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Unformatted text preview: Electronic properties of CdSe nanocrystals in the absence and presence of a dielectric medium Eran Rabani, Bala ´ zs Hete ´ nyi, and B. J. Berne Department of Chemistry and Center for Biomolecular Simulation, Columbia University, 3000 Broadway, New York, New York 10027 L. E. Brus Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027 ~ Received 16 October 1998; accepted 8 December 1998 ! We present a detailed study of the electronic properties of CdSe nanocrystals in the absence and presence of a dielectric medium. The electronic structure of the nanocrystal is modeled within the framework of the empirical pseudopotential method. We use a real-space grid representation of the wave function, and obtain the eigenvalues and eigenstates of the one-electron Hamiltonian using a slightly modified version of the filter-diagonalization method. The band gap, density of states, charge density, multipole moments, and electronic polarizabilities are studied in detail for an isolated nanocrystal. We discuss the implications of the results for the long range electrostatic and dispersion interactions between two CdSe nanocrystals. To study the effects of the surroundings we develop a self-consistent reaction field method consistent with the empirical pseudopotential method. We use the eigenstates of the isolated nanocrystal and iterate the self-consistent equations until converged results are obtained. The results show that the electronic properties of polar CdSe nanocrystals are quite sensitive to the environment. © 1999 American Institute of Physics. @ S0021-9606 ~ 99 ! 70910-4 # I. INTRODUCTION The interest in semiconductors which are spatially con- fined to a few tens of nanometers, and which contain hun- dreds of atoms, has increased in recent years. 1–9 The devel- opment of experimental methods along with improvements in epitaxial growth techniques, 10–13 has made it possible to study various electronic properties of semiconductor nano- crystals in great detail. In particular colloidally prepared CdSe nanocrystals have received much of the experimental attention. 10,11,14–26 The experimental interest in CdSe nano- crystals has raised a number of questions that require the use of electronic structure theory for a complete explanation. Ex- act electronic structure calculations of CdSe nanocrystals are extremely difficult in view of the large number of atoms and electrons involved, 27 and the lack of periodicity. Therefore, several approximate theoretical methods and models have been developed in the last few years. The simplest approach is based on the effective mass approximation, 28–31 which can be extended to incorporate multiband couplings, 32 i.e., band mixing induced by the effect of finite size....
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This note was uploaded on 09/30/2010 for the course MAN. ENG. isl taught by Professor M.e. during the Spring '09 term at Istanbul Technical University.
- Spring '09