Three new stable bialkalimetallic alanates are predicted by
accurate density functional calculations: \chem{K_2LiAlH_6},
\chem{K_2NaAlH_6}, and \chem{KNa_2AlH_6}. Their detailed crystal
structure has been determined by a systematic search through a
large part of the probable space of crystal structures. They are
thermodynamically stable at 0\un{K} compared to their monoalkali
constituents by 9 to 49\un{kJ/mol} formula units. The crystal
structure of the already known alanates \chem{Li_3AlH_6},
\chem{Na_3AlH_6}, \chem{K_3AlH_6}, and \chem{LiNa_2AlH_6} were
also determined, and found to be in excellent agreement with
experimental data where available. The two last bialkali alanates
studied, \chem{Li_2NaAlH_6} and \chem{KLi_2AlH_6}, were found to
be unstable
