  We develop an energy-based finite difference method for the wave equation in
second order form. The spatial discretization satisfies a summation-by-parts
(SBP) property. With boundary conditions and material interface conditions
imposed weakly by the simultaneous-approximation-term (SAT) method, we derive
energy estimates for the semi-discretization. In addition, error estimates are
derived by the normal mode analysis. The energy-based discretization does not
use any mesh-dependent parameter, even in the presence of Dirichlet boundary
conditions and material interfaces. Furthermore, similar to upwind
discontinuous Galerkin methods, numerical dissipation can be added to the
discretization through the boundary conditions. We present numerical
experiments that verify convergence and robustness of the proposed method.
