Download presentation

Presentation is loading. Please wait.

Published byJenna Hoover Modified over 4 years ago

1
A 10-a editie a Seminarului National de nanostiinta si nanotehnologie 18 mai 2011 Biblioteca Academiei Romane Tight-binding (TB) methods: Empirical Tight-binding (ETB) Ab-initio Tight-Binding Capability to render the atomistic nature of phenomena. ETB - describes the electronic structure of complex systems like interfaces, defects in crystals, amorphous materials, nano-clusters, and quantum dots (3 orders of magnitude faster than ab-initio DFT][C. Delerue et al., phys.stat.sol. (b) 227, 115 (2001)]. The parameter-free DFT-TB-LMTO (tight-binding-linear muffin-tin orbitals) method has become more widely used not only for crystals, but also for low-dimensional systems like layered structures [I. Turek et al., Electronic Structure of Disordered Alloy, Surfaces, and Interfaces, Kluwer Academic Publishers 1997]. ETB assumes:(1) an orthogonal basis of states localized around atomic sites; (2) diagonal coordinate operator in this basis (gauge-invariance). Overlap and optical matrix elements : Phys. Rev. B.72, 125105 (2005) 2D Graphene The tight-binding description of highly mismatched semiconductor alloys The developments[i] in the growth of Si lattice-matched BeSe0.41Te0.59 a new class of Si based devices.[i] The gap in size and orbital energies between Se/ Te and large lattice mismatch between BeTe/ BeSe makes the virtual-crystal approximation inappropriate. The band anti-crossing (BAC) model has been introduced in order to explain the electronic structure of highly mismatched alloys like ZnSexTe1-x.[ii] [i] Clark, K. et al., J. Appl. Phys. 88, 7201 (2000); Kirk, W. P. et al., Supperlatt. Microstruct. 28, 377 (2000).[ii] [i] [ii][ii] Walukiewicz, W. et al., Phys. Rev. Lett. 85, 1552 (2000); Wu, J. et al., Phys. Rev. B 68,033206 (2003). Application to sp3s* TB Hamiltonian PRB, 72 073204, 2005. Perturbed GF due to impurity by averaging over impurity configurations. The model is directly applied to sp 3 s* Hamiltonian[+] with spin-orbit interaction.[++][+][++] The TB Hamiltonian is written in the sp 3 hybrid basis and the basis is rotated in such a way that a unit cell is formed by the anion hybrid orbitals and the cation hybrid orbitals pointed toward the anion site. The s* orbitals remain unchanged. [+] Vogl, P. Hjalmarson, H. P. and Dow,J. D. J. Phys. Chem. Solids 44, 365 (1983). [+] [++][++] Chadi, D. J. Phys. Rev. B 16, 790 (1977). Real-Space LMTO Method for Large Systems DFT, ground state theory (LDA, etc); HFA not that good for solids. Exchange-correlation potentials and quasiparticle energies in the GWA or Screened Exchange: 1-particle GF and screened Coulomb interaction in predicting bandgaps (PRL 93 126406 2004). Too demanding! Approximate methods in order to consider correlations- good for large systems (**Solid State Communications 150, 888; 2010). TB-LMTO-ASA PRB 34, 5253, 1986 FAST CALCULATION of the Hamiltonian and GF permits the evaluation of the dielectric permittivity and the use of a dielectric scaling method to estimate the bandgap**. The bangap is improved with respect to DFT. Potential use for large systems! Spin polarization by spin dependent tunneling through an indirect barrier Phys. Rev. B. 73, 075313, 2006: TB PMC-Physics B, 1, 13, 2008: ab-initio Windows of large spin polarization due to Fane resonances in tunneling though an indirect barrier. Atomistic Description of Nanostructures Titus Sandu (titus.sandu@imt.ro) National Institute for R&D in Microtechnologies, Bucharest

Similar presentations

OK

Lectures Introduction to computational modelling and statistics1 Potential models2 Density Functional.

Lectures Introduction to computational modelling and statistics1 Potential models2 Density Functional.

© 2018 SlidePlayer.com Inc.

All rights reserved.

By using this website, you agree with our use of **cookies** to functioning of the site. More info in our Privacy Policy and Google Privacy & Terms.

Ads by Google

Ppt on wildlife and vegetation conservation Ppt on eia report today Ppt on private labels in india Ppt on industrialisation and social change Ppt on c language fundamentals worksheets Ppt on do's and don'ts of group discussion topics Ppt on sea level rise data Ppt on abo blood grouping reagents Ppt on hydraulic free piston engines Ppt on food chains and webs