**Optical Properties of Gold Nanoclusters Functionalized with a Small
Organic Compound: Modeling by an Integrated Quantum-Classical Approach**

X Li and V Carravetta and C Li and S Monti and Z Rinkevicius and H Aring;gren, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 12, 3325-3339 (2016).

DOI: 10.1021/acs.jctc.6b00283

Motivated by the growing importance of organometallic nanostructured
materials and nanoparticles as microscopic devices for diagnostic and
sensing applications, and by the recent considerable development in the
simulation of such materials, we here choose a prototype system para-
nitroaniline (pNA) on gold nanoparticles to demonstrate effective
strategies for designing metal nanoparticles with organic conjugates
from fundamental principles. We investigated the motion, adsorption
mode, and physical chemistry properties of gold-pNA particles,
increasing in size, through classical molecular dynamics (MD)
simulations in connection with quantum chemistry (QC) calculations. We
apply the quantum mechanics-capacitance molecular mechanics method **Z.
Rinkevicius et al. J. Chem. Theory Comput. 2014, 10, 989** for
calculations of the properties of the conjugate nanoparticles, where
time dependent density functional theory is used for the QM part and a
capacitance-polarizability parametrization of the MM part, where induced
dipoles and charges by metallic charge transfer are considered.
Dispersion and short-range repulsion forces are included as well. The
scheme is applied to one- and two-photon absorption of gold-pNA clusters
increasing in size toward the nanometer scale. Charge imaging of the
surface introduces red-shifts both because of altered excitation energy
dependence and variation of the relative intensity of the inherent
states making up for the total band profile. For the smaller
nanoparticles the difference in the crystal facets are important for the
spectral outcome which is also influenced by the surrounding MM
environment.

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