The importance of vibrations in modelling complex metal hydrides

Frankcombe, Terry J.

doi:10.1016/j.jallcom.2007.01.050

Cited by 18 publications

(19 citation statements)

References 25 publications

(34 reference statements)

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“…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.…”

Section: Resultssupporting

confidence: 85%

“…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.…”

Section: Resultsmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Marashdeh

Frankcombe

2008

The Journal of Chemical Physics

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The dehydrogenation enthalpies of Ca͑AlH 4 ͒ 2 , CaAlH 5 , and CaH 2 + 6LiBH 4 have been calculated using density functional theory calculations at the generalized gradient approximation level. Harmonic phonon zero point energy ͑ZPE͒ corrections have been included using Parlinski's direct method. The dehydrogenation of Ca͑AlH 4 ͒ 2 is exothermic, indicating a metastable hydride. Calculations for CaAlH 5 including ZPE effects indicate that it is not stable enough for a hydrogen storage system operating near ambient conditions. The destabilized combination of LiBH 4 with CaH 2 is a promising system after ZPE-corrected enthalpy calculations. The calculations confirm that including ZPE effects in the harmonic approximation for the dehydrogenation of Ca͑AlH 4 ͒ 2 , CaAlH 5 , and CaH 2 + 6LiBH 4 has a significant effect on the calculated reaction enthalpy. The contribution of ZPE to the dehydrogenation enthalpies of Ca͑AlH 4 ͒ 2 and CaAlH 5 calculated by the direct method phonon analysis was compared to that calculated by the frozen-phonon method. The crystal structure of CaAlH 5 is presented in the more useful standard setting of P2 1 / c symmetry and the phonon density of states of CaAlH 5 , significantly different to other common complex metal hydrides, is rationalized.

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Section: Resultssupporting

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Marashdeh

Frankcombe

2008

The Journal of Chemical Physics

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“…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.…”

Section: Methodsmentioning

confidence: 99%

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

Liu

et al. 2018

International Journal of Hydrogen Energy

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Vanadium-based alloys are promising for the reversible, compressed storage of renewable hydrogen. To improve the hydrogen desorption plateau pressure of vanadium hydrides, V-3A binary alloys (i.e. V 97 Al 3 , V 97 Mn 3 , and V 97 Ru 3) were prepared by vacuum arc melting. Hydrogen absorption and desorption properties of the newly prepared V-3A samples were studied, and compared to vanadium hydrides, by pressure-composition-temperature measurements and first-principles calculations. Among V-3A binary alloys, V 97 Ru 3 achieved the highest hydrogen desorption plateau pressure while accommodating the highest atomic percentage of hydrogen. Meanwhile, it was also the alloy with the highest measured hardness. 2 Hydrogen desorption plateau pressures of V-3A alloys were complemented with DFT calculated formation energies. Calculated DOS, ELF and Bader charges showed that the influence of alloying on the electronic properties of the hydrides was comparable for Mn and Ru; whereas for Al alloying, vanadium dihydride bonding interactions were modified the most.

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“…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.…”

Section: Resultsmentioning

confidence: 96%

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

Kim

2012

Int J of Quantum Chemistry

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The double cation borohydride NaSc(BH4)4 has a total H2 content of 12.67 wt.% and has been suggested as a potential candidate for hydrogen storage applications. This study reports first‐principles calculations of the structure and reaction thermodynamics of NaSc(BH4)4. The calculations indicate that NaSc(BH4)4 is decomposed into a mixture of ScB2, NaBH4, and Na2(B10H10) with H2 release of 9.3 wt.% at 118 K at a partial pressure of H2 of 100 bar. Reactant compositions that can destabilize NaSc(BH4)4 were evaluated. This effort identified four destabilization reactions that are predicted to have reaction thermodynamics for hydrogen release within the temperature range of 78–109 K. Even though the reactions conclusively produce undesired compounds, such as refractory materials or kinetically stable B12H12‐containing species, the thermodynamic study suggests a direction for improving the thermodynamics of double cation borohydride‐based systems being actively considered for hydrogen storage applications. © 2012 Wiley Periodicals, Inc.

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The importance of vibrations in modelling complex metal hydrides

Cited by 18 publications

References 25 publications

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

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

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

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

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The importance of vibrations in modelling complex metal hydrides

Cited by 18 publications

References 25 publications

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

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

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

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

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