We give a complete list of smooth and rationally smooth normalized Schubert varieties in the twisted affine Grassmannian associated with a tamely ramified group and a special vertex of its Bruhat–Tits building. The particular case of the quasi-minuscule Schubert variety in the quasi-split but non-split form of (ramified triality) provides an input needed in the article by He–Pappas–Rapoport classifying Shimura varieties with good or semi-stable reduction.
"Smoothness of Schubert varieties in twisted affine Grassmannians." Duke Math. J. 169 (17) 3223 - 3260, 15 November 2020. https://doi.org/10.1215/00127094-2020-0025