Bio Chem Press  Internet Electronic Journal of Molecular Design is a refereed journal for scientific papers regarding all applications of molecular design
Home | News | Current Issue | Journal Index | IECMD 2004 | Preprint Index | Instructions for Authors | Send the Manuscript | Special Issue
 BioChemPress.com  To bookmark this site press Ctrl D
 
   Home
   News & Announcements
  Journal Info
   Current Issue
   Journal Index
   Preprint Index
   Editor
   Advisory Board
  Conference Info
   IECMD 2004
   Day 1
   Day 2
   Day 3
   Day 4
   Day 5
   Day 6
   Day 7
   Day 8
   Day 9
   Day 10
   IECMD 2003
  BioChem Links
   CoEPrA
   Support Vector Machines
  Author Info
   Instructions for Authors
   Send the Manuscript
   Special Issue
  Contact
   Editorial Office
   Subscription
   Advertising
   Copyright
  User Info
   Terms of Use
   License

Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
ABSTRACT - Internet Electron. J. Mol. Des. May 2005, Volume 4, Number 5, 316-328

Computational Studies of 1T and 2H TaS2 in Crystalline and Nanotubular Forms: Structural and Electronic Properties
Andrew N. Enyashin, Igor R. Shein, Nadezhda I. Medvedeva, and Alexander L. Ivanovskii
Internet Electron. J. Mol. Des. 2005, 4, 316-328

Free: Download the paper in PDF format Return to Table of Contents Get Acrobat Reader to view and print the paper

Abstract:
Since the discovery of carbon nanotubes in 1991, inorganic nanotubes (NTs) have received much attention. The layered chalcogenides, having structures analogous to graphite, are known to be unstable toward bending and show high propensity to form curved structures. Recently, apart from carbon nanotubes, nanotubes of the layered d-metal disulfides (MS2, M = Mo, W, Nb, Ta, Ti, Zr) have been synthesized. However the information on the structural and electronic properties of curved nanostructures based on tantalum disulfide is lacking to date. On the other hand, the study of TaS2 bulk materials has been actively pursued during the last years owing their interesting properties and potential applications. One of the most important and intriguing problem that attracts the attention of researchers is the modification of properties of inorganic systems going from bulk to nanoscale state. In the present paper the electronic band structure of 1T and 2H polytypes of layered tantalum disulfide in crystalline and nanotubular forms has been studied by means of band structure approaches. For the first time we discuss the changes in electronic properties of TaS2 nanotubes depending from the atomic arrangement in tube walls (octahedral or trigonal prismatic) and from the tube diameters and geometry (zigzag or armchair-like). The electronic band structures, densities of states, electron density maps, bonding indices - crystal orbital overlap populations and total band energies of 1T and 2H polytypes of TaS2 bulk and nanotubes have been obtained using the ab initio full-potential linear muffin tin orbitals (FPLMTO) and the semi-empirical tight-binding EHT band structure approaches. The energy bands for 1T and 2H polytypes of crystalline TaS2 are obtained; using of the total energy calculations, we found that there is a gain in energy of 0.231 eV/formula unit for 2H structure, reflecting the fact that the ideal 1T phase is unstable at low temperatures. The DOS at the Fermi energy N(EF) is controlled by the overlap between the S p and Ta d states. This overlap results in a metallic state for TaS2. The DOS curves of 2H and 1T polytypes obtained by the semi-empirical EHT calculations are in reasonable agreement with ab initio FLMTO data. The atomic models of 1T and 2H TaS2 nanotubes have been constructed. The electronic structure and bond indices of nanotubes have been calculated and analyzed as a function of the tubes diameters (D) in the armchair- and zigzag-like forms. Within the range of diameters examined, the zigzag configurations of 1T and 2H like tubes appear to be the most stable than armchair configurations. All NTs are metallic-like and their electronic spectra are similar to the DOS of the corresponding planar layers. The Fermi level is located in the region of the non-bonding Ta d band. For the armchair-like 2H TaS2 NTs there is a pronounced DOS peak at the Fermi level. Since the this sharp DOS peak for such NTs is half-filled with high N(EF), one would expect that the some 2H TaS2 NTs may be superconducting, as it has been obtained recently for NbSe2 nanotubes (2003). The electronic properties and chemical bonding of 2H and 1T polytypes of layered tantalum disulfide in crystalline and nanotubular forms have been studied with the ab initio FPLMTO and the semi-empirical tight-binding EHT approaches. We show that both zigzag- and armchair-like nanotubes are metallic-like, and the tube stability trends to vanish for very small NT diameters. Zigzag-like nanotubes were found to be more stable. It was established that Ta-S covalent bonds are the strongest interactions in TaS2 bulk and NTs, whereas Ta-Ta bonds are much weaker.

Free: Download the paper in PDF format Return to Table of Contents Get Acrobat Reader to view and print the paper

Home | News | Current Issue | Journal Index | IECMD 2004 | Preprint Index | Instructions for Authors | Send the Manuscript | Special Issue
Last changes: January 5, 2006 Webmaster
http://www.biochempress.com/
Copyright © 2001-2006 Ovidiu Ivanciuc