Non-perturbative effective QCD Hamiltonian

A non-relativistic approximation to quantum chromodynamics is used and nonperturbative properties of the vacuum are parameterized by the gluon condensate. We calculate non-perturbative contributions in mesons by extending the basis to also include singlet states formed by octet quark-antiquark states coupled to the background fields. We thereby calculate masses and wave functions of pseudoscalar heavy mesons. Non-perturbative effects are shown to be more important in higher excited states. The background gauge formalism used preserves gauge invariance. (author)