Speeding up the solution of the Bethe-Salpeter equation by a double-grid method and Wannier interpolation

Abstract

5 pages, 3 figures. Accepted for Phys. Rev. BInternational audienceThe Bethe-Salpeter equation is a widely used approach to describe optical excitations in bulk semiconductors. It leads to spectra that are in very good agreement with experiment, but the price to pay for such accuracy is a very high computational burden. One of the main bottlenecks is the large number of k-points required to obtain converged spectra. In order to circumvent this problem we propose a strategy to solve the Bethe-Salpeter equation based on a double-grid technique coupled to a Wannier interpolation of the Kohn-Sham band structure. This strategy is then benchmarked for a particularly difficult case, the calculation of the absorption spectrum of GaAs, and for the well studied case of Si. The considerable gains observed in these cases fully validate our approach, and open the way for the application of the Bethe-Salpeter equation to large and complex systems

Ab initioelectronic structure, optical, and magneto-optical properties of MnGaAs digital ferromagnetic heterostructures

“…(2) up to a kinetic energy cutoff of 4 Ry. The absorption of bulk GaAs is instead computed with a double-grid sampling of the BZ [23] with a regular 12 × 12 × 12 mesh shifted from plus a random mesh of 2000 k points. In this case the well-established value [24] of 0.8 eV opening of the band gap has been used for the QP correction.…”

Optoelectronic properties ofTa3N5: A joint theoretical and experimental study

“…The optical absorption spectra were obtained by solving the Bethe-Salpeter Equation (BSE), [8][9][10] starting from our G 0 W 0 results and employing the double-grid method for k-point sampling. 22 …”

“…Since BSE calculations generally require a large number of k-points, we employed the double-grid method proposed in Ref. 22 to speed up the convergence. Figure 4 shows the absorption coefficient (α) of Ta 3 N 5 computed at the BSE/G 0 W 0 level of theory, compared with the experimental result obtained with UV-Vis spectroscopy.…”

Ab initiocalculations of exciton radiative lifetimes in bulk crystals, nanostructures, and molecules

“…Due to the light electron mass, which leads to a steep conduction band valley, fully converging the radiative lifetimes in GaAs requires very fine Brillouin zone grids with a large computational cost. Using a double-grid technique, Kammerlander et al [47] have shown that a 40 × 40 × 40 k-point grid is sufficient to converge the BSE absorption spectrum. Since the radiative lifetimes depend on the energy and transition dipole of the lowest-energy excitons, the k-point convergence of the lifetimes is similar to that of the absorption spectrum.…”

“…Using the standard BSE (without the double-grid technique of Ref. 47), the finest grid we were able to reach is a 30 × 30 × 30 k-point grid, which took over 10, 000 CPU cores to compute. Since our grid is close to the fully converged 40 × 40 × 40 k-point grid, it allows us to obtain results close to convergence.…”