Electronic structure and optical properties of complex hydrides LiBH4 and NaAlH4 compounds

The properties of the complex hydrides LiBH₄ and NaAlH₄ such as structural, electronic, and optical properties were calculated using the augmented plane wave plus local orbitals (APW + lo) method. The three phases α, β, and γ of LiBH₄ and NaAlH₄ hydrides are studied, the β‐phase is transformed at the high‐pressure to γ phase for the compound LiBH₄ with the generalized gradient approximation (GGA) with a 16% volume decrease. However, NaAlH₄ compound did not show any phase transition. The interaction between the boron (aluminum) atoms and the hydrogen atoms in the [AlH₄]^? ([BH₄]^? ) complexes is strongly covalent, and between the complexes [AlH₄]^? and the lithium Li⁺ cations for the LiBH₄ compound and between the complexes [AlH₄]^? and the sodium Na⁺ cations for the NaAlH₄ compound, the bond is ionic. For the most stable phases of the two complex hydrides, different optical parameters have been calculated as a function of the photon energy. The plasma frequency ω_p is calculated from the mean peak of the energy loss function. Therefore, by way of example, the plasma energy ?ω_p of its peak position is 13.23 (12.93) eV for α‐NaAlH₄ (α‐LiBH₄).