Coupled cluster description of field theories: Procedures and their application to the vacuum sector in (1+1)-dimensional ${\Phi }^4$ field theories

General procedures for the application of the nonperturbative coupled cluster method (CCM) are described for one-component boson field theories. The basis set is optimized first by a Hartree-Bogolubov transformation. Then ‘‘correlations’’ are added via the CCM. This procedure is applied to two-dimensional ${\Phi }^4$ field theory. The results are very stable outside the critical region.