The Perdew, Burke and Ernzerhof (PBE) generalized gradient
approximation (GGA) is the most popular exchange-correlation energy
used in today's ab initio studies. The GGA is tested here in
relation to the intrinsic uncertainty in choosing the degree of
localization of the exchange-correlation hole (the
κ-coefficient in the spin-polarized enhancement factor). The
proposed and most commonly used value of κ = 0.804 (best suited
for atoms and molecules) works well for some solids but should be
modified in many cases in order to predict lattice parameters in
good agreement with experiments. The effect on the structural and
magnetic properties of 3d, 4d and 5d metals including the structural
phase order of Fe is examined using two different state-of-the-art
ab initio implementations of density functional theory: the
full-potential linearized muffin-tin orbital and full-potential
linearized augmented-plane-wave methods. This study gives examples
for the case of elemental d metals of the errors associated with
these properties when using the PBE-GGA in state-of-the-art ab initio electronic structure studies.
The Perturbed-Angular-Correlation technique was used to study the impurity cationic-site population and electric-field gradients in scandium and samarium sesquioxides implanted with 181 Hf → 181 Ta . We found a departure of the tantalum (hafnium) relative occupancy of the crystallographic sites C and D in the bixbyite structure from the natural abundance of the sites, in the case of scandium sesquioxide, that could be explained in terms of the small lattice parameter of this sesquioxide. A similar behavior occurs in the case of indium sesquioxide. In the rest of the bixbyites measured with 181 Ta , f D /f C remains nearly constant and close to the crystallographic abundance, which is only reached in the case of Sm 2 O 3, the sesquioxide with the largest lattice parameter. Additionally, we confirm a jump in the values of νQ( Ta ) for sites C and D that takes place for a ≤ 1:012 nm, that is for lattice parameters smaller than that of ytterbium sesquioxide.
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