Coupled cluster theory for quantum many-body systems at finite temperature

Coupled cluster theory is the one of the most accurate methods for detg. the electronic structure of medium-sized systems. Underlying this accuracy is a wavefunction ansatz which provides an app. for efficient re-summation of perturbation theory diagrams. We show how an analogous app. can be constructed for many-fermion systems at finite temp. using imaginary time integration. This novel formulation of coupled cluster theory offers a powerful hierarchy of approxns. for direct computation of the observables of quantum systems at finite temp. In this talk I will discuss the theory and some progress towards ab initio simulation of fermionic systems. Applications to some model problems and extensions to non-equil. systems will also be discussed