Further results on atom-bond connectivity index of trees

Abstract: The atom-bond connectivity (ABC) index of a graph is defined as where is the edge set and is the degree of vertex of . We give the best upper bound for the ABC index of trees with a perfect matching, and characterize the unique extremal tree, which is a molecular tree. We also give upper bounds for the ABC index of trees with fixed number of vertices and maximum degree, and of molecular trees with fixed numbers of vertices and pendent vertices, and characterize the extremal trees. [Copyright &y& Elsevier]