When an algebra is graded
by a group, any additive character of the group induces a diagonalizable derivation of
the ring. This construction is studied in detail for the case of a path algebra
modulo relations and its fundamental group. We describe an injection of
the character group into the first cohomology group following Assem-de la
Peña. Rather general conditions are determined, in this context, which
guarantee that a diagonalizable derivation is induced from the fundamental
group.