Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Start date: 2020Subject: search.filters.subject.Density Functional Theory

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Now showing 1 - 5 of 5
  • Article
    Dimensionality Effects in Anisotropic Single Layers TiSe5 and TiTe5: a Comparative Study of 2D Sheets and 1D Nanochains
    (IOP Publishing Ltd, 2026) Can Dogan, Kadir; Kutay Tamdogan, Omer; Bozkurt, Yagmur; Cetin, Zebih; Yagmurcukardes, Mehmet
    In this study, we present a comprehensive first-principles investigation of the structural, vibrational, and electronic properties of titanium pentachalcogenide structures in both two-dimensional (2D) and one-dimensional (1D) nanochain (NC) forms. Total energy and geometry optimizations reveal that the 2D TiX5 (X = Se, Te) structures exhibit in-plane anisotropy arising from the trigonal prismatic TiX3 units interconnected via the chalcogenide chains. Phonon band dispersions and elastic tensor elements confirm the dynamical and mechanical stability of the 2D layers, respectively. Electronically, while TiTe5 is a metal, TiSe5 possesses direct band gap semiconducting behavior. In addition, free-standing 1D NC counterparts, which are sub-units of the 2D structures, are investigated by means of their stability. Three stable 1D NCs, namely TiTe5-NC, TiSe7-NC, and TiTe7-NC, are found to be composed of edge-sharing TiX6-like units with either five- or seven-fold coordination. The dynamically stable 1D NCs are shown to be semiconductors with relatively larger band gaps as compared to 2D layers. Predicted Raman spectra reveal clear signatures of vibrational mode evaluations as a result of quantum confinement from the 2D layer to the 1D NC. Moreover, finite-temperature ab-initio quantum molecular dynamics simulations at 300 K confirm the thermal stability of both the 2D TiX5 layers and 1D NC derivatives, showing that the Ti-based systems retain their structural integrity under ambient conditions and are feasible candidates for experimental synthesis. Our findings highlight the formation of stable semiconducting 1D NCs of Ti-pentachalcogenides from their 2D counterparts.
  • Article
    Design of Sulfur Resistant Cobalt Catalysts by Boron Promotion: Atomic Scale Insights
    (Sakarya University, 2024) Kızılkaya, A.C.
    The effect of boron promotion on atomic sulfur formation by hydrogen sulfide dissociation on Co(111), flat surfaces of cobalt nanoparticles, was investigated using Density Functional Theory calculations. The results show that on clean Co(111), hydrogen sulfide dissociation proceeds fast due to low activation barriers, yielding atomic sulfur on the cobalt surfaces. Boron promotion hinders the dissociation of hydrogen sulfide due to increased activation barriers. Furthermore, boron prevents the interaction of sulfur compounds with cobalt surface atoms, as these poisons bind on boron. The findings indicate that boron is an effective promoter that can be used to design sulfur resistant cobalt catalysts. © 2024, Sakarya University. All rights reserved.
  • Article
    Novel Single Layers of Holey Crystalline Strcutures of Hf8s12 With Diverse Magnetic States
    (Elsevier, 2025) Kutlu, Tayfun; Ercem, Onur; Yagmurcukardes, Mehmet; Sahin, Hasan
    Motivated by recent experiments revealing the synthesizability of novel M 8 X 12 (where M=transition metal and X=S, Se, or Te) type holey structure transition metal chalcogenide crystals such as W8Se12, the structural, electronic and vibrational properties of the single layer Hf8S12 are investigated. Density functional theory (DFT) based total energy optimizations and dynamic stability analysis show that hafnium disulfide crystals with the known 1T phase are stabilized in the holey crystal structure represented by the chemical formula Hf8S12. While 1T-HfS2 crystals are nonmagnetic, holey Hf8S12 material exhibits 4 different magnetic states along with the ferromagnetic ground state. All these magnetic states display indirect or quasi-indirect narrow bandgap semiconducting behavior. Moreover, it is shown that the in-plane stiffness and Poisson ratio values of each possible magnetic phase of Hf8S12 has a distinctive angle dependency against applied strain. Its stable crystal structure and the magnetic diversity show that Hf8S12 can bean important candidate for magneto-mechanical applications.
  • Article
    Design of Sulfur Resistant Cobalt Catalysts by Boron Promotion: Atomic Scale Insights
    (Sakarya University, 2024) Kizilkaya, A.C.
    The effect of boron promotion on atomic sulfur formation by hydrogen sulfide dissociation on Co(111), flat surfaces of cobalt nanoparticles, was investigated using Density Functional Theory calculations. The results show that on clean Co(111), hydrogen sulfide dissociation proceeds fast due to low activation barriers, yielding atomic sulfur on the cobalt surfaces. Boron promotion hinders the dissociation of hydrogen sulfide due to increased activation barriers. Furthermore, boron prevents the interaction of sulfur compounds with cobalt surface atoms, as these poisons bind on boron. The findings indicate that boron is an effective promoter that can be used to design sulfur resistant cobalt catalysts. © 2024, Sakarya University. All rights reserved.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Synthesis of Acetonitrile From Nh<sub>3</Sub> Mixtures on Molybdenum Nitride: Insights Into the Reaction Mechanism
    (Elsevier, 2024) Kizilkaya, Ali Can; Martinez-Monje, Maria Elena; Prieto, Gonzalo
    Owing to their metallic-like surface electronic properties and their capacity to act as reservoirs and solid transfer agents for active nitrogen, transition metal nitrides are interesting as solid catalysts for C-C and C-N coupling reactions for the bottom-up production of higher (C2+) nitrogenated chemicals from unconventional carbon resources. The catalytically active state and reaction mechanism for the direct synthesis of acetonitrile from syngas/ammonia mixtures are studied on an unsupported Mo catalyst from complementary experimental and computational approaches. Temperature resolved X-ray diffraction and X-ray photoemission spectroscopy verify that an oxidic MoO(3 )catalyst precursor undergoes in situ (near-surface) nitridation, upon exposure to reaction conditions at 723 K, rendering Mo2N the actual working catalyst. Density Functional Theory mechanistic investigations on a gamma- Mo 2 N(100) model surface point to a hydrogen-assisted CO dissociation on the nitride surface. Moreover, surface oxygen, evolved from CO dissociation, is predicted to play a central role as hydrogen acceptor, to enable the dehydrogenative NH3 dissociation. Direct condensation of CH and N adspecies proceeds with a low energy barrier of 33 kJ mol(-1), which makes C-N coupling preferred over full hydrogenation of CHx species, in agreement with the experimental modest selectivity to methane (ca. 10 %). Both experimental and computational results indicate that HCN is a major intermediate product along the reaction pathway to acetonitrile. No energetically feasible associative reaction pathways could be identified for C-C coupling from HCN. The dissociation of the latter intermediate product is predicted to precede the reaction of CN adspecies to CHx. Similarly to NH3 dissociation, dehydrogenative HCN activation on the Mo2N 2 N surface is predicted to be facilitated through hydrogen abstraction by surface oxygen species, yet subjected to a comparatively higher energy barrier (>120 kJ mol(-1)), therefore likely to control the overall kinetics. These findings suggest that the enhancement of HCN dissociation is a central design objective towards Mo2N-based 2 N-based catalysts with advanced performance.