Improving Perturbation Theory with the Sum-of-squares II: Large Density-Density Terms

Matthew B. Hastings

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arXiv · 2606.31765

Improving Perturbation Theory with the Sum-of-squares II: Large Density-Density Terms

Matthew B. Hastings

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Abstract

In Ref. 1, a method was given for self-consistently generating sum-of-squares decompositions of quartic fermionic Hamiltonians. Perturbation theory was used to generate a useful choice of cubic operators in this sum-of-squares. On a range of model problems, this method, which is only a fragment of degree-six sum-of-squares, was able to outperform the full degree-four sum-of-squares in both speed and accuracy. Unfortunately for applications, many problems in chemistry have strong density-density interaction terms, as well as moderately strong density-dependent hopping and spin-spin interaction terms, limiting the power of the perturbative choice of the cubic operators. Here we propose a method for generating these decompositions in the presence of these strong interaction terms, hopefully extending the range of applicability of this method.

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Matthew B. Hastings. 2026-06-30. Improving Perturbation Theory with the Sum-of-squares II: Large Density-Density Terms. https://arxiv.org/abs/2606.31765

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