Currently two different exchange-correlation functionals are implemented: LDA (Ceperley-Alder) and GGA (Perdew-Wang 91). Both are available spin polarized and unpolarized. You can set the exchange-correlation functional with:
exchange_correlation name_of_functional.
By default:
exchange_correlation ceperley_alder
The GGA can be switched on with:
exchange_correlation perdew_wang_91
WARNING: The current implementation of this GGA has trouble if there
are regions of small charge density. This is typically causing
problems for isolated molecules, where the charge decays to very small
values. In that case, the critical regions will be omitted, and the
code will print a warning saying what percentage of the charge is in
such critical regions.
WARNING: THE STRESS (AND FORCE?) CONTRIBUTIONS DUE TO GGA ARE NOT
IMPLEMENTED YET, SO THE STRESS (AND FORCE?) ARE WRONG!