Top panel: calculated and observed intensity profiles of the Si i 10 827 Å line corresponding to the disk-center. Solid red and dashed-dotted black lines: spatially averaged NLTE profiles calculated in the 3D MHD snapshot, respectively, with a scaling factor S_H = 0.1 and S_H = 1. Thin solid line: the LTE profile. Small open blue circles: the observed profile from the FTS atlas (Neckel & Labs 1984; Neckel 1999). Bottom panel: differences between the synthetic and the observed profiles. The NLTE profiles are calculated using the simplest Si i model with six bb transitions (see Fig. 4, bottom right panel).