http://blogs.najah.edu/author/abu-jafar An-Najah Blogs :: Dr. Mohammed S. Abu-Jafar Blog en-us Fri, 26 Apr 2024 08:19:28 IDT Fri, 26 Apr 2024 08:19:28 IDT [email protected] [email protected] http://blogs.najah.edu/staff/abu-jafar/article/Structural-and-electronic-structure-properties-of-FeSi-the-driving-force-behind-the-stability-of-the-B20-phasePublished ArticlesWe present the results of a first-principles pseudopotential plane-wave study for the structural properties of the -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 135 and 109GPa according to the GGA and LDA calculations respectively J Phys: Condens Matter 13 2807-2815 http:dxdoiorg1010880953-89841312305http://blogs.najah.edu/staff/abu-jafar/article/FP-LAPW-and-pseudopotential-calculations-of-the-structural-phase-transformations-of-GaN-under-high-pressurePublished ArticlesFP-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 WZRS transition is of 423GPa which is in very good agreement with the X-ray absorption spectroscopy value of 47GPa 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 17eV Solid State Communications Volume 116 Issue 7 16 October 2000 Pages 389-393 http://blogs.najah.edu/staff/abu-jafar/article/Calculation-of-Ground-State-Energy-for-Linear-HeH2-through-Fifth-Order-United-Atom-TreatmentPublished ArticlesIn this paper the nonrelativistic energies of the linear HeH2 molecular ion have been computed using the multiperturbation theory for the ground state through fifth order The results are very encouraging compared to the variational calculationshttp://blogs.najah.edu/staff/abu-jafar/article/The-instability-of-the-cinnabar-phase-of-ZnS-under-high-pressurePublished ArticlesWe 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 36 eV J Phys: Condens Matter 10 5069-5080 1998http://blogs.najah.edu/staff/abu-jafar/article/A-Fifth-order-Multiperturbation-Derivation-of-the-Energy-Coefficients-of-Polyatomic-MoleculesPublished ArticlesA 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 first-order and second order correction for the wave function of any polyatomic molecule we need the first-order and second-order correction for a two-electron atomic wave function the first-order and second-order correction for a one-electron diatomic molecular wave function and some additional mixed second-order corrections The wave functions necessary will be two-center one-electron at most The second-order wave function for a polyatomic molecule contains additional contributions which cannot be obtained from the simple subsystems but represent multiple perturbation contributions which are two electron diatomic and one-electron triatomic in character The expressions for the multiperturbation energy-expansion coefficients through fifth order are derivedhttp://blogs.najah.edu/staff/abu-jafar/article/Multiperturbation-approach-to-potential-energy-surfacesPublished ArticlesIn Z-dependent perturbation theory the lowest-order wave functions for a polyatomic molecule are not only independent of the nuclear charges but also of the total number of nuclear centers and electrons in the molecule The complexity of the problem is then determined by the highest order retained in the calculation Choosing the simplest possible unperturbed Hamiltonian we describe an n-electron m-center polyatomic molecule as n hydrogenic electrons on a single center perturbed by electronelectron and electronnucleus Coulomb interactions With this H0 the first-order wave function for any polyatomic molecule will be a sum of products of hydrogenic orbitals with either two-electron one-center or one-electron two-center first-order wave functions These first-order wave functions are obtained from calculations on He-like and H2 1-like systems Similarly the nth-order wave function decouples so that the most complex terms are just the nth-order wave functions of all the p-electron q-center subsystems p1q5n12 contained in the molecule We illustrate applications of this method with some results complete through third order in the energy for H3 1-like molecules These are compared with accurate variational results available in the literature We conclude that through this order this perturbation approach is capable of yielding results comparable in accuracy to variational calculations of moderate complexity The ease and efficiency with which such results can be obtained suggests that this method would be useful for generating detailed potential energy surfaces for polyatomic molecules 1995 American Institute of Physics J Chem Phys Vol102 No 12 22 March 1995