Abstract
The energy of a graph G, denoted by E(G), is the sum of the absolute
values of all eigenvalues of G. In this paper we present some lower
and upper bounds for E(G) in terms of number of vertices, number
of edges, and determinant of the adjacency matrix. Our lower bound
is better than the classical McClelland’s lower bound. In addition,
Nordhaus–Gaddum type results for E(G) are established.