(FLUIDOS2012: Abstract Format: a maximum of 500 words)
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Numerical modeling studies offer important opportunities that could potentially lead to
new discoveries in nanoscience, complementing and guiding experiments. In spite of this
potential, limitations in the efficiency as well as the reliability of the most popular numerical
methodologies available in the literature still persist. On the one hand, the ability and
reliability of first principle methods in describing nanomaterial properties is shadowed by the
prohibitive computational time involved in the calculation of the typical Hamiltonian matrix
elements and the matrix diagonalizations. On the other hand, computationally efficient
empirical calculations based on classical force fields are not reliable because they fail to
describe quantum effects that are expected to be important at the nanoscale[1]. It is in this
context that the Tight-Binding (TB) approximation offers a promising technique for
nanomaterial modeling.In this work we propose a perturbative correction to the tight-binding
total energy expression that depends on the fluctuation of the electron density of the system
with respect to a reference atomic density. Our results lead to the conclusion that taking into
account the intratomic interactions in TB is crucial in recovering the ground state structure as
well the turnover from planar-to-nonplanar configuration of gold clusters, as predicted by
Density Functional Theory (DFT) calculations. In the procedure proposed in this work, this is
achieved without the necessity of the cumbersome, computationally expensive and arbitrary
inclusion of the electronic structure data of small clusters (obtained from first principle
calculations) when parametrizing the Tight-Binding hamiltonian, as has been done elsewhere
for some metal nanoclusters. The results in Fig. 1 show that the uncorrected NRL-TB
hamiltonian predicts smaller equilibrium distances and larger binding energy when compared
to DFT calculations, while the perturbatively corrected version of the same TB hamiltonian
substantially corrects these differences, a fact that elucidates the importance of taking into
account the orbital popula- tion fluctuations in the TB total energy calculation. The results in
Fig. 1 show that the uncorrected NRL-TB hamiltonian predicts smaller equilibrium distances
and larger binding energy when compared to DFT calculations, while the perturbatively
corrected version of the same TB hamiltonian substantially corrects these differences, a fact
that elucidates the importance of taking into account the orbital population fluctuations in the
TB total energy calculation. In conclusion, the above results show that inclusion of the on-site
orbital population fluctuation in the total energy allow to recover relevant properties of gold
nanoclusters, where other TB parameterizations and classical empirical potentials fail, despite
the explicit inclusion of the structures of some discrete clusters in the parameterization of
these methods. The robustness and relatively small computational cost -as compared with
more accurate ab initio and DFT methodologies- make our TB model a computationally
efficient tool to combine with Molecular Dynamics and/or Monte Carlo calculations, to
determine and predict reliable thermochemical and physical properties of nanomaterials. The
perturbatively corrected TB model introduced in this work is particularly