LANS Informal Seminar: André Schleife

Seminar Title: Numerical integrators for a plane-wave implementation of real-time time-dependent density functional theory
Speaker: André Schleife, Blue Waters Assistant Professor, Department of Materials Science and Engineering, UIUC

Date/Time: 2015-09-17 10:30
Location: Bldg. 240, rm. 4301

Description:
The adiabatic Born-Oppenheimer approximation is prevalent in
electronic-structure simulations and molecular dynamics studies, since
it significantly reduces computational cost, however, within this
approximation ultrafast electron dynamics is inaccessible. Achieving a
computationally affordable, accurate description of real-time electron
dynamics through time-dependent quantum-mechanical theory arguably is
one of the greatest challenges in computational materials physics and
chemistry today.

Several groups are currently exploring real-time time-dependent density
functional theory as a possible route and we recently implemented this
technique into the highly parallel Qbox/Qb@ll codes. The numerical
integration of the time-dependent Kohn-Sham equations is highly
non-trivial: Using a plane-wave basis set leads to large Hamiltonians
which constrains what integrators can be used without losing
computational efficiency. Here, we studied various integrators for
propagating the single-particle wave functions explicitly in time, while
achieving high parallel scalability of the plane-wave pseudopotential
implementation. We compare a fourth-order Runge-Kutta scheme that we
found to be conditionally stable and accurate to an enforced time
reversal symmetry algorithm. Both are well-suited for highly
parallelized supercomputers as proven by excellent performance on a
large number of nodes on Blue Gene based Sequoia” at LLNL and Cray
XE6 based ”Blue Waters” at NCSA. This allows us to apply our scheme to
materials science simulations involving hundreds of atoms and thousands
of electrons.”