Surface relaxation in CdSe nanocrystals

Abstract

Total energy minimization is applied to semiempirical tight-binding CdSe nanocrystal models with diameter up to 31 Å. The crystallites have wurtzite lattice structure and ligand-terminated surfaces. It is found that the qualitative features of the surface relaxation in nanocrystals and at bulk surfaces are similar. When surface relaxation is incorporated, the onsets of absorption are determined by interior-to-interior transitions with little contribution from surface-localized states. The fine structure and exchange splittings derived from these clusters are in good agreement with experimental measurements. The effects of ligand parametrization, surface atom composition, and the contribution of surface states to the exciton fine structure are analyzed.

Size dependence of nanostructures: Impact of bond order deficiency

“…Theoretically, nanoparticles have bulk-like interior structure [180] with surface relaxation [163,181] in a manner comparable to that of bulk surfaces. However, classical and quantum MD simulations have suggested that disorder may pervade throughout nanoparticles [182,183].…”

Ab initiocalculations of the structural and electronic properties ofHgmTenclusters

“…[3][4][5][6][7][8][9] Meanwhile, there have been a number of theoretical studies devoted to the structural, electronic, and optical properties of these QDs and the smaller bare clusters. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] In much previous theoretical work, the effective mass method has been applied to investigate the size-dependent electronic properties of the larger QDs, in which the underlying structure is less important. [25][26][27][28][29] Alternatively, semiempirical tight-binding methods have been used to get more detailed structural and electronic information of QDs up to 31 Å diameter.…”

“…[25][26][27][28][29] Alternatively, semiempirical tight-binding methods have been used to get more detailed structural and electronic information of QDs up to 31 Å diameter. 15,[18][19][20][21][22] Also the atomistic pseudopotential approach has been applied to study the quasiparticle gap 23 and the excitonic transitions 24 of QDs. However, there have been much fewer first principles studies due to the computational demands.…”

Tight-binding model for semiconductor nanostructures

“…Simple model studies based on the effective mass approximation 15,22 or a multi-band k · pmodel 23,24,25 describe the QD by a confinement potential caused by the band offsets, for instance; they give qualitative insights into the formation of bound (hole and electron) states, but they are too crude for quantitative, material specific results or predictions. More suitable for a microscopic description are empirical pseudopotential methods 26,27,28,29 as well as empirical tight-binding models 30,31,32,33,34,35,36,37,38,39,40,41 . The empirical pseudopotential methods allow for a detailed variation of the wave functions on the atomic scale.…”