Structural and Electronic Properties of Zno nanoclusters: a b3lyp dft study

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Structural and Electronic Properties of ZnO NANOCLUSTERs: A B3LYP 
DFT Study 
D. K. Pandey 
a
, P. S. Yadav, S. Agrawal and B. K. Agrawal
Department of Physics, University of Allahabad, Allahabad, India 
a
Email: [e-mail] 
Keywords: Nanoclusters, Electronic properties, Zero-point energy, Dipole moments, DFT study. 
Abstract. An ab initio B3LYP-DFT/6-311G(3df) study has been performed for the stability, 
structural and electronic properties of forty Zn
m
O
n
(m + n = p = 2 to 4) nanoclusters. We also 
consider the zero point energy correction. The nanoclusters containing large number of strongly 
electronegative O atoms for p = 3 and 4 are found to be most stable as compared to the other 
nanoclusters of the same configuration. The most stable clusters have linear or planer structures and 
not the three dimensional ones. The observed trend of decrease of the HOMO-LUMO gap with the 
size of the nanocluster is in conformity with the quantum confined behavior. 
Introduction
Nanostructures of semiconducting materials have drawn attention for their paramount technological 
potential. A nanocluster is an intermediate phase between the molecule and bulk, whose electronic 
and other properties may be exotic. In nanoclusters, the surface area to volume ratio is quite high.
Among II-VI semiconductors, Zinc oxide (ZnO) has special importance because of its wide range 
of applications [1-3]. ZnO nanomaterials have biomedical application also for their bio-safety and 
biocompatibility. Bulk ZnO exhibits near ultraviolet emission and transparent conductivity, owning 
to its direct band gap of 3.37 eV and large exciton binding energy (60 meV). The noncentral 
symmetry seen in ZnO makes it piezoelectric and a promising multifunctional material.
Many workers have reported the stability of small zinc oxide nanoclusters by using a time of 
flight mass spectrometry initiated by laser ablation of solid zinc oxide [4-6]. Various experimental 
techniques have been employed to synthesize the ZnO nanomaterials [7-12]. Wu et al. [13] have 
prepared small (ZnO)
n
, n = 1-15, nanoclusters having sizes laying in the range of 3-10 Å using the 
electroporation of unilamellar vesicles. The growth of the nanoclusters was associated with novel 
alternating, red and blue shifts of the absorption edge. They compared their data with theoretical 
results [14]. There have been several theoretical studies of the structural stabilities, HOMO-LUMO 
gaps and the optical absorption of some nanoclusters of Zn
i
O
i
type [15-22], but the other physical 
properties like the ionization potential (IP), electron affinity (EA), etc. for all the possible 
configurations have not been reported so far upto the knowledge of the authors. 
Earlier, we have performed an exhaustive ab-initio study of ZnS nanoclusters [23]. We now 
extend our study to the most general Zn
m
O
n
nanoclusters. Here, we report the results of our 
theoretical study of the equilibrium geometries, stabilities, HOMO-LUMO gaps, adiabatic and 
vertical ionization potentials (IP) and electron affinities (EA), charges on atoms and dipole moment 
of small size Zn
m
O
n
(m + n = p = 2 to 4) nanoclusters by using the B3LYP-DFT/6-311G(3df) 
method. 
Method 
For the structural optimization of the ZnO nanoclusters, we have employed the B3LYP-DFT/6-
311G(3df) version in the Gaussian-03 code [24] which employs the hierarchy of procedures 
corresponding to different approximation methods. The harmonic vibrational frequencies are 
determined by analytical differentiation of gradient. A large basis set for each atom is selected for 
the most precise calculation. We use triple split valance basis set, 6-311G which employs three 
Advanced Materials Research Vol. 650 (2013) pp 29-33
Online available since 2013/Jan/25 at 
www.scientific.net
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.650.29
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
www.ttp.net. (ID: 130.15.241.167, Queen's University, Kingston, Canada-29/09/14,10:30:58)

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sizes of the contracted functions per orbital. Contracted functions are the combinations of the 
Gaussian functions. The advantage of the split valance basis set is that it allows the orbitals to 
change their size without making any change in the shape of the orbitals. Also, one uses a 
polarizable basis set 6-311G(3df) by adding orbitals with the angular momentum beyond what is 
necessary for the description of the ground state of each atom.