On Second Geometric-Arithmetic Index and Co-PI Index of Special Chemical Molecular Structures

Abstract. In theoretical chemistry, chemical compounds and dr ugs are modelled as graphs, and the second geometric-arithmetic index and Co-PI index have been introduced to measure the stability of alkanes and the strain ene rgy of cycloalkanes. These indices have found several applications in QSPR/QSAR study, and lso used to test the toxicity of drugs. In this paper, we present the computational formulas for calculating the second geometric-arithmetic index and Co-PI index of unila ter l polyomino chain, unilateral hexagonal chain, V-phenylenic nanotubes and nanotor i, and hexagonal triangle graph. In addition, the general second geometric-arithmetic i ndex and general Co-PI index are defined, and the representations of special chemica l olecular graphs in general version are derived.