Parameter choice for GAPW

[Axel]

hi!

i'd appreciate it, if somebody could shed some light on how to
justify
parameter choices for GAPW calculations. the input reference mostly
contains statements of the kind XXX sets the value for 'xxx', which
are
probably of most use to the person who knows the implemention very
well
(which i obviously don't :-) ).

from looking through the regtests and the input reference it seems to
me
that ALHPA0_HARD and ALHPA0_SOFT, LMAXN0, LMAXN1 in %FORCE_EVAL%DFT
%QS
seem to be the most important global options, and that LEBEDEV_GRID,
RADIAL_GRID, and HARD_EXP_RADIUS in %FORCE_EVAL%SUBSYS%KIND seem to be
the most
important per atom type parameters.

are there any do's and don'ts associated with those parameters, e.g.
what needs to
be changed when going from a bulk water system to a compound with
"heavy" elements?
which of those parameters are related to higher angular momentum and
thus need to
be increased or decreased? can the HARD_EXP_RADIUS and its sibling
RHO0_EXP_RADIUS
be understood in a similar way as the ultrasoft cutoff radius for
USPPs?

thanks in advance,
     axel.