| 1. |
- Chowdhury, Suman, et al.
(författare)
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A real-space study of random extended defects in solids : Application to disordered Stone–Wales defects in graphene
- 2014
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 61:0, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- Abstract We propose here a first-principles, parameter free, real space method for the study of disordered extended defects in solids. We shall illustrate the power of the technique with an application to graphene sheets with randomly placed Stone–Wales defects and shall examine the signature of such random defects on the density of states as a function of their concentration. The technique is general enough to be applied to a whole class of systems with lattice translational symmetry broken not only locally but by extended defects and defect clusters. The real space approach will allow us to distinguish signatures of specific defects and defect clusters.
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| 2. |
- Ganguly, Shreemoyee, et al.
(författare)
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Magnetism in small bimetallic Mn-Co clusters
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:1, s. 014402-
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Tidskriftsartikel (refereegranskat)abstract
- Effects of alloying on the electronic and magnetic properties of MnxCoy (x+y=n=2-5, x=0-n) and Mn2Co11 nanoalloy clusters are investigated using the density-functional theory. Unlike the bulk alloy, the Co-rich clusters are found to be ferromagnetic and the magnetic moment increases with Mn concentration and is larger than the moment of pure Co-n clusters of same size. For a particular sized cluster the magnetic moment increases by 2 mu(B)/Mn-substitution, which is found to be independent of the size and composition. All these results are in good agreement with recent Stern-Gerlach experiments [Phys. Rev. B 75, 014401 (2007) and Phys. Rev. Lett. 98, 113401 (2007)]. Likewise in bulk MnxCo1-x alloy, the local Co moment decreases with increasing Mn concentration.
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| 3. |
- Ganguly, Shreemoyee, et al.
(författare)
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Manipulating magnetism of MnO nano-clusters by tuning the stoichiometry and charge state
- 2015
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 27:5, s. 056002-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we have studied the composition dependent evolution of geometric and magnetic structures of MnO clusters within density functional theory. The magnetic structures are determined by the competition between direct and superexchange interactions, which have been analyzed by the parameters obtained from maximally localized Wannier functions. The intrinsic electronic structures of the clusters have been thoroughly studied by looking into the hybridization (quantified using the Hybridization Index) and charge transfer scenario. Further, the importance of electron correlation in describing simple Mn-dimer and MnO clusters has been discussed within the Hubbard model and hybrid exchange-correlation functional. Our calculated vertical detachment energies of off-stoichiometric MnO clusters compare well with the recent experimental results. Interestingly, the charged state of the cluster strongly influences the geometry and the magnetic structure of the cluster, which are very different from the corresponding neutral counterpart. We have demonstrated that the exchange interaction between Mn atoms can be switched between ferromagnetic and anitiferromagnetic ones by changing the charge state and hence can be useful for spin-based information technology.
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| 4. |
- Ganguly, Shreemoyee, et al.
(författare)
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Unusual structure and magnetism in manganese oxide nanoclusters
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:2, s. 020411-
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Tidskriftsartikel (refereegranskat)abstract
- We report an unusual evolution of structure and magnetism in stoichiometric MnO clusters based on an extensive and unbiased search through the potential-energy surface within density functional theory. The smaller clusters, containing up to five MnO units, adopt two-dimensional structures; and regardless of the size of the cluster, magnetic coupling is found to be antiferromagnetic in contrast to previous theoretical findings. Predicted structure and magnetism are strikingly different from the magnetic core of Mn-based molecular magnets, whereas, they were previously argued to be similar. Both of these features are explained through the inherent electronic structures of the clusters.
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| 5. |
- Iusan, Diana, et al.
(författare)
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Microscopic picture of Co clustering in ZnO
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : The American Physical Society. - 1098-0121 .- 1550-235X. ; 79:12, s. 125202-
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory was applied to study the chemical and magnetic interactions between Co atoms doped in ZnO. It was found that the Co impurities tend to form nanoclusters and the interactions between these atoms are antiferromagnetic within the local spin-density approximation (LSDA)+Hubbard U approach. The extracted interatomic exchange parameters agree reasonably well with recent experimental results. We have analyzed and compared the electronic structure obtained using the LSDA and LSDA+U approaches and found that the LSDA+U gives the most reasonable result, highlighting the importance of short-ranged antiferromagnetic interactions due to superexchange.
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| 6. |
- Samanta, Sudipta, et al.
(författare)
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Twist-dependent stacking energy of base-pair steps in B-DNA geometry : A density functional theory approach
- 2008
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 108:6, s. 1173-1180
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Tidskriftsartikel (refereegranskat)abstract
- Stacking energy of all the 10 unique DNA base-pair steps (bp step) are calculated using density functional theory within the ultrasoft pseudopotential plane wave method and local density approximation for the exchange-correlation functional. We have studied the dependence of stacking energy on twist angle, an aspect found difficult to explain using classical theory. We have found that the twist angle for different bp steps at stacking energy minimum matches extremely well with the values of average twist obtained from B-DNA crystal structure data. This indicates that the use of a proper quantum chemical method to calculate the pi-pi electronic interactions may explain stacking energy without incorporating hydrophobic interaction through solvent or effect of backbone through pseudobond. From the twist angle-dependent stacking energy profile, we have also generated the probability distributions of twist for all the bp steps and calculated the variance of the distribution. Our calculated variances show similar trend to that of the experimental data for which sufficient numbers of data are available. The TA, AT, and CG doublets show large variances among the 10 possible bp steps, indicating their maximum flexibility. This might be the case of unusual deformation observed at the TATA-box while binding to TBP protein.
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