Complex sentence: Green's functions are also a useful tool in solving wave equations, diffusion equations, and in quantum mechanics, where the Green's function of the Hamiltonian is a key concept, with important links to the concept of density of states.
Split into simpler sentences: Green's functions are also a useful tool in solving wave equations and diffusion equations. In quantum mechanics, the Green's function of the Hamiltonian is a key concept with important links to the concept of density of states.