  Physically realistic models of stellar spectra are needed in a variety of
astronomical studies, from the analysis of fundamental stellar parameters, to
studies of exoplanets and stellar populations in galaxies. Here we present a
new version of the widely-used radiative transfer code Turbospectrum, which we
update with the capacity to perform spectrum synthesis for lines of multiple
chemical elements in Non-Local Thermodynamic Equilibrium (NLTE). We use the
code in the analysis of metallicites and abundances of the Gaia FGK benchmark
stars, using one-dimensional MARCS atmospheric models and the averages of 3D
radiation-hydrodynamics simulations of stellar surface convection. We show that
the new more physically realistic models offer a better description of the
observed data and make the program and the associated microphysics data
publicly available, including grids of NLTE departure coefficients for H, O,
Na, Mg, Si, Ca, Ti, Mn, Fe, Co, Ni, Sr, and Ba.
