  We present the implementation of a radiative transfer solver with coherent
scattering in the new BIFROST code for radiative magneto-hydrodynamical (MHD)
simulations of stellar surface convection. The code is fully parallelized using
MPI domain decomposition, which allows for large grid sizes and improved
resolution of hydrodynamical structures. We apply the code to simulate the
surface granulation in a solar-type star, ignoring magnetic fields, and
investigate the importance of coherent scattering for the atmospheric
structure. A scattering term is added to the radiative transfer equation,
requiring an iterative computation of the radiation field. We use a
short-characteristics-based Gauss-Seidel acceleration scheme to compute
radiative flux divergences for the energy equation. The effects of coherent
scattering are tested by comparing the temperature stratification of three 3D
time-dependent hydrodynamical atmosphere models of a solar-type star: without
scattering, with continuum scattering only, and with both continuum and line
scattering. We show that continuum scattering does not have a significant
impact on the photospheric temperature structure for a star like the Sun.
Including scattering in line-blanketing, however, leads to a decrease of
temperatures by about 350\,K below log tau < -4. The effect is opposite to that
of 1D hydrostatic models in radiative equilibrium, where scattering reduces the
cooling effect of strong LTE lines in the higher layers of the photosphere.
Coherent line scattering also changes the temperature distribution in the high
atmosphere, where we observe stronger fluctuations compared to a treatment of
lines as true absorbers.
