Nitty-Gritties

The efficiency of the LAPW basis derives from its use of carefully chosen representations of the wavefunctions in different regions. In particular, a spherical harmonics expansion on a radial mesh is used inside the spheres and a planewave expansion outside. With this choice, rapid variations of the wavefunctions inside the spheres pose no particular problems, and accordingly the method is well suited to all-electron calculations (i.e. no pseudopotential) as well as d- and f-electron materials. However, rapidly varying wavefunctions imply rapidly varying charge densities and potentials, and this requires that the representations of the charge density and potential be equally flexible.