Structure of the automorphism group for partially commutative class two nilpotent groups

Let $R$ be a ring, which is either a ring of integers or a field of zero characteristic. For every finite graph $\Gamma$, we construct an $R$-arithmetic linear group $H(\Gamma)$. The group $H(\Gamma)$ is realized as the factor automorphism group of a partially commutative class two nilpotent $R$-group $G_\Gamma$. Also we describe the structure of the entire automorphism group of a partially commutative nilpotent $R$-group of class two.