Hi to all,
I have done some slab calculations using SIESTA. Compared with
ABINIT, it actually has not any huge computational burden and the SCF
convergence looks very well. To my knowledge, SIESTA is in the
localized-basis set framework, while ABINIT in a plane-wave-function
framework. then the question is does SIESTA perform an isolated-slab
calculation, or a periodic-slab one like ABINIT?
Dear Yong,
SIESTA, as ABINIT, imposes periodic boundary conditions. That means
that yes, it will do a periodic-slab calculation, as ABINIT.
As far as I know, there is no way to make it use a different kind of
boundary conditions. Thus, if you need to study an isolated slab, you
need to surround it by enough empty space in your dimension
perpendicular to the slab to make sure that the orbitals don't overlap
with those of the "image" systems. You can check that in the SIESTA
output, by looking for a line such as
siesta: System type = slab
A different type will indicate overlap along 1 (chain), 0 (molecule),
or 3 (bulk) dimensions.
I'd say that, though the use of PBCs is not mandatory since, as you
mentioned, SIESTA uses localized orbitals, it is probably imposed by
using a Poisson solver that works by doing Fourier transforms, which do
require PBCs.
Xavier
