  Our aim is to study the thermal and dynamical evolution of protoplanetary
disks in global simulations, including the physics of radiation transfer and
magneto-hydrodynamic (MHD) turbulence caused by the magneto-rotational
instability. We develop a radiative transfer method based on the flux-limited
diffusion approximation that includes frequency dependent irradiation by the
central star. This hybrid scheme is implemented in the PLUTO code. The focus of
our implementation is on the performance of the radiative transfer method.
Using an optimized Jacobi preconditioned BiCGSTAB solver, the radiative module
is three times faster than the MHD step for the disk setup we consider. We
obtain weak scaling efficiencies of 70% up to 1024 cores. We present the first
global 3D radiation MHD simulations of a stratified protoplanetary disk. The
disk model parameters are chosen to approximate those of the system AS 209 in
the star-forming region Ophiuchus. Starting the simulation from a disk in
radiative and hydrostatic equilibrium, the magnetorotational instability
quickly causes MHD turbulence and heating in the disk. For the disk parameters
we use, turbulent dissipation heats the disk midplane and raises the
temperature by about 15% compared to passive disk models. A roughly flat
vertical temperature profile establishes in the disk optically thick region
close to the midplane. We reproduce the vertical temperature profile with a
viscous disk models for which the stress tensor vertical profile is flat in the
bulk of the disk and vanishes in the disk corona. The present paper
demonstrates for the first time that global radiation MHD simulations of
turbulent protoplanetary disks are feasible with current computational
facilities. This opens up the windows to a wide range of studies of the
dynamics of protoplanetary disks inner parts, for which there are significant
observational constraints.
