Energy ordering of catacondensed hexagonal systems
The energy of a graph G G is defined as E ( G ) = ? i = 1 n | ? i | , where ?i ? i (i=1,,n i = 1 ,  , n ) are the eigenvalues of G G . In this work we define the coalescence of two graphs with respect to (oriented) edges, and show that for the graphs X X and Y Y in Fig. 2, which are obtained by coalescence of bipartite graphs around the six-vertex cycle C6 C 6 , E(X)?E(Y) E ( X ) ? E ( Y ) . As a by-product, we give energy ordering relations in the class of catacondensed hexagonal systems.
energy hexagonal systems cycles catacondensed systems hexagonal chains quasi-order