Wael S Abdel Halim | Zagazig University (original) (raw)

Papers by Wael S Abdel Halim

International Journal of Modern Physics C, 1998

An empirical scheme for implementation of bond functions in heteronuclear diatomics is suggested ... more An empirical scheme for implementation of bond functions in heteronuclear diatomics is suggested and applied to HeBe using universal even-tempered functions. The effects of bond functions and core-correlation energy on the interaction potential of HeBe calculated at the uncorrelated (SCF) and correlated (MBPT and CC) levels are examined. The results confirm that an accuracy of sub μ Hartree level can be obtained using even-tempered functions with s-, p-, and d- symmetry and that bond functions of size {4s2p} for He and {6s3p} for Be recovers 100% of energy lowering obtained from the addition of 10d atom-centered functions to He and 13d atom centred functions to Be. The various treatments of the electron correlation, conclude that the system is interacting weakly with a well depth from 14.5–24.7 μE h at a separation near 9.1a0 compared with 20.7–25.5 μE h previously reported with a rather limited basis set. The most reliable well depth corrected for BSSE (19.0 μE h ) was obtained at ...

Molecular Simulation, 2015

Abstract The effects of mechanical bending on tuning the hydrogen storage of titanium functionali... more Abstract The effects of mechanical bending on tuning the hydrogen storage of titanium functionalised (4,0) carbon nanotube have been assessed using density functional theory calculations with reference to the ultimate targets of the US Department of Energy (DOE). The assessment has been carried out in terms of physisorption, gravimetric capacity, projected densities of states, statistical thermodynamic stability and reaction kinetics. The Ti atom binds at the hollow site of the hexagonal ring. The average adsorption energies (−0.54 eV) per hydrogen molecule meet the DOE target for physisorption (−0.20 to −0.60 eV). The curvature attributed to the bending angle has no effect on the average adsorption energies per H2 molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 9.0 wt%. The reactions of the deformed (bent) carbon nanotube have higher probabilities of occurring than those of the un-deformed carbon nanotube. The Gibbs free energies, enthalpies and entropies meet the ultimate targets of the DOE for all temperatures and pressures. The closest reactions to zero free energy occur at (378.15 K/2.961 atm.) and reverse at (340 and 360 K/1 atm.). The translational component is found to exact a dominant effect on the total entropy change with temperature. Favourable kinetics of the reactions at the temperatures targeted by DOE are reported regardless of the applied pressure. The more preferable thermodynamic properties assigned to the bending nanotube imply that hydrogen storage can be improved compared to the nonbending nanotube.

Quantum Matter, 2014

ABSTRACT Ab initio molecular electronic structure computations have been performed employing DFT ... more ABSTRACT Ab initio molecular electronic structure computations have been performed employing DFT and TD-DFT methodologies to optimize the performance of two types of DSSCs. This was done by tuning the frontier orbital energy gaps, adding low cost transition metal atoms (Zn, Ni, Fe, Ti) to the porphyrin donor, and strongly activating electron donating groups (NMe2 ) to the fullerene acceptor. The results reveal that cell efficiency has been significantly enhanced by metal functionalization of the donor, and the electron donating capabilitiy of the acceptor. While Ti-porphyrin was found to be the most efficient dye sensitizer for DSSCs based on porphyrin donors and substituted fullerene acceptors, Fe-porphyrin was found to be the most efficient sensitizer for DSSCs based on porphyrin donors and a series of oxide semiconductor acceptors. Fe dye can sensitize several oxide semiconductor acceptors in [Co(dmb)3]n+ redox electrolyte, and cell efficiencies of Ti dyads can exceed (4.8%). The metal atoms and the electron donating groups facilitate rapid electron injection from the donor moiety to the acceptor moiety and narrow the band gaps of both of the donors and acceptors so that the density of states near the Fermi levels scales linearly with the photovoltaic conversion efficiency. The introduction of low cost Fe and Ti to the free base porphyrin leads to more active non linear optical performance, stronger response to the external electric field, and induces higher photo-to-current conversion efficiency. Fe and Ti also red shift the electronic absorption bands of the free base porphyrin, and make it a potential candidate for harvesting light in the entire region of solar spectrum.

Journal of Molecular Structure: THEOCHEM, 2005

Solid State Communications, 2008

ABSTRACT The adsorption properties Of Cl(2) molecules adsorbed on Li and Na atoms supported on va... more ABSTRACT The adsorption properties Of Cl(2) molecules adsorbed on Li and Na atoms supported on various sites of MgO and CaO (100) surfaces have been examined at the DFT/B3LYP level of theory using the embedded cluster model. By comparison, the adsorption on the clean surfaces of the support has been investigated. Our calculations predict weakening of the Cl(2) bond due to the presence of the alkali metals, reflected by an elongation of the Cl(2) bond by 0.64 A. Although the regular and defective sites are stronger binding sites in CaO (001) than in MgO (001), the interaction energy decreases as the atomic number of alkali atoms (Li and Na) increases. Metal atoms bind more strongly on the defect sites. The MgO and CaO (001) surfaces not only serve as the supports of Li and Na atoms but also participate in the interaction with Cl(2) molecule. Charge transfer takes place from the oxide surface to the adsorbed metal. (c) 2008 Elsevier Ltd. All rights reserved.

Journal of Molecular Modeling, 2011

The size of the cations (either Ca(2+), Sr(2+), Ga(+), or Au(+)) at the F(A1)-type color centers ... more The size of the cations (either Ca(2+), Sr(2+), Ga(+), or Au(+)) at the F(A1)-type color centers on the (100) surface of LiCl crystal plays an important role in the optical properties of this surface. In this work, double-well potentials at this surface were investigated using ab initio quantum mechanical methods. Quantum clusters were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surface, and the ions that were the nearest neighbors to the F(A1) site were allowed to relax to equilibrium. The calculated Stokes-shifted optical transition bands, optical-optical conversion efficiency, and relaxed excited states of the defect-containing surface, as well as the orientational destruction of the color centers, recording sensitivity, exciton (energy) transfer, and the Glasner-Tompkins empirical relation were all found to be sensitive to the size of the dopant cation.

International Journal of Quantum Chemistry, 2012

International Journal of Quantum Chemistry, 2000

ABSTRACT Van der Waals interaction potentials of the square planar D4h and regular tetrahedral Td... more ABSTRACT Van der Waals interaction potentials of the square planar D4h and regular tetrahedral Td configurations of He4 were examined at the matrix Hartree–Fock, many-body perturbation theory, coupled-cluster theory, and configuration interaction levels of ab initio theory. Potential energy minima, pairwise and nonpairwise additivity, group theoretical parameters, and isotope substitution effects were found to uniquely characterize these interactions. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 76: 10–22, 2000

Chemical Physics, 2006

The oxidation states of Thallium in FA1 Tl+n (n=1,3) color centers at the (100) surface of NaCl p... more The oxidation states of Thallium in FA1 Tl+n (n=1,3) color centers at the (100) surface of NaCl play important role in laser light generation and adsorbate–substrate interactions. Double-well potentials at these surfaces are investigated by using quantum mechanical ab initio methods. Quantum clusters of variable sizes were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of

Applied Surface Science, 2007

The adsorption of carbon monoxide at the defect-free (100), (110) and (210) five-atomic layer sla... more The adsorption of carbon monoxide at the defect-free (100), (110) and (210) five-atomic layer slab of the three oxides: MgO, CaO, and SrO has been investigated using the periodic Hartree–Fock level of ab initio theory, together with the 1×1 supercell model. All the calculated CO/oxide interaction energies exhibit exothermic character. The HF interaction energies increase monotonically in the order MgO<CaO<SrO. The surface morphology of adsorbate/substrate interaction is confirmed by considering relaxation energies, Mulliken population analysis, charge density contours, and electrostatic potential maps.

Applied Surface Science, 2004

Abstract The dissociation of water molecule at the defect free (0 0 1), (1 1 0) and (2 1 0) five-... more Abstract The dissociation of water molecule at the defect free (0 0 1), (1 1 0) and (2 1 0) five-layer films of the title oxides has been investigated using the periodic HF and DFT levels of ab initio theory together with the 1×1 supercell model in which two water molecules were added to each supercell, one at each side of the film. The water/oxide reaction energies calculated at the HF-level exhibit endothermic character at the (0 0 1) film and exothermic character at the (1 1 0) and (2 1 0) films, while those calculated at the DFT-level always exhibit exothermic character except for the (0 0 1) film of MgO. The interaction energies increase monotonically in the order (0 0 1)

Applied Surface Science, 2009

ABSTRACT The adsorption properties of CO molecules adsorbed on Ni, Pd, Cu and Ag atoms deposited ... more ABSTRACT The adsorption properties of CO molecules adsorbed on Ni, Pd, Cu and Ag atoms deposited on O(2) , F and F(+) sites of MgO, CaO, SrO and BaO terrace surfaces have been studied by means of density functional calculations and embedded cluster model. The examined clusters were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. The adsorption properties of CO have been analyzed with reference to the basicity of the oxide support, bond order conservation energy, pairwise and non-pairwise additivity, associative adsorption, electrostatic potentials, and orbital interactions. CO adsorption on an oxide support is drastically enhanced when CO is adsorbed on a metal deposited on this support. A dramatic change is found, and explained, when one compares the CO binding energy to O(2) and F sites. The formation of a strong bond at the support metal interface has a considerable consequence on the metal-CO binding energy. The binding of CO is dominated by the metal-CO pairwise additive term, and the non-additivity term increases with increasing the basicity of the support. While the classical contributions to the electrostatic interactions are quite similar for the deposited metals, they are quite dissimilar when going from defect-free to defect-containing surfaces. The adsorption properties correlate linearly with the basicity and energy gaps of the oxide support where the electrostatic potential generated by the oxide modifies the physical and chemical properties of the adsorbed metal and therefore its reactivity versus the CO adsorbate.

Applied Surface Science, 2012

Journal of Molecular Structure: THEOCHEM, 2001

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t We have analyzed the magnetic and binding properties of Ni, Cr, Mo, and Pt metals deposited on the defect free and defect containing surfaces of MgO by means of density functional theory calculations and embedded cluster model. Clusters of moderate sizes with no border anions, to avoid artificial polarization effects, were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. Spin quenching occurs for Cr and Mo complexes at the defect free (terrace) surface, and Cr, Mo, and Pt complexes at the defect containing ''pit'' divacancy surface. The binding energies of the metals are significantly enhanced on the cationic vacancy end of the divacancy. The adsorption energies of the low spin states of spin quenched complexes are always greater than those of the high spin states. The metal–support interactions stabilize the low spin states of the adsorbed metals with respect to the isolated metals, but the effect is not always enough to quench the spin. The encountered variations in magnetic properties of free metals and of metal complexes are correlated with the energy gaps of the frontier orbitals. Spin contamination affect the adsorbate–substrate distances, Mulliken charges, Mulliken spin densities, natural charge, natural orbital population, and provide rationalization for the reported magnetic and binding properties. The electrostatic potential energy curves provide clearer understanding of the nature of magnetic and binding interactions. The magnetic and binding properties of a single metal atom adsorbed on a particular surface result from a competition between Hund's rule for the adsorbed metal, and the formation of a chemical bond at the interface.

Ab initio molecular electronic structure computations have been performed employing DFT and TD-DF... more Ab initio molecular electronic structure computations have been performed employing DFT and TD-DFT method-ologies to optimize the performance of two types of DSSCs. This was done by tuning the frontier orbital energy gaps, adding low cost transition metal atoms (Zn, Ni, Fe, Ti) to the porphyrin donor, and strongly activating electron donating groups (NMe 2) to the fullerene acceptor. The results reveal that cell efficiency has been significantly enhanced by metal functionalization of the donor, and the electron donating capabilitiy of the acceptor. While Ti-porphyrin was found to be the most efficient dye sensitizer for DSSCs based on porphyrin donors and substituted fullerene acceptors, Fe-porphyrin was found to be the most efficient sensitizer for DSSCs based on porphyrin donors and a series of oxide semiconductor acceptors. Fe dye can sensitize several oxide semiconductor acceptors in [Co(dmb) 3 ] n+ redox electrolyte, and cell efficiencies of Ti dyads can exceed (4.8%). The metal atoms and the electron donating groups facilitate rapid electron injection from the donor moiety to the acceptor moiety and narrow the band gaps of both of the donors and acceptors so that the density of states near the Fermi levels scales linearly with the photovoltaic conversion efficiency. The introduction of low cost Fe and Ti to the free base porphyrin leads to more active non linear optical performance, stronger response to the external electric field, and induces higher photo-to-current conversion efficiency. Fe and Ti also red shift the electronic absorption bands of the free base porphyrin, and make it a potential candidate for harvesting light in the entire region of solar spectrum.

An attempt has been made to analyze the spin quenching properties of Mn, as a representative of t... more An attempt has been made to analyze the spin quenching properties of Mn, as a representative of transition metals, in MnÁMgO, MnÁCaO, OCÁMnÁMgO, and OCÁMnÁCaO complexes formed at the regular (001) surfaces of MgO and CaO, as well as the adsorption of CO on Mn deposited on MgO and CaO by means of hybrid density functional theory calculations and embedded cluster model. Clusters of moderate sizes were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. A test has been made to examine the effect of artificial flow of charge. While the spin states of Mn in MnÁMgO and MnÁCaO complexes are preserved, the combined effects of adsorbate and substrate in OCÁMnÁMgO and OCÁMnÁCaO complexes are strong enough to favor the low spin states and to quench the spin. The deposited Mn atoms enhance the adsorption of CO on MgO and CaO surfaces. The significant weakening of bond strength between OC and Mn in complexes supports the concept of bond order conservation. The relation between the strength of CO adsorption and the basicity of the support is verified. The natural bond orbital analysis reveals that the electronic structure of the adsorbed metal represents a qualitative change with respect to that of the free metal. The effects of spin contamination on the geometry, Mulliken charges, and adsorption energy are examined. The binding of CO precursor is dominated by the E(i) MnÁÁÁCO pairwise additive components in MgO and CaO complexs, and the role of the support is not restricted to supporting the metal. The adsorbed CO molecules exhibit no remarkable deviation from linearity. Finally, relations are established between the process of spin quenching and the energy gaps between frontier orbitals. The results show that the spin state of adsorbed metal atoms on oxide supports and the role of precursor molecules on the magnetic and binding properties of complexes need to be explicitly taken into account. V

The F A1 :Cs C and F A2 :Li C color centers at the flat, edge and corner surfaces of AgBr play im... more The F A1 :Cs C and F A2 :Li C color centers at the flat, edge and corner surfaces of AgBr play important roles in laser light generation and color image formation. These two applications are investigated simultaneously by using quantum mechanical ab initio methods. As far as laser light generation is concerned, the calculated Stokes shifts suggest that laser activity is sensitive to the simultaneous effects of the vibrational coupling mode, the impurity cation, the coordination number of the surface ion, and the choice of the basis set centered on the anion vacancy. The F A1 :Cs C and F A2 :Li C color centers are suitable laser defects. The dependence of orientational destruction, recording sensitivity and exciton (energy) transfer on the impurity cation and the coordination number of the surface ion is clarified. The Glasner–Tompkins empirical rule is generalized to include the impurity cation and the coordination number of the surface ion. As far as color image formation is concerned, the supersensitizer was found to increase the sensitizing capabilities of two primary dyes in the excited states. Color image formation was found to be sensitive to the coordination number of the surface ion and the type of the impurity cation. On the basis of quasi Fermi levels, the difference in the sensitizing capabilities between the examined dyes in the excited states was determined.