Malzeme Bilimi ve Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/396

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Citation - WoS: 31
Citation - Scopus: 30
Ionization Energies, Coulomb Explosion, Fragmentation, Geometric, and Electronic Structures of Multicharged Boron Clusters Bn (n=2-13)
(Amer Physical Soc, 2011) Tas, Murat; Ozdogan, Cem; Boustani, Ihsan; Akman, Nurten
Based on the ab initio quantum chemical methods, we have determined fragmentation channels, ionization energies, and the Coulomb explosion of multicharged boron clusters B-n (n = 2-13), where n is the cluster size. The electron-deficient boron clusters sustain more stability and hardly fragment when they are negatively charged. Stability of boron clusters decreases with increasing ionization. Only by the first ionization the odd-size clusters are more stable than the even-size clusters. Further ionizations cause the repulsive Coulomb force between the constituent atoms to get stronger, and lead first to metastable states, then to the Coulomb explosion of clusters. None of the cationic boron clusters studied remain stable after six times ionization. The critical charge for metastability is estimated as Q(m) <= n/2 for even-size clusters, and Q(m) <= 1/2 (n - 1) for odd-size clusters. In addition, the critical charge for the Coulomb explosion is found to be Q(c) = n/2 + 1 for even-size clusters, and Q(c) = 1/2(n + 1) for odd-size clusters. Relative stability of clusters with respect to their nearest neighbors is determined from the analysis of their second energy difference data. Several dissociation channels of B-n(+) and B-13(Q) isomers with the lowest fragmentation energies are presented. All of the vibrational frequencies are found positive indicating that no transition state is possible for the clusters studied. Reliability of our data is verified with a good agreement with experimental results.
Citation - WoS: 209
Citation - Scopus: 218
Stability of Edge States and Edge Magnetism in Graphene Nanoribbons
(Amer Physical Soc, 2011) Ozdogan, Cem; Quandt, Alexander; Fehske, Holger; Kunstmann, Jens
We critically discuss the stability of edge states and edge magnetism in zigzag edge graphene nanoribbons (ZGNRs). We point out that magnetic edge states might not exist in real systems and show that there are at least three very natural mechanisms-edge reconstruction, edge passivation, and edge closure-which dramatically reduce the effect of edge states in ZGNRs or even totally eliminate them. Even if systems with magnetic edge states could be made, the intrinsic magnetism would not be stable at room temperature. Charge doping and the presence of edge defects further destabilize the intrinsic magnetism of such systems.

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