On Sab, Maggio 3, 2008 00:10, alan chen wrote: > What does it really mean? Is there a > local potential if we set "lloc = -1"?
Dear Hanghui, when generating the psedopotential you want to reproduce the scattering properties of the all-electron core with a local potential and some projectors functions. The projectors works at short radius, and compensate the inability of a simple local potential to produce the desired solutions for all energies and angular momenta. Usually you can choose one special angular momentum and a reference energy to be used as local channel; this has several implications: the local channel has to be norm-conserving, cannot have a second reference energy, cannot have ghost states. So usually you want to choose the higher possible L for the local channel to reduce the number of projectors (you have one for each M=-L,..,L). Instead you often wind up taking a lower L in order to remove a ghost state. The point is that it is not a must to use a local channel, actually as long as it matches the all-electron potential outside the pseudization region, you can take *any* function as a local potential. As a drawback you will have to use (at least) one projector for each value of L; this can make you pseudopotential slower or less transferable. Sometimes it is the only way to avoid the presence of ghost states. -- Lorenzo Paulatto SISSA & DEMOCRITOS (Trieste) +39 040 3787 511 http://people.sissa.it/~paulatto/ ---------------------------------------------------------------- SISSA Webmail https://webmail.sissa.it/ Powered by SquirrelMail http://www.squirrelmail.org/
