Extension of the basis set of linearized augmented plane wave method (LAPW) by using supplemented tight binding basis functions

In order to increase the accuracy of the linearized augmented plane wave method (LAPW) we present a new approach where the plane wave basis function is augmented by two different atomic radial components constructed at two different linearization energies corresponding to two different electron bands (or energy windows). We demonstrate that this case can be reduced to the standard treatment within the LAPW paradigm where the usual basis set is enriched by the basis functions of the tight binding type, which go to zero with zero derivative at the sphere boundary. We show that the task is closely related with the problem of extended core states which is currently solved by applying the LAPW method with local orbitals (LAPW+LO). In comparison with LAPW+LO, the number of supplemented basis functions in our approach is doubled, which opens up a new channel for the extension of the LAPW and LAPW+LO basis sets. The appearance of new supplemented basis functions absent in the LAPW+LO treatment is closely related with the existence of the $dot{u}_l-$component in the canonical LAPW method. We discuss properties of additional tight binding basis functions and apply the extended basis set for computation of electron energy bands of lanthanum (face and body centered structures) and hexagonal close packed lattice of cadmium. We demonstrate that the new treatment gives lower total energies in comparison with both canonical LAPW and LAPW+LO, with the energy difference more pronounced for intermediate and poor LAPW basis sets.

Hyperfine field assessment of the magnetic structure of ZrZn2

Time differential perturbed angular gamma-gamma-correlation (TDPAC) method on 111Cd nuclei probes inserted in ZrZn1.9 is used to measure the magnetic hyperfine fields (MHF) at Zr and Zn sites and the electric field gradient (EFG) Vzz at Zn sites as a function of temperature at various pressures and as a function of pressure at the temperature 4 K. Our data indicate that the local magnetic moment of Zr in the magnetically ordered state is substantially larger than its value obtained from the macroscopic measurements and that there is also an induced magnetic moment at the Zn site. We conclude that ZrZn2 is not a simple ferromagnet and discuss a possible type of its magnetic ordering.