First principles study of sodium-aluminum-hydrogen phases

Heats of formation (DeltaH(f)) and disproportionation reaction enthalpies (DeltaH(R)) were computed for sodium-aluminum-hydrogen (SAH) compounds using a plane density functional methodology and pseudopotentials constructed with the projector augmented wave method. For the 0 K optimized structures, the computed DeltaH(R) compare favorably with available experimental data. The calculations identified ground state hydrogen positions in all known SAH phases, and two structural candidates for the lesser-known high temperature beta-Na3AlH6 phase(s). The structures were analyzed to identify the interatomic orbital hybridizations and charge density distributions. (C) 2003 Elsevier B.V. All rights reserved.