RESUMO
In recent years, both chitosan and ZnO nanostructures have been identified as potential antibacterial substances; however, the potential applications of chitosan adsorbed on ZnO nanowires have not been explored and could offer exciting new perspectives for both materials, for example, in biocompatible electronic circuits. In this work, we investigate the effect of chitosan on the electronic properties of triangular ZnO nanowires (ZnO NWs) from a theoretical perspective. All calculations were performed using density functional theory within the generalized gradient approximation. We considered six different positions of the chitosan molecule (CS) on the nanowire surface. We varied the amine position of CS, viewing it parallel, perpendicular, and at a 45° angle with respect to the NW axis. Our results show that all configurations are chemically stable; moreover, the interaction of the NW surface with the OH radical of CS creates flat states within the band gap energy of the ZnO NWs that might resemble p-doping. In addition, these states induce changes in the band gap energy of the ZnO NWs. All NWs show high chemical stability regardless of the CS position; hence, the adsorption results of all NW assemblies appear to be chemically favorable.
RESUMO
A necessary first step in the development of technologies such as artificial photosynthesis is understanding the photoexcitation process within the basic building blocks of naturally occurring light harvesting complexes (LHCs). The most important of these building blocks in biological LHCs such as LHC II from green plants are the chlorophyll a (Chl a) and chlorophyll b (Chl b) chromophores dispersed throughout the protein matrix. However, efforts to describe such systems are still hampered by the lack of computationally efficient and accurate methods that are able to describe optical absorption in large biomolecules. In this work, we employ a highly efficient linear combination of atomic orbitals (LCAOs) to represent the Kohn-Sham (KS) wave functions at the density functional theory (DFT) level and perform time-dependent density functional theory (TDDFT) calculations in either the reciprocal space and frequency domain (LCAO-TDDFT-k-ω) or real space and time domain (LCAO-TDDFT-r-t) of the optical absorption spectra of Chl a and b monomers and dimers. We find that our LCAO-TDDFT-k-ω and LCAO-TDDFT-r-t calculations reproduce results obtained with a plane-wave (PW) representation of the KS wave functions (PW-TDDFT-k-ω) but with a significant reduction in computational effort. Moreover, by applying the Gritsenko, van Leeuwen, van Lenthe, and Baerends solid and correlation derivative discontinuity correction Δx to the KS eigenenergies, with both LCAO-TDDFT-k-ω and LCAO-TDDFT-r-t methods, we are able to semiquantitatively reproduce the experimentally measured photoinduced dissociation results. This work opens the path to first principles calculations of optical excitations in macromolecular systems.