The Normalized Revised Szeged Index

In chemical graph theory, many graph parameters, or topological indices, were proposed as estimators of molecular structural properties. Often several variants of an index are considered. The aim is to extend the original concept to larger families of graphs than initially considered, or to make it more precise and discriminant, or yet to make its range of values similar to that of another index, thus facilitating their comparison. In this paper, we introduce a new variant of the Szeged index. It is named normalized revised Szeged index, and is obtained by taking the square root of the revised Szeged index divided by the number of edges in the considered graph. The spread of its values is the same as for the Randić index. We also study the correlations between the Szeged indices, as well as the Randić index, and the boiling point of chemical graphs with up to eight vertices.