Figure 2: The calculated plots for (a) frequency vs phonon dispersion curves (b) frequency vs density of states.
Infrared and Raman Spectroscopy
We have used Density Functional Perturbation theory [30] in order to revealthe Infrared (IR) and Raman spectroscopy. IR and Raman modes of vibrations obtained for the studied compound are displayed in table 2. As shown in figures (3-4), modes at values of frequency 93.224 cm-1, 113.244 cm-1, 251.0 cm-1 and 436.144 cm-1 are observed due to displacement of Li+and\({\ [\text{BH}_{4}]}^{-}\) ions. At the values of frequency of 1054.1 cm-1 and 1305.3 cm-1, bending modes of vibration occurred due to H and B atoms. The symmetrical modes of vibration have been observed at the values of 2303.5 cm-1, 2387.5 cm-1and 2401.6 cm-1, whereas, antisymmetrical modes of vibration were observed at frequencies of 2345.920 cm-1 and 2377.9 cm-1 due to motion of H atoms. Our calculated Raman active and IR active modes are found to be consistent with the available experimental studies [45]. The calculated modes of vibrations are in close agreement with the earlier theoretical studies with some slightly different modes [31]. The possible reason may be the use of different calculation approaches and the terms related to interactions and exchange potentials etc.
Table 2: Infrared and Raman spectroscopy of LiBH4. Character of modes are represented as inactive (i), Raman active (R), and infrared active (IR) and irreducible representation (Irrep.).