What is the meaning of the graph energy after all?

Ernesto Estrada, Michele Benzi

For a simple graph $G=(V,E)$ with eigenvalues of the adjacency matrix ${\lambda }_1\ge {\lambda }_2\ge \cdots \ge {\lambda }_n$, the energy of the graph is defined by $E(G)={\sum }_{j=1}^n|{\lambda }_j|$. Myria…