Speaker
Prof.
John Rehr
(University of Washington)
Description
We calculate x-ray absorption spectra (XAS) of water within a
GW/Bethe-Salpeter Equation (BSE) approach using the
OCEAN code [1-3]. This hybrid code combines ab initio plane-
wave, pseudopotential electronic structure, PAW transition-
matrix elements, GW self-energy corrections, and the NIST
BSE solver [1]. Due to the computational demands, our
previous XAS calculations [2] were limited to 17 molecule
super cells. This limitation causes unphysical, size dependent
effects in the calculated spectra. In order to treat much larger
systems several improvements were necessary [3]: 1) we
extended the OCEAN interface to support well-parallelized
codes such as QuantumESPRESSO; 2) we implemented an
efficient interpolation scheme due to Shirley. We have
applied this large-scale GW/BSE approach to 64 molecule unit
cell structures of water obtained from classical DFT/MD and
PIMD simulations [4]. In comparison with previous work [5],
we obtain improved spectra that agree semi-quantitatively
with experimental features. The agreement suggests that the
64 molecule unit cell PIMD structures, which are similar to
the traditional distorted tetrahedral view, are consistent with
experimental observations.
[1] J. Vinson et al., PRB 83, 115106 (2011); J. Vinson and
J.J. Rehr, PRB 86, 195135 (2012).
[2] J. Vinson et al., PRB 85, 045101 (2012).
[3] K. Gilmore, J. Vinson, E.L. Shirley, D. Prendergast, J. J.
Kas and J. J. Rehr, UW Preprint 2014.
[4] J.A. Morrone and R. Car, PRL 101, 017801 (2008).
[5] L. Kong et al., PRB 86, 134203 (2012).
Co-authors
F Vila
(University of Washington)
J Kas
(University of Washington)
J Vinson
(National Institute of Standards and Technology)
K Gilmore
(European Synchrotron Radiation Facility)
