Nanoclusters of noble metals stand as original structures, halfway between the molecular and the solid world. Their highly symmetric geometry that differs from the bulk arrangement of their constitutive metal, gives rise to size and metal dependent molecule-like properties. Among those, the most striking one may be the presence of an important electronic gap due to their discrete electronic structure. Lately, the use of these specific « nano-properties  » has rapidly grown and direct applications were successfully achieved in various fields (catalysis, photovoltaics, redox) especially for gold nanoclusters.
Gold nanoclusters have been extensively studied at the theoretical level during the last decade. Nevertheless, such metallic architectures can rapidly grow in size, reaching dimensions of several nanometers and embedding thousands of electrons. When describing such large systems a quantum fashion, typically within Density Functional Theory (DFT), one rapidly faces computation bottlenecks (memory, CPU time). In this context, we present the parameterization of a low calculation cost « Density Functional Tight-Binding  » (DFTB) method which allows to study nanoclusters of several hundreds of gold atoms, and coated with a shell of organic ligands. After a description and a validation of this DFTB method applied to gold-organic systems,[1] we will focus on rationalizing and predicting the electronic and optical properties of nanoclusters of different sizes and shapes, as well as functionalized with photoactive molecules (fluorophore, photochrome).[2] In fact, such hybrid system where the gold nanocluster interacts with an anchored molecule bearing a light-driven function paves the way towards smart building blocks for optoelectronic nanodevices,[3] and the ability to model such system at a reasonable computational cost is crucial to fasten their design.
[1] Fihey A., Hettich C., Touzeau J., Maurel F., Perrier A., Köhler C., Aradi B., Frauenheim T., J. Comput. Chem., 36, 2075-2087 (2015)
[2] Fihey A., Maurel F., Perrier A., J. Phys. Chem. C, 118, 4444-4453 (2014)
[3] Fihey A., Maurel F., Perrier A., Phys. Chem. Chem. Phys., 16, 26240-26251 (2014)
