title: Ab initio theoretical investigation of beryllium and beryllium hydride nanoparticles and nanocrystals with implications for the corresponding infinite systems.
abstract: With the initial motivation of optimizing hydrogen storage in beryllium nanocrystals, we have thoroughly and systematically studied the structural, cohesive, and electronic properties of Ben and BenHxn (n = 2-160, x = 0.1-2.4) nanoparticles as a function of both size (n) and hydrogen content (x), using density functional theory with a properly selected meta-hybrid functional and high level coupled cluster CCSD(T) theory for comparison. We have calculated the binding energies of Ben, BenHxn and [BeH2]n nanoparticles for a large range of n values. In the limit n→∞, we have obtained the experimental binding energy of a Be crystal (3.32 eV) with unexpectedly very good agreement (3.26 ± 0.06 eV), and a predicted value of 7.85 eV ± 0.02 eV for the binding energy of the [BeH2]∞ infinite system. We also predict that the majority of the lowest energy stoichiometric BenH2n nanoparticles are chains or chain-like structures. The tendency towards chain stabilization of BenHxn nanoparticles increases, as x approaches the stoichiometric value x = 2, leading for large values of n, as n→∞, to polymeric forms of bulk BeH2, which in the past have been considered as the leading forms of solid BeH2. For such 1-dimensional forms of [BeH2]n we have obtained and verified that the binding energy varies exactly proportionally to n(-1). The extrapolated desorption energy for such polymeric forms of solid BeH2 is found to be 19 ± 3 kJ mol(-1) in juxtaposition to the experimental value of 19 kJ mol(-1) for solid BeH2, suggesting that the difference ΔE in cohesive energy between the orthorhombic and polymeric form is very small (ΔE≈ 3 kJ mol(-1)). This is in full accord with the early discrepancies in the literature in determining and distinguishing the real crystal structure of solid BeH2.
authors.affiliation: Molecular Engineering Laboratory, Department of Physics, University of Patras, Patras 26500 GR, Greece. zdetsis@upatras.gr.
authors.forename: Aristides D
authors.initials: AD
authors.lastname: Zdetsis
authors.forename: Michael M
authors.initials: MM
authors.lastname: Sigalas
authors.forename: Emmanuel N
authors.initials: EN
authors.lastname: Koukaras