This chapter focuses on the practical application of DFT in molecular
systems. We discuss the process of “geometry optimization” and the idea behind it,
which is the very first step of every DFT calculation. We introduce the Gaussian, a
popular software program to perform such calculations. We continue to discuss the
capability of this program with a brief theoretical background, wherever needed. We
talk about several kinds of calculations to be performed by the Gaussian such as
thermodynamics, population analysis, NMR, NLO, NBO, TDDFT calculations to name
a few. More importantly, we discuss how to perform these calculations, extract, and
interpret the results. Ideally, this chapter provides all the ingredients needed to grasp
the results discussed in the forthcoming chapters.
Keywords: DFT, Frequency calculation, Gaussian, GaussView, Geometry
optimization, MESP, Molecular orbital, NBO, NLO, NMR, Population analysis,
TDDFT, Thermodynamics, UV-vis-NIR.