  Three-dimensional radiation-hydrodynamics (3D RHD) simulations of stellar
surface convection provide valuable insights into many problems in solar and
stellar physics. However, almost all 3D near-surface convection simulations to
date are based on solar-scaled chemical compositions, which limit their
application on stars with peculiar abundance patterns. To overcome this
difficulty, we implement the robust and widely-used FreeEOS equation of state
and our Blue opacity package into the Stagger 3D radiation-magnetohydrodynamics
code. We present a new 3D RHD model of the solar atmosphere, and demonstrate
that the mean stratification as well as the distributions of key physical
quantities are in good agreement with those of the latest Stagger solar model
atmosphere. The new model is further validated by comparing against solar
observations. The new model atmospheres reproduce the observed flux spectrum,
continuum centre-to-limb variation, and hydrogen line profiles at a
satisfactory level, thereby confirming the realism of the model and the
underlying input physics. These implementations open the prospect for studying
other stars with different $\alpha$-element abundance, carbon-enhanced
metal-poor stars and population II stars with peculiar chemical compositions
using 3D Stagger model atmospheres.
