All-electron Linear Augmented Plane Wave Research Articles

All electron GW with linearized augmented plane waves for metals and semiconductors

GW approximation is one of the most popular parameter-free many-body methods that go beyond the limitations of the standard density functional theory (DFT) to determine the excitation spectra for moderately correlated materials and in particular the semiconductors. It is also the first step in developing the diagrammatic Monte Carlo method into an electronic structure tool, which would offer a numerically exact solution to the solid-state problem. While most electronic structure packages offer support for GW calculations for band-insulating materials, the level of support for metallic systems is somewhat limited. This limitation can be partly attributed to the relatively minor differences often observed between GW and DFT results in treating metallic systems, which is not expected to persist to higher orders in perturbation theory. Describing metals within the GW framework presents a challenge, as it requires accurate resolution of Fermi surface singularities, which, in turn, calls for a dense momentum mesh. Here we implement the GW algorithm within the all-electron Linear Augmented Plane Wave framework, where we pay special attention to the metallic systems, the convergence with respect to momentum mesh, and proper treatment of the deep laying core states, as needed for the future variational diagrammatic Monte Carlo implementation. Our improved algorithm for resolving Fermi surface singularities allows us a stable and accurate analytic continuation of imaginary axis data, which is carried out for GW excitation spectra throughout the Brillouin zone in both the metallic and insulating materials and is compared to numerically more stable contour deformation integration technique. We compute band structures for elemental metallic systems Li, Na, and Mg as well as for various narrow and wide bandgap insulators such as Si, BN, SiC, MgO, LiF, ZnS, and CdS and compare our results with previous GW calculations and available experiments data. Our results are in good agreement with the available literature. Thus our software allows users to compute full bandstructures for metals and insulators using all-electron potential without downfolding to Wannier orbital basis.

Ab initiolinear response and frozen phonons for the relaxorPbMg1∕3Nb2∕3O3

We report first principles density functional studies using plane wave basis sets and pseudopotentials and all-electron linear augmented plane wave (LAPW) of the relative stability of various ferroelectric and antiferroelectric supercells of PMN $(\mathrm{Pb}{\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3})$ for 1:2 chemical ordering along [111] and [001]. We used linear response with density functional perturbation theory as implemented in the code ABINIT to compute the Born effective charges, electronic dielectric tensors, long wavelength phonon frequencies and longitudinal optic-transverse optic (LO-TO) splittings. The polar response is different for supercells ordered along [111] and [001]. Several polar phonon modes show significant coupling with the macroscopic electric field giving giant LO-TO splittings. For [111] ordering, a polar transverse optic mode with $E$ symmetry is found to be unstable in the ferroelectric $P3m1$ structure and the ground state is found to be monoclinic. Multiple phonon instabilities of polar modes and their mode couplings provide the pathway for polarization rotation. The Born effective charges in PMN are highly anisotropic and this anisotropy contributes to the observed huge electromechanical coupling in PMN solid solutions.

Structural stability ofPu(1−x)Mx(M=Al,Ga, and In) compounds

We present results on the structural stability of ${\mathrm{Pu}}_{(1\ensuremath{-}x)}{M}_{x}$ $(M=\mathrm{A}\mathrm{l},\mathrm{G}\mathrm{a},\mathrm{I}\mathrm{n})$ compounds in the framework of density functional theory within the local density approximation and generalized gradient approximation (GGA). An all-electron linear augmented plane wave method, which includes an additional ${p}_{1/2}$ local orbital in spin orbit coupling, is used in order to determine the formation energy of these compounds. Using the GGA and spin polarized calculations, the calculated structural hierarchy is in agreement with the trends observed in the experimental phases diagrams. The stability of the Pu-M compounds can be related to a strong pdf hybridization.