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Ab-Initio calculations of the CO adsorption and dissociation on substitutional Fe-Cu surface alloys relevant to Fischer-Tropsch Synthesis: Bcc-(Cu)Fe(100) and fcc-(Fe)Cu(100)
, Article Surface and Interface Analysis ; Volume 45, Issue 7 , 2013 , Pages 1081-1087 ; 01422421 (ISSN) ; Fazeli, E ; Joshani, A ; Gholami, M ; Sharif University of Technology
Abstract
Direct CO dissociation is seen the main path of the first step in the Fischer-Tropsch Synthesis (FTS) on the reactive iron surfaces. Cu/Fe alloy film is addressed with various applications over face-centered-cubic (fcc)-Cu and body-centered-cubic (bcc)-Fe in the FTS, i.e. preventing iron carbide formation (through direct CO dissociation) by moderating the surface reactivity and facilitating the reduction of iron surfaces, respectively. In this study by density functional theory, the stable configurations of CO molecule on various Cu/Fe alloys over fcc-Cu(100) and bcc-Fe(100) surfaces with different CO coverage (25% and 50%) have been evaluated. Our results showed that the ensemble effect...
Adsorption and dissociation of hydrogen peroxide on small Pd xM3-x (M = Pt, Cu; X = 1-3) clusters: A hybrid density functional study
, Article Molecular Physics ; Volume 109, Issue 14 , May , 2011 , Pages 1797-1804 ; 00268976 (ISSN) ; Gobal, F ; Arab, R ; Sharif University of Technology
2011
Abstract
The adsorption and dissociation of H2O2 on small PdxM3-x (M=Pt, Cu; x = 1-3) clusters is investigated using the B3PW91 hybrid density functional method. Natural bond orbitals are analysed to obtain partial charges on atoms, dipole moments, bond orders, and hybrid orbitals of the PdxM3-x-H2O2 systems. The calculated adsorption energies are in the range of -0.32 to -2.12 eV. Generally, H2O2 adsorbs on top positions through one of its oxygen atoms and only in a few cases reacts with the cluster through both oxygen and hydrogen sides. In the latter case the cluster sites which are negatively charged interact with the hydrogen atoms. Interestingly, on the triplet Pd2Pt cluster, H2O2 dissociates...
Adsorption of carbon monoxide on SixGe4-x(x = 0-4) nano-clusters: A hybrid meta density functional study
, Article Molecular Physics ; Volume 108, Issue 10 , 2010 , Pages 1317-1327 ; 00268976 (ISSN) ; Gobal, F ; Sharif University of Technology
2010
Abstract
Theoretical study of carbon monoxide adsorption on SixGe4 - x(x = 0-4) nano-clusters has been carried out using advanced hybrid meta density functional method of Truhlar (MPW1B95). MG3 semi-diffuse (MG3S) and correlation consistent valence basis sets with relativistic core potential were employed to improve the results. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. The geometry, adsorption energy, charge distribution, and vibrational frequency of CO adsorption on all possible structures were investigated. The maximum vibrational...
A perspective on electrostatics in gas-solid fluidized beds: challenges and future research needs
, Article Powder Technology ; Volume 329 , 2018 , Pages 65-75 ; 00325910 (ISSN) ; Bi, X. T ; Grace, J. R ; Sharif University of Technology
Elsevier B.V
2018
Abstract
This paper provides a perspective on the current knowledge and potential areas of future research related to electrostatics in fluidized beds. Aspects addressed include characterization techniques, charge generation and dissipation mechanisms, interplay between the electrostatics and hydrodynamics, charge control methods, applications of tribo-electrostatic fluidization systems, and computational simulations which account for electrostatic charges. This is a complex research field involving fluid mechanics, powders and electrical physics, with potential rewards in terms of safety, process monitoring and new applications. © 2018 Elsevier B.V
A perspective on electrostatics in gas-solid fluidized beds: Challenges and future research needs
, Article 13th International Conference on Fluidized Bed Technology, CFB 2021, 10 May 2021 through 14 May 2021 ; 2021 , Pages 426-431 ; 9781771368506 (ISBN) ; Bi, X. T ; Grace, J. R ; Sharif University of Technology
GLAB Reactor and Fluidization Technologies
2021
Abstract
This paper provides a perspective on the current knowledge and potential areas of future research related to electrostatics in fluidized beds. Aspects addressed include characterization techniques, interplay between electrostatics and hydrodynamics, charge control methods, applications of tribo-electrostatic fluidization systems, and computational simulations which account for electrostatic forces, as well as other forces. This is a complex research field involving fluid mechanics, powders, and electrical physics. © 2021 CFB 2021 - Proceedings of the 13th International Conference on Fluidized Bed Technology. All rights reserved
Benchmarking of Monte Carlo model of Siemens Oncor® linear accelerator for 18MV photon beam: determination of initial electron beam parameters
, Article Journal of X-Ray Science and Technology ; Volume 27, Issue 6 , 2 January , 2020 , Pages 1047-1070 ; Hoseini Ghafarokhi, M ; Bolagh, R. S. M ; Haghparast, M ; Zarifi, S ; Nickfarjam, A ; Farhood, B ; Chow, J. C. L ; Sharif University of Technology
IOS Press
2020
Abstract
OBJECTIVE: This study aims to benchmark a Monte Carlo (MC) model of the 18 MV photon beam produced by the Siemens Oncor® linac using the BEAMnrc and DOSXYZnrc codes. METHODS: By matching the percentage depth doses and beam profiles calculated by MC simulations with measurements, the initial electron beam parameters including electron energy, full width at half maximum (spatial FWHM), and mean angular spread were derived for the 10×10 cm2 and 20×20 cm2 field sizes. The MC model of the 18 MV photon beam was then validated against the measurements for different field sizes (5×5, 30×30 and 40×40 cm2) by gamma index analysis. RESULTS: The optimum values for electron energy, spatial FWHM and mean...
Binding energy of bipartite quantum systems: Interaction, correlations, and tunneling
, Article Physical Review A ; Volume 101, Issue 1 , 2020 ; Bathaee, M ; Bakhshinezhad, F ; Rezakhani, A. T ; Bahrampour, A. R ; Sharif University of Technology
American Physical Society
2020
Abstract
We provide a physically motivated definition for the binding energy (or bond dissociation) of a bipartite quantum system. We consider coherently applying an external field to cancel out the interaction between the subsystems, to break their bond and separate them as systems from which no work can be extracted coherently by any cyclic evolution. The minimum difference between the average energies of the initial and final states obtained this way is defined as the binding energy of the system. We show that the final optimal state is a passive state. We discuss how the required evolution can be realized through a sequence of control pulses. The utility of our definition is illustrated through...
Bonding, structural and thermodynamic analysis of dissociative adsorption of H3O+ ion onto calcite (10 1 ¯ 4) surface: CPMD and DFT calculations
, Article Journal of Molecular Modeling ; Volume 23, Issue 12 , 2017 ; 16102940 (ISSN) ; Koleini, M. M ; Sharif University of Technology
Abstract
We used density functional theory (DFT) and Car-Parrinello molecular dynamics (CPMD) simulation to investigate the adsorption and bond formation of hydronium ion (H3O+) onto a (10 1 ¯ 4) calcite surface. For surface coverage of 25% to 100%, the nature of H3O+ interaction was explored through electron density and energetics in the context of bond critical points. The adsorbate–adsorbent structure was studied by simulation of pair correlation function. The results revealed that dissociation into water molecule(s) and proton(s) complements H3O+ ion(s) adsorbtion. The H2O molecule adsorbs onto the surface via its O atom, and interacts with surface calcium in a closed-shell mode; the H+ ion makes...
Carbon dioxide reforming of methane by pulsed glow discharge at atmospheric pressure: the effect of pulse compression
, Article Journal of Applied Physics ; Volume 101, Issue 12 , 2007 ; 00218979 (ISSN) ; Modarresi, H ; Sharif University of Technology
2007
Abstract
Methane reforming by carbon dioxide in pulsed glow discharge at atmospheric pressure is examined. The plasma pulse is compressed to less than 50 ns. This compression enables one to work at higher frequencies, over 3 kHz, without glow-arc transition. The main products of the reaction are synthetic gases (H2, CO) and C2 hydrocarbons. Approximately 42% of plasma energy goes to the chemical dissociation, when the reactant ratio is C O2 C H4 =1. At this point, the energy expense is less than 3.8 eV per converted molecule while reactant conversions are relatively high reaching to 55% (C H4) and 42% (C O2). The reactor energy performance even gets better at higher C O2 C H4 ratios. While energy...
Conversion of a weak organic acid to a super acid in the gas phase
, Article Journal of Physical Organic Chemistry ; Volume 21, Issue 2 , 2008 , Pages 112-118 ; 08943230 (ISSN) ; Tavasoli, E ; Sharif University of Technology
2008
Abstract
The effects of selected metal ions on the gas-phase acidity of weak organic acids have been explored using the DFT and Moller-Plesset Perturbation Theory (MP2) calculations. The three organic acids selected for this study were acetic acid (aliphatic), benzoic acid (aromatic), and glycine (amino acid). The acidities of these compounds are compared with the acidity of their Li +-, Na+-, and K+ -complexed species. The results indicate that upon complexation with Li+, Na+, and K+ at 298K, the gas-phase acidity of acetic acid, for example, varies from 345.3 to 218.8, 230.2, and 240.1 kcal/mol, respectively (i.e., its dissociation becomes much less endothermic). These values indicate that a weak...
DFT study of nitrogen monoxide adsorption and dissociation on Rh[sbnd]Cu nano clusters
, Article Journal of Alloys and Compounds ; Volume 695 , 2017 , Pages 1924-1929 ; 09258388 (ISSN) ; Nahali, M ; Gobal, F ; Sharif University of Technology
Abstract
Adsorption and dissociation of NO on RhxCu4-x(x = 0–4) nano clusters were investigated using density functional theory. Adsorption energy, total charge on NO, NO bond length, and NO vibrational frequency for various modes of NO adsorption were analyzed. Adsorption from the nitrogen end of NO on the Rh atom(s) of the clusters are more favored and adsorption energies are in the −1.02 eV to −2.59 eV range. NO binds stronger to Rh-Cu mixed clusters compared to pure Cu4 cluster, so N[sbnd]O bond is significantly weakened upon adsorption on the former. NO binding to more atoms of the clusters results in a corresponding decrease of the N[sbnd]O vibrational frequency. Dissociation of NO was also...
Dissociation of C-H molecular bond of methane by pulse shaped ultra-intense laser field
, Article Chemical Physics Letters ; Volume 560 , 2013 , Pages 60-65 ; 00092614 (ISSN) ; Irani, E ; Navid, H. A ; Dehghani, Z ; Anvari, A ; Sadighi Bonabi, R ; Sharif University of Technology
2013
Abstract
The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability
Dissociative ionization of methane in an elliptical pulse shaped laser field
, Article Journal of Molecular Structure ; Volume 1079 , January , 2015 , Pages 454-459 ; 00222860 (ISSN) ; Sadighi Bonabi, R ; Anvari, A ; Sharif University of Technology
Elsevier
2015
Abstract
The effect of strong femto-second laser pulses on the dissociation probability of methane has been investigated analytically in various arrangements. The ellipticity dependence of the dissociation probability at intensities from 1014 W cm-2 to 1016 W cm-2 for Ti:Sapphire laser is presented. A reliable calculation of the dissociation probability based on 3D time-dependent Schrodinger equation with an improved model of time-dependent density-functional theory is presented. These calculations are carried out for three different cases of elliptically polarized laser pulse, optimum convolution of dual short pulses, and two-color mixed nonresonant laser pulses. It is found that the rescattering...
Does gold cluster promote or scavenge radicals? A controversy at DFT
, Article Journal of Physical Organic Chemistry ; 2017 ; 08943230 (ISSN) ; Kassaee, M. Z ; Fattahi, A ; Sharif University of Technology
John Wiley and Sons Ltd
2017
Abstract
Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au3 cluster on RO• vs its impacts on RO-H bond dissociation enthalpy, at B3LYP/ LACVP+* level (RH, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, and phenyl). In the presence of Au3 cluster, bond dissociation enthalpy of O-H bond and the spin density at the RO• oxygen are reduced dramatically. These are clear evidences for both the Au3 facilitation of the RO-H bond breakage and its scavenging of RO• radical. Since O-Au anchoring...
Does gold cluster promote or scavenge radicals? A controversy at DFT
, Article Journal of Physical Organic Chemistry ; Volume 31, Issue 3 , 2018 ; 08943230 (ISSN) ; Kassaee, M. Z ; Fattahi, A ; Sharif University of Technology
John Wiley and Sons Ltd
2018
Abstract
Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au3 cluster on RO• vs its impacts on RO–H bond dissociation enthalpy, at B3LYP/ LACVP+* level (R═H, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, and phenyl). In the presence of Au3 cluster, bond dissociation enthalpy of O–H bond and the spin density at the RO• oxygen are reduced dramatically. These are clear evidences for both the Au3 facilitation of the RO–H bond breakage and its scavenging of RO• radical. Since O–Au...
Effect of nanostructuring on thermal stability and decomposition of aluminium titanate (Al2TiO5): a phase transformation study
, Article Materials Characterization ; Volume 173 , 2021 ; 10445803 (ISSN) ; Madaah Hosseini, H. R ; Amutha, C ; Ramakrishna, S ; Sharif University of Technology
Elsevier Inc
2021
Abstract
As a refractory ceramic, the thermal instability of aluminium titanate (AT or Al2TiO5) has been in the crosshairs of research works in recent years. The studies have indicated that different parameters such as atmosphere, grain size, additives, oxygen pressure, and synthesis method can bilaterally affect the thermal decomposition of AT ceramic and resultant physicomechanical properties. In the present study, the AT nanostructure was synthesized by a citrate sol-gel method and influence of nanostructuring nature on its thermal instability and reaction pathway was explored in some details. It was shown that the reduction of grain size down to 30 nm can destabilize AT, so that the reaction...
Efficient photo-dissociation of CH4 and H2CO molecules with optimized ultra-short laser pulses
, Article AIP Advances ; Volume 5, Issue 11 , 2015 ; 21583226 (ISSN) ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
American Institute of Physics Inc
2015
Abstract
The fragmentation dynamics of CH4 and H2CO molecules have been studied with ultra-short pulses at laser intensityof up to 1015Wcm-2. Three dimensional molecular dynamics calculations for finding the optimized laser pulses are presented based on time-dependent density functional theory and quantum optimal control theory. A comparison of the results for orientation dependence in the ionization process shows that the electron distribution for CH4 is more isotropic than H2CO molecule. Total conversion yields of up to 70% at an orientation angle of 30o for CH4 and 65% at 900 for H2CO are achieved which lead to enhancement of dissociation probability
Electronic structure of some thymol derivatives correlated with the radical scavenging activity: Theoretical study
, Article Food Chemistry ; Vol. 165, issue , Dec , 2014 , p. 451-459 ; Jebeli Javanb, M ; Sharif University of Technology
Abstract
Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of upmost importance in the living cell. Thymol derivatives exhibit various antioxidant activities and potential health benefits. Exploration of structure-radical scavenging activity (SAR) was approached with a wide range of thymol derivatives. To accomplish this task, the DPPH experimental assay along with quantum-chemical calculations were also employed for these compounds. By comparing the structural properties of the derivatives of interest, their antioxidant activity was explained by the formation of an intramolecular hydrogen bond and the presence of unsaturated double bond (–CHdouble bond; length...
Electrostatically defying cation-cation clusters: Can likes attract in a low-polarity environment?
, Article Journal of Physical Chemistry A ; Volume 117, Issue 38 , 2013 , Pages 9252-9258 ; 10895639 (ISSN) ; Ramezani, M ; Fattahi, A ; Kass, S. R ; Sharif University of Technology
2013
Abstract
Like-charge ion pairing is commonly observed in protein structures and plays a significant role in biochemical processes. Density functional calculations combined with the conductor-like polarizable continuum model were employed to study the formation possibilities of doubly charged noncovalently linked complexes of a series of model compounds and amino acids in the gas phase and in solution. Hydrogen bond interactions were found to offset the Coulombic repulsion such that cation-cation clusters are minima on the potential energy surfaces and neither counterions nor solvent molecules are needed to hold them together. In the gas phase the dissociation energies are exothermic, and the...
Experimental and computational bridgehead C-H bond dissociation enthalpies
, Article Journal of Organic Chemistry ; Volume 77, Issue 4 , January , 2012 , Pages 1909-1914 ; 00223263 (ISSN) ; Lis, L ; Tehrani, Z. A ; Marimanikkuppam, S. S ; Kass, S. R ; Sharif University of Technology
Abstract
Bridgehead C-H bond dissociation enthalpies of 105.7 ± 2.0, 102.9 ± 1.7, and 102.4 ± 1.9 kcal mol -1 for bicyclo[2.2.1]heptane, bicyclo[2.2.2]octane, and adamantane, respectively, were determined in the gas phase by making use of a thermodynamic cycle (i.e., BDE(R-H) = ΔH° acid(H-X) - IE(H •) + EA(X •)). These results are in good accord with high-level G3 theory calculations, and the experimental values along with G3 predictions for bicyclo[1.1.1]pentane, bicyclo[2.1.1]hexane, bicyclo[3.1.1]heptane, and bicyclo[4.2.1]nonane were found to correlate with the flexibility of the ring system. Rare examples of alkyl anions in the gas phase are also provided