Excited states and optical properties entirely from first principles: Extended FLAPW method and its graphical user interface

This review serves to explain in some detail the nature and unique treatment of optical properties entirely from first-principles within the powerful FLAPW code and its accompanying sophisticated GUI. One unique feature of the method and its code is the viewing and printing of the various calculated optical properties - Im (eps), Re (eps), N, K, R, EELS and alpha - in the same way as the band structure, charge and spin densities and the density of states were done in the previous version of the FLAPW code. Another unique feature is the ability to calculate the optical properties in several modes, with the LDA and/or the model GW and the sX-LDA approaches (each with and without the inclusion of spin-orbit coupling). The code is also designed to carry out accurate calculations of the optical properties of dilutely doped semiconductors employing several dilute limit simulation tools: these include k-mesh refinement around a certain k-point within a given radius, edge refinement (which refines the tetrahedra around the Fermi energy to get an accurate absorption edge), a further k-mesh refinement to take account the user-specified (or calculated) Fermi level that reflects the dopant or defect concentration, simulation of temperature effects with the Fermi-Dirac statistics, etc.