The importance of vibrations in modelling complex metal hydrides

Ca ( Al H 4 ) 2 , CaAlH5, and CaH2+6LiBH4: Calculated dehydrogenation enthalpy, including zero point energy, and the structure of the phonon spectra

“…For the "elementary" steps ͓that is, excluding the overall reaction ͑3͔͒, the magnitudes of the reductions were of the order that has come to be expected. 8 Without ZPE, our calculated enthalpy changes are in accord with those published by Alapati et al 16 for reactions ͑3͒ and ͑4͒. The small discrepancies are easily accounted for as differences in details such as energy and geometry optimization convergence thresholds.…”

“…The phonon density of states of Ca͑AlH 4 ͒ 2 exhibited similar features to densities of states calculated for other similar complex metal hydrides. 8,10,28 Specifically, the density of states could be separated into three clearly identifiable groups of modes. The states contributing to the density at high frequencies corresponded to Al-H stretching motion.…”

“…1 It is now well known that including ZPE effects ͑in the harmonic approximation͒ for the dehydrogenation of complex metal hydrides has a significant effect on the calculated reaction enthalpy. [8][9][10][11][12] Including ZPE contributions typically reduces the calculated energy change by 10-20 kJ/ mol H 2 , 8 a range sufficiently predictable that it can be used to speed potential hydrogen storage system screening. 13 Wolverton and Ozoliņš have calculated the ZPE corrected dehydration enthalpies for reactions ͑1͒-͑3͒ using the frozen-phonon method.…”

Effects of alloying elements (Al, Mn, Ru) on desorption plateau pressures of vanadium hydrides: An experimental and first-principles study

“…All the newly generated alloys and hydrides were fully optimized until the total forces acting on each atom were smaller than 0.01 eV/Å. The zero-point energy (ZPE), particularly for compounds that contain lightweight elements such as hydrogen, is not negligible [26][27][28][29][30]. Therefore, in addition to the formation energy of the hydrides, here we also report the ZPE corrected formation energies.…”

Crystal structures and thermodynamic investigations of NaSc(BH4)4 from first‐principles calculations

“…Sholl and coworkers27 examined the crystal structure of LiK(BH 4 ) 2 using the GGA‐PW91 functional, predicting a structure having a cell volume 3.78% smaller than the experiment. There are also reports addressing that such potential energy minimizations give smaller volume cells than those from diffraction experiments 29, 30. A deviation of the DFT optimized structure of NaSc(BH 4 ) 4 from the experiment is therefore reasonable.…”