  We investigate the accuracy of a number of wavefunction based methods at the
heart of quantum chemistry for metallic systems. Using Hartree-Fock as a
reference, perturbative (M{\o}ller-Plesset, MP) and coupled cluster (CC)
theories are used to study the uniform electron gas model. Our findings suggest
that non-perturbative coupled cluster theories are acceptable for modelling
electronic interactions in metals whilst perturbative coupled cluster theories
are not. Using screened interactions, we propose a simple modification to the
widely-used coupled-cluster singles and doubles plus perturbative triples
method (CCSD(T)) that lifts the divergent behaviour and is shown to give very
accurate correlation energies for the homogeneous electron gas.
