity decrease for small ions. The spherands 2 and 3 appear beautifully preorganized to bind all guests, so it is not surprising that their binding energies are close to the parent spherand 1. Interestingly, there is a clear linear relation between the radius of the cavity and the binding energy (R2 = 0.999).Key words: spherands, preorganization, density functional theory, binding energy, cavity size.

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