This chapter discusses the fundamentals of density functional theory (DFT), used in electronic structure simulation methods for the in silico estimation of physicochemical properties of nanomaterials (NMs). These nanodescriptors are used, for instance, in the development of statistical models for toxicological risk assessment of NMs. The experimental characterization of the toxicological profiles of NMs is an expensive and time-consuming task. The chapter aims to provide an overview of electronic structure simulations and their applications in computational material science to obtain physicochemical properties that can be used as nanodescriptors for the toxicological assessment of NMs. It focuses on DFT methods since they are the most used for the prediction of material properties and chemical reactions. DFT methods have very favorable characteristics, and numerous scientists from different areas employ them to compute and predict properties in numerous systems. The main advantage of linear-scaling DFT is that one can perform simulations of hundreds of thousands of atoms at a relatively small computational cost.