Novel High Pressure Phases of β-AlH3: A Density-Functional Study

Using total energy calculations within the generalized-gradient approximation the high pressure phases, optimized geometry, and electronic structure of AlH3 are established. Among the 58 Structural arrangements considered for the structural optimization calculations. the experimentally known beta modification becomes the C-round-state structure. Application of pressure makes the sequence of phase transitions, from beta --> alpha' --> alpha --> hp1 (P63/m) --> hp2 (Pm (3) over barn) modification and the estimated transition pressures are 2.4. 4.3, 64, and 104 GPa. respectively. The coordination of Al has been changed from six to nine in the newly identified high pressure hp1 and to twelve it) hp2 polymorph. The electronic Structures reveal that alpha,alpha', beta, and gamma polviriorphs are nonmetals with calculated band gap varying between 1.99 and 3.65 eV, whereas the hp1 and hp2 phases possess semiconducting and metallic behavior, respectively.