High-pressure study of hydrogen storage material ethylenediamine bisborane from first-principle calculations

Ethylenediamine bisborane (EDAB), as a hydrogen storage material, is one of the most promising possible candidates. This work reports the effects of pressure on the structural, mechanical, electronic, and vibrational behaviors of EDAB using density functional theory calculations. The predicted lattice parameters, bulk modulus B₀ and its first pressure derivative B^′ are in accord with available experimental data. From the unit-cell constants as a function of pressure, crystal EDAB is found to present an anisotropic compressibility. The calculated elastic properties show that the ambient phase EDAB is mechanical unstable at 3 GPa. Furthermore, the discontinuous behavior was found in the pressure dependence of crystal and electronic structure, suggesting a structural transformation occurred around 3 GPa. Finally, vibrational spectra are reported together with their infrared active modes assignment. The NH and BH stretching modes soften under compression, indicating the strengthening of hydrogen bonding, which leads to the occurrence of pressure-induced structural transformation.