Abstract: Linear scaling formalisms of density-functional theory (DFT) exploit the nearsightedness principle in order to treat systems of several thousand atoms. One popular approach, which has been implemented in the wavelet based BigDFT code, uses localized orbitals, which are optimized to reflect their local chemical environment and thus constitute a minimal but accurate basis set. This also offers additional flexibility, such as the straightforward definition of a fragment approach, which is particularly useful for disordered supramolecular materials and provides a convenient framework for constrained DFT. I will present the key features of this approach, focussing in particular on how it can be used to calculate charge transport parameters in a host-guest OLED material. Through this example I will demonstrate how large scale DFT is a powerful tool which enables first principles simulations to go beyond model structures of a few molecules, to realistic disordered morphologies containing thousands of atoms, allowing environmental and statistical effects to be taken into account