  The nonequilibrium variational-cluster approach is applied to study the
real-time dynamics of the double occupancy in the one-dimensional Fermi-Hubbard
model after different fast changes of hopping parameters. A simple reference
system, consisting of isolated Hubbard dimers, is used to discuss different
aspects of the numerical implementation of the approach in the general
framework of nonequilibrium self-energy functional theory. Opposed to a direct
solution of the Euler equation, its time derivative is found to serve as
numerically tractable and stable conditional equation to fix the time-dependent
variational parameters.
