An application

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The following figure shows the errors of various methods with respect to full CI in a logarithmic scale for the Li₂ molecule:

Single-reference coupled-cluster performs very well close to the equilibrium geometry but deteriorates significantly approaching the multi-reference dissociation limit. The SS-MRCC approach of Mahapatra et. al. [18,19] works well and shows very little variation in accuracy passing from the equilibrium to dissociation. However, the curve seems to be a bit noisy around 5, 8.5 and 12 Bohr coinciding with potential intruder states. In contrast to this the error of the inherently symmetry broken SR-MRCC [20,21] and MRexpT [15] calculations behaves very smooth across the whole surface although the overall error variation is higher since the approaches become very accurate for large distances. Interestingly the error of the MRexpT results is framed by the SR-MRCC approaches along the surface. There are further applications of MRexpT in the literature [15,16] and more to come.