  The exact exchange potential in time-dependent density-functional theory is
defined as an orbital functional through the time-dependent optimized effective
potential (TDOEP) method. We numerically solve the TDOEP integral equation for
the real-time nonlinear intersubband electron dynamics in a semiconductor
quantum well with two occupied subbands. By comparison with adiabatic
approximations, it is found that memory effects in the exact exchange potential
become significant when the electron dynamics takes place in the vicinity of
intersubband resonances.

Mesoscale and Nanoscale Physics