A polarizable coarse-grained model for metal, metal oxide and composite metal/metal oxide nanoparticles and its applications.

We present a selected set of exemplifying applications of the novel polarizable coarse-grained model [see the first part] to various outstanding problems in the physics and chemistry of nanoparticles: electrostatic potential around silver and gold nanoparticles; spontaneous and external electric field-driven self-organization of gold and silver nanoparticle systems; and physisorption of carbon dioxide on titanium dioxide nanoparticles decorated with a gold catalyst. In the first application, the developed model has shown capabilities of predicting long-range potential with accuracy comparable to the tight-binding density functional theory methods. Furthermore, the electrostatic potential analysis in hot spot regions allowed us to identify twin defect lines in a silver nanostar as a promising candidate for an enhancer in surface-enhanced Raman spectroscopy. In the second application, the developed model has facilitated the elucidation of the microscopic mechanisms responsible for the self-organization of gold and silver nanoparticles. Analysis of Monte-Carlo simulations established that the self-organization process is driven by van der Waals interactions in the absence of an external electric field, and that it becomes gradually driven by electrostatic interactions in the presence of an external electric field with increasing strength of the external electric field. In the third application, the developed model combined with Monte-Carlo simulations has identified the dominant mechanism responsible for carbon dioxide transfer to the catalytic sites. Analysis of the obtained results indicates that surface diffusion is the dominant mechanism for the transport of carbon dioxide to the catalytic sites, and only in exceptional situations, direct physisorption becomes a competitive mechanism with the surface diffusion mechanism. These successful applications of the developed model indicate its wide range of applicability to various problems in the chemistry and physics of nanoparticles.

A polarizable coarse-grained model for metal, metal oxide and composite metal/metal oxide nanoparticles: development and implementation.

We present a polarizable coarse-grained model for metal, metal oxide, and composite metal/metal oxide nanoparticles with well-defined crystalline surfaces. The developed model uses a low-resolution polarizable "surface beads" representation of the nanoparticle's geometry and pairwise cross nanoparticle potential consisting of van der Waals and electrostatic interaction terms. The electrostatic interaction term of the cross nanoparticle potential incorporates a crucial physical aspect of electrostatic interaction into the metal and metal oxide systems, such as induced surface charges, making it possible to explore the nanoparticles' behavior in complex environments as well as investigate the interplay between electrostatic and van der Waals interactions in nanoparticle systems. The iterative stability, computational scaling, and performance of the presented model was tested on selected systems of gold, titanium dioxide, and composite gold/titanium dioxide nanoparticle systems. The model exhibits robust iterative stability and is able to converge the charge equilibration equation for fluctuating induced charges and dipoles within 10-60 "tug-tow" iterations in challenging situations, like crowded nanoparticle systems or nanoparticle systems in extreme external electric fields. The computation scaling of the presented model is semi-linear with respect to the number of nanoparticles in the system. It slightly varies depending on the size distribution of nanoparticles in a specific nanoparticle system. The computation cost of the model is significantly lower than that of conventional atomistic polarizable force field models and enables the treatment of large nanoparticle systems that are beyond the reach of currently existing atomistic force field models.

Antibacterial Activity of Silver and Gold Particles Formed on Titania Thin Films.

Metal-based nanoparticles with antimicrobial activity are gaining a lot of attention in recent years due to the increased antibiotics resistance. The development and the pathogenesis of oral diseases are usually associated with the formation of bacteria biofilms on the surfaces; therefore, it is crucial to investigate the materials and their properties that would reduce bacterial attachment and biofilm formation. This work provides a systematic investigation of the physical-chemical properties and the antibacterial activity of TiO2 thin films decorated by Ag and Au nanoparticles (NP) against Veillonella parvula and Neisseria sicca species associated with oral diseases. TiO2 thin films were formed using reactive magnetron sputtering by obtaining as-deposited amorphous and crystalline TiO2 thin films after annealing. Au and Ag NP were formed using a two-step process: magnetron sputtering of thin metal films and solid-state dewetting. The surface properties and crystallographic nature of TiO2/NP structures were investigated by SEM, XPS, XRD, and optical microscopy. It was found that the higher thickness of Au and Ag thin films results in the formation of the enlarged NPs and increased distance between them, influencing the antibacterial activity of the formed structures. TiO2 surface with AgNP exhibited higher antibacterial efficiency than Au nanostructured titania surfaces and effectively reduced the concentration of the bacteria. The process of the observation and identification of the presence of bacteria using the deep learning technique was realized.