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A previous shell-model-style calculation for the ground-state energy of the 'He nucleus, based on coupled cluster techniques, was able to treat exactly the centre-of-mass motion. It is now recast in a precisely equivalent but vastly more computationally efiaent form, directly in terms of coordinate-space correlation functions which are expanded in a Gaussian geminal basis and determined variationally. This reformulation further leads in a straightforward manner to a natural procedure for including higher-order correlations. Its implementation at even the simplest level produces a significant improvement in the already very good upper bounds achieved far the ground-state energy. Further extensions are also discussed.

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Both single-well and multiwell one-dimensional anharmonic oscillators have provided an extremely fruitful testing ground for various modern techniques of microscopic quantum many-body theory and quantum field theory. They have served both as (0+1)-dimensional field-theory models