An-Najah National University

Dr. Mohammed S. Abu-Jafar Blog


  • Monday, March 26, 2001
  • Structural and electronic structure properties of FeSi: the driving force behind the stability of the B20 phase
  • Published at:Not Found
  • We present the results of a first-principles pseudopotential plane-wave study for the structural properties of the ε-FeSi (B20), NaCl (B1) and CsCl (B2) structures of FeSi. The calculations were performed using the local density and the generalized gradient approximations (LDA and GGA), for the exchange-correlation potential. The electronic structures of the B1 and B2 phases have been similarly investigated. These calculations have enabled us to identify the driving force behind the crystallization of FeSi in the B20 phase. Both the B1 and B2 phases are found to be semimetallic, with the Fermi energy lying in a pseudo-band-gap. The B20 structure is predicted to become unstable with respect to the B2 phase at a moderate pressure, of 13.5 and 10.9 GPa according to the GGA and LDA calculations, respectively.
    J. Phys.: Condens. Matter 13 2807-2815
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  • Sunday, October 1, 2000
  • FP-LAPW and pseudopotential calculations of the structural phase transformations of GaN under high-pressure
  • Published at:Solid State Communications 116 (2000) 389±393
  • FP-LAPW and pseudopotential approaches have been used to investigate the structural phase transformations of GaN under high-pressure. In these calculations the local density and generalized gradient approximations (LDA and GGA) for the exchange-correlation potential have been used. Moreover, the electronic structure of the wurtzite (WZ), rocksalt (RS) and zinc-blende (ZB) phases of GaN have been calculated. The GGA result for the transition pressure of the WZ→RS transition is of 42.3 GPa, which is in very good agreement with the X-ray absorption spectroscopy value of 47 GPa. The gradient corrections to the LDA, included via GGA, have small, but not negligible, effects on the properties studied. RS-GaN is predicted to be an indirect-band-gap semiconductor, with a band-gap of 1.7 eV.
    Solid State Communications, Volume 116, Issue 7, 16 October 2000, Pages 389-393
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  • Thursday, January 1, 1998
  • The instability of the cinnabar phase of ZnS under high pressure
  • Published at:Not Found
  • We present the results of a theoretical study of the structural phase transformations of ZnS under high pressure, using first-principles pseudopotential and full-potential linear muffin-tin orbital methods, in which the semicore Zn d electrons are treated as valence states. The zinc-blende, NaCl and cinnabar forms of ZnS have been considered. The structural properties and the band structures of these systems have also been studied. In the case of the FP-LMTO approach, an optimal choice of the empty spheres, atomic radii and filling percentage is introduced, which gives results in excellent agreement with those of the present pseudopotential method. It has been found that cinnabar phase is not a stable phase in ZnS under high pressure. The cinnabar phase is predicted to be a semiconductor with a direct band gap of about 3.6 eV.
    J. Phys.: Condens. Matter 10 5069-5080   1998
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  • Monday, January 1, 1996
  • A Fifth-order Multiperturbation Derivation of the Energy Coefficients of Polyatomic Molecules
  • Published at:An-Najah J. Res, Vol. 4, No.10 (1996)
  • A multiperturbation theory has been developed for molecular systems. In the present paper we extend this theory to fifth order in the energy. The "bare-nucleus" hydrogenic function is chosen as the zero-order wave function rather than the more customary hartree-fock function. With this choice the multiperturbation wave functions are independent of the nuclear charges and of the total number of nuclear centers and electrons for the molecule and are thus completely transferable to other systems. Making the simplest possible choice, we describe an n-electron, m-center polyatomic molecule as n "hydrogenic" electrons on a single center perturbed by electron-electron and electron-nucleus coulomb interactions. With this choice of zero-order Hamiltonian (H0) the first-order wave function for any polyatomic molecule will consist entirely of two-electron, one-center and one-electron, two-center first-order wave functions. These are exactly transferable from calculations on He-like and H2-like systems. To calculate the
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Mohammed Abu-Jafar
Computaional Condensed Matter Physics
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