Think Outside the Lab: Modeling Graphene Quantum Dots in Pandemic Times

A computational laboratory experiment is carried out to investigate the size-, geometry-, and chemistry-dependent properties of small molecules known as polycyclic aromatic hydrocarbons (PAHs) at the Facultad de Ingenieria (Universidad Nacional de La Plata, UNLP), Buenos Aires, Argentina. This computational research was adapted for upper-division undergraduate and initial graduate education levels. Due to the adverse circumstances of the pandemic, students were challenged to perform theoretical calculations on a regular computer at home. They were able to model PAH molecules similar to graphene quantum dots (GQDs) and learn how to use various open and freely available softwares, including visual molecular dynamics (VMD), Avogadro, nanoHUB.org, and ORCA. Through these computational tools, students designed PAHs of various sizes, geometries, and functional groups in order to study some of their optoelectronic properties. They simulated UV-vis absorbance spectra based on changes in size, geometry, and chemistry at the edges of the GQDs. Students then calculated the energy of the HOMO-LUMO gap and compared using three different methods included in ORCA corresponding to Hartree-Fock (H-F) approximation, density functional theory (DFT), and time-dependent DFT (TD-DFT). Finally, based on the results obtained, students propose the construction of more efficient solar devices by tuning the size and geometry of GQDs.