Computational theory of condensed matter deals with a diverse set of systems, where the common denominator is complexity. A molecule in contact with a macroscopic lead is an example. Other examples are systems with reduced dimensionality and inhomogeneous systems. These systems host a number of degrees of freedom, such as charge and spin, electrons and phonons or more complicated, emergent quasiparticles. Theoretical “paper and pencil” techniques can be helpful, but are usually not applicable. Here we treat these problems computationally, inspired by hot experimental advancements.