  We consider a system of weakly coupled singularly perturbed semilinear
elliptic equations. First, we obtain a Lipschitz regularity result for the
associated ground energy function $\Sigma$ as well as representation formulas
for the left and the right derivatives. Then, we show that the concentration
points of the solutions locate close to the critical points of $\Sigma$ in the
sense of subdifferential calculus.
