  We study the time-dependent neutralization of a slow highly charged ion that
penetrates a hexagonal hollow-centred graphene nanoflake. To compute the
ultrafast charge transfer dynamics, we apply an effective Hubbard nanocluster
model and use the method of nonequilibrium Green functions (NEGF) in
conjunction with an embedding self-energy scheme which allows one to follow the
temporal changes of the number of electrons in the nanoflake. We perform
extensive simulations of the charge transfer dynamics for a broad range of ion
charge states and impact velocities. The results are used to put forward a
simple semi-analytical model of the neutralization dynamics that is in very
good agreement with transmission experiments, in which highly charged xenon
ions pass through sheets of single-layer graphene.
