  We perform binary neutron star (BNS) merger simulations in full dynamical
general relativity with IllinoisGRMHD, on a Cartesian grid with adaptive-mesh
refinement. After the remnant black hole has become nearly stationary, the
evolution of the surrounding accretion disk on Cartesian grids over long
timescales (1s) is suboptimal, as Cartesian coordinates over-resolve the
angular coordinates at large distances, and the accreting plasma flows
obliquely across coordinate lines dissipating angular momentum artificially
from the disk. To address this, we present the Handoff, a set of computational
tools that enables the transfer of general relativistic magnetohydrodynamic
(GRMHD) and spacetime data from IllinoisGRMHD to HARM3D, a GRMHD code that
specializes in modeling black hole accretion disks in static spacetimes over
long timescales, making use of general coordinate systems with spherical
topology. We demonstrate that the Handoff allows for a smooth and reliable
transition of GRMHD fields and spacetime data, enabling us to efficiently and
reliably evolve BNS dynamics well beyond merger. We also discuss future plans,
which involve incorporating advanced equations of state and neutrino physics
into BNS simulations using the \handoff approach.
