Rational Calogero–Moser model: explicit form and $r$-matrix of the second Poisson structure

We compute the full expression of the second Poisson bracket structure for $N=2$ and $N=3$ site rational classical Calogero–Moser model. We propose an $r$-matrix formulation for $N=2$. It is identified with the classical limit of the second dynamical boundary algebra previously built by the authors.