BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//CERN//INDICO//EN
BEGIN:VEVENT
SUMMARY:Computational approaches for electronic properties of semiconducti
 ng materials and nanostructures
DTSTART;VALUE=DATE-TIME:20121018T101500Z
DTEND;VALUE=DATE-TIME:20121018T104500Z
DTSTAMP;VALUE=DATE-TIME:20261011T041928Z
UID:indico-contribution-167@indico.ipb.ac.rs
DESCRIPTION:Speakers: Nenad Vukmirovic (Scientific Computing Laboratory\, 
 Institute of Physics Belgrade\, University of Belgrade)\nDensity functiona
 l theory (DFT) provides a reliable theoretical framework for studying the 
 electronic properties of atoms\, molecules\, bulk materials\, surfaces\, i
 nterfaces\, etc. However\, due to its computational effort\, the calculati
 ons based on DFT are typically performed only for relatively small molecul
 es or for crystalline materials where periodicity of the structure can be 
 exploited. There is a wealth of highly relevant systems which are currentl
 y beyond the reach of standard DFT calculations\, such as\, for example\, 
 disordered conjugated polymers\, inorganic nanocrystals\, and polycrystall
 ine materials. To study these systems\, one typically needs to do the calc
 ulation for a supercell containing thousands of atoms to get reliable info
 rmation about the properties of the system.\n\nThe methods that can be use
 d to study even such systems will be presented and computational aspects o
 f the applications of these methods will be discussed. \n\nCharge patching
  method (CPM) [1] is the method for the construction of electronic charge 
 density of the system that avoids demanding self-consistent DFT calculatio
 ns. It is based on the idea that electronic charge density in the neighbor
 hood of an atom depends mainly on its local environment. Such an assumptio
 n is typically valid in semiconducting and insulating materials without an
 y long-range charge transfer. The contribution of each atom to electronic 
 charge density of the system is therefore extracted from the calculation o
 f some small prototype system where atoms have the same environment as in 
 the large system under study. Electronic charge density of the large syste
 m is then simply obtained by adding the contributions of each atom. With e
 lectronic charge density at hand\, one gets the single-particle Hamiltonia
 n by solving the Poisson equation for the Hartree potential and using the 
 local density approximation formula for the exchange-correlation potential
 .\n\nTo study the electrical properties of the material\, one does not nee
 d to calculate all the electronic states of the Hamiltonian but only these
  in the region near the band gap. Overlapping fragments method (OFM) [2] w
 as developed to efficiently find these states. The method is in particular
  suited to study disordered conjugated polymers [3]. It is based on the di
 vison of the system into fragments and the representation of the Hamiltoni
 an in the basis of molecular orbitals of these fragments. It is typically 
 sufficient to use only a few molecular orbitals of each fragment. This app
 roach strongly reduces the size of the Hamiltonian  matrix that needs to b
 e diagonalized down to the size of several hundreds.\n\nFinally\, several 
 applications of these methods in the studies of organic solar cell materia
 ls will be briefly presented.\n\n[1] N. Vukmirovic and L.-W. Wang\, J. Che
 m. Phys. 128\, 121102 (2008).\n[2] N. Vukmirovic and L.-W. Wang\, J. Chem.
  Phys. 134\, 094119 (2011).\n[3] N. Vukmirovic and L.-W. Wang\, J. Phys. C
 hem. B 115\, 1792 (2011).\n\nhttps://events.saifa.rs/event/291/contributio
 ns/167/
LOCATION:National Library of Serbia
URL:https://events.saifa.rs/event/291/contributions/167/
END:VEVENT
END:VCALENDAR