LDA or GGA? A combined experimental inelastic neutron scattering and ab initio lattice dynamics study of alkali metal hydrides

G. D. Barrera, D. Colognesi, P. C.H. Mitchell, A. J. Ramirez-Cuesta

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Abstract

In a previous work, we carried out inelastic neutron scattering (INS) spectroscopy experiments and preliminary first principles calculations on alkali metal hydrides. The complete series of alkali metal hydrides, LiH, NaH, KH, RbH and CsH was measured in the high-resolution TOSCA INS spectrometer at ISIS. Here, we present the results of ab initio electronic structure calculations of the properties of the alkali metal hydrides using both the local density approximation (LDA) and the generalized gradient approximation (GGA), using the Perdew-Burke-Ernzerhof (PBE) parameterization. Properties calculated were lattice parameters, bulk moduli, dielectric constants, effective charges, electronic densities and inelastic neutron scattering (INS) spectra. We took advantage of the currently available computer power to use full lattice dynamics theory to calculate thermodynamic properties for these materials. For the alkali metal hydrides (LiH, NaH, KH, RbH and CsH) using lattice dynamics, we found that the INS spectra calculated using LDA agreed better with the experimental data than the spectra calculated using GGA. Both zero-point effects and thermal contributions to free energies had an important effect on INS and several thermodynamic properties.

Original languageEnglish
Pages (from-to)119-129
Number of pages11
JournalChemical Physics
Volume317
Issue number2-3
DOIs
StatePublished - Oct 31 2005
Externally publishedYes

Funding

G.D.B. acknowledges support from the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Centre for Molecular Structure and Dynamics. Ab initio results have been obtained through the use of the ABINIT code, a common project of the Université Catholique de Louvain, Corning Incorporated, and other contributors (URL: http://www.abinit.org ). Useful discussions with Prof. N.L. Allan (University of Bristol) and Dr. Keith Refson (ISIS, Rutherford Appleton Laboratory) are greatly appreciated. A.J.R.-C. acknowledges the award of a Visiting Fellowship in the University of Reading and P.C.H.M. a Leverhulme Emeritus Fellowship.

Keywords

  • Abinitio calculations
  • Alkali metal hydrides
  • Bulk modulus
  • CsH
  • DFT calculations
  • Free energy calculations
  • Hydrogen storage materials
  • INS spectra
  • Inelastic neutron scattering
  • KH
  • LiH
  • NaH
  • RbH
  • Thermodynamic properties

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