Faces of maximal chain polytopes

The maximal chain polytope $\mathscr{M}(P)$ is associated with a finite poset $P$. For a set of maximal chains $\mathcal{C}$, it is shown that the convex hull of all the points corresponding to elements of $\mathcal{C}$ is not a face of $\mathscr{M}(P)$ if and only if $\mathcal{C}$ has an incomplete guided crown structure. Using this result, several examples, including the dimension of $\mathscr{M}(\boldsymbol{m} \times \boldsymbol{n})$, are calculated.