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Öğe Ab initio search for global minimum structures of neutral and anionic hydrogenated Li-5 clusters(Elsevier Science Bv, 2013) Muz, Iskender; Atis, Murat; Canko, Osman; Yildirim, Erdem KamilThe structure and some electronic properties of neutral and anionic Li5Hn (n = 0-6) clusters have been studied by using the stochastic search method with the B3LYP/6-31G level of theory. After searching possible isomers, first few isomers with the lowest energy have been recalculated by the B3LYP/6-311G++(2d,2p) and CCSD(T)/6-311G++(2d, 2p) level of theory. The method used in this study has been compared with the previously reported ab initio calculations, and its reliability has been confirmed. The anionic Li5Hn (n = 0-6) clusters are reported in this study for the first time. Our results show that in general, stability increases with increasing number of hydrogen atoms. The fragmentation energies of hydrogenated Li-5 clusters are easier to fragmentation the two hydrogen atoms than one hydrogen atom in hydrogenated clusters, and it is too high for the reversible hydrogen storage systems. (C) 2013 Elsevier B.V. All rights reserved.Öğe Electronic structure and magnetic properties of PbMO3 (M = Fe, Co, Ni) magnetic perovskites: An ab initio study(World Scientific Publ Co Pte Ltd, 2014) Erkisi, Aytac; Yildirim, Erdem Kamil; Gokoglu, GokhanWe present the electronic, magnetic and structural properties of the magnetic transition metal oxides PbMO3 (M= Fe, Co, Ni) in cubic perovskite structure. The calculations are based on the density functional theory (DFT) within plane-wave pseudopotential method and local spin density approximation (LSDA) of the exchange-correlation functional. Onsite Coulomb interaction is also included in calculations (LSDA + U). The systems are considered in ferromagnetic (FM) and G-type antiferromagnetic (G-AFM) order. FM structures are energetically more favored than G-AFM and than non-magnetic states for all the systems studied. The spin-polarized electronic band structures show that all the structures have metallic property in FM order without Hubbard-U interaction (U-eff = 0). However, the inclusion of on-site Coulomb interaction (U-eff = 7 eV) opens a semiconducting gap for majority spin channel of PbFeO3 and of PbNiO3 resulting in a half-metallic character. PbCoO3 system remains as metallic with LSDA + U scheme. Bonding features of all structures are largely determined by the hybridizations between O-p and d-states of transition metal atoms. The partial magnetic moment of Fe atom in PbFeO3 is enhanced by inclusion of Hubbard-U interaction (2.55 mu B double right arrow 3.78 mu B). Total magnetic moments of half-metallic PbFeO3 and of PbNiO3 compounds are very close to integer values.Öğe First-principles investigation of LaGaO3 and LaInO3 lanthanum perovskite oxides(Taylor & Francis Ltd, 2016) Erkisi, Aytac; Gokoglu, Gokhan; Surucu, Gokhan; Ellialtioglu, Recai; Yildirim, Erdem KamilAmong the class of ABO(3)-type perovskite oxides, LaMO3 (M=Ga and In) compounds are investigated in cubic (Pm-3m), tetragonal (P4mm), hexagonal (P-3m1), rhombohedral (R-3c) and orthorhombic (Pbnm) phases using generalised gradient approximation (GGA) within the density functional theory. On-site Coulomb interaction is also included in the calculations (GGA+U). After the determination of the stable phase, phase transition pressures have also been calculated. Then, their full structural, mechanical, electronic, optical and vibrational properties have been studied in stable orthorhombic (Pbnm) phase. Both compounds are non-magnetic insulators in their ground states. The energy gaps (E-g) of LaGaO3 and LaInO3 compounds have been found as 3.14 and 2.55eV, respectively. The calculated elastic constants and phonon dispersion curves confirm the stability of orthorhombic phase mechanically and dynamically.Öğe Search for the Global Minimum Structures of AlB3H2n (n=0-6) Clusters(Wiley-Blackwell, 2015) Muz, Iskender; Canko, Osman; Atis, Murat; Yildirim, Erdem KamilThe global minimum structures of AlB3H2n (n=0-6) clusters are determined using the stochastic search method at the B3LYP/6-31G level of theory. These initially specified geometries are recalculated using B3LYP and CCSD(T) methods using the 6-311++G(**) basis set. The structural and electronic properties of the two lowest-lying isomers are presented. The structural parameters obtained for aluminum borohydride are compared with the experimental and theoretical results. The H-2 fragmentation energies of the most stable isomers are investigated. Chemical bonding analyses for the global minimum of AlB3H2n (n=0-6) clusters are performed using the adaptive natural density partitioning method. (c) 2014 Wiley Periodicals, Inc.Öğe Structural and computational characterization of 4 ',4 ',6 ',6 '-tetrachloro-3-(2-methoxyethyl)-3H,4H-spiro-1,3,2-benzoxaza phosphinine-2,2 '-[1,3,5,2,4,6]triazatriphosphinine(Elsevier, 2016) Isiklan, Muhammet; Yildirim, Erdem Kamil; Atis, Murat; Sonkaya, Omer; Cosut, BunyeminIn this study a new monospirocyclic phosphazene derivative, 4',4',6',6'-tetrachloro-3-(2-methoxyethyl)3H,4H-spiro [1,3,2-benzoxazaphosphinine-2,2'- [1,3,5,2,4,6] triazatriphosphinine] (SP1) was synthesized from the reaction of hexachlorocyclotriphosphazene (N3P3CI6) with N/0 donor-type, 2-{[(2-Metoxyethyl) amino]methylphenol. The structural investigations of the compound were verified by elemental analyses, MS, FFIR, 1H, 13C, 11 --P NMR spectroscopy and the single crystal X-ray diffraction analysis. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (DFT) using 6-311++G (d, p) basis set. The complete assignments of all vibrational modes were performed on the basis of the total energy distributions (TED). Isotropic chemical shifts (31P, 1H and 13C NMR) were calculated using the gauge-invariant atomic orbital (GIAO) method. Theoretical calculations of bond parameters, harmonic vibration frequencies and nuclear magnetic resonance are in good agreement with experimental results. The electrophilic and nucleophilic attack centers in SP1 were predicted with the local softness values (sit, and si) of individual atoms and it is confirmed that P atoms of the PCl2 groups are nucleophilic attack centers. (C) 2016 Elsevier B.V. All rights reserved.
