Density-functional theory (DFT) is one of the biggest fields in todays condensed-matter and materials science. It constitutes a precise and practical way to predict and interpret many material properties. DFT is a computational method to calculate the groundstate electron-density of systems like molecules and crystals. DFT is concerned with solving the Kohn-Sham equation. The DFT toolbox contains many codes, which differ mostly by the choice of the basis set on which the Kohn-Sham wave functions are represented. One of those is the LAPW ( linearized augmented plane-wave) basis set. This thesis presents a variety of implementations for the exciting code from the fields of numerical mathematics, user interfaces and general scientific software development. We examine possible optimizations, also within respect to enable the exciting code to run on parallel computer architectures. The presented optimizations involve the k-point parallelization, finding a better solver for the generalized eigenvalue problem, and convergence improving algorithms for the self consistent field loop. We introduce new input and output methods using XML which serves as the base for a new concept for the graphical user interface and results database exciting@web. Finally we discuss the necessary changes in the development process to allow for a better collaboration on the exciting code.