Bootstrap Embedding For Large Molecular Systems

Recent
developments in quantum embedding theories have provided
attractive approaches to correlated calculations for large systems.
In this work, we extend our previous work [J. Chem. Theory
Comput. 2019, 15, 4497–4506; J. Phys. Chem. Lett. 2019, 10, 6368–6374] on bootstrap embedding (BE) to enable correlated
ab initio calculations at the coupled cluster with singles and doubles
(CCSD) level for large molecules. We introduce several new algorithmic
developments that significantly
reduce the computational cost of BE, while maintaining its accuracy.
The resulting implementation scales as O(N3) for the integral transform and O(N) for the CCSD calculation. Numerical results
on a series of conjugated molecules suggest that BE with reasonably
sized fragments can recover more than 99.5% of the total correlation
energy of a full CCSD calculation, while the required computational
resources (time and storage) compare favorably to one popular local
correlation scheme: domain localized pair natural orbital (DLPNO).
The largest BE calculation in this work involves ∼2900 basis
functions and can be performed on a single node with 16 CPU cores
and 64 GB of memory in a few days. We anticipate that these developments
represent an important step toward the application of BE to solve
practical problems.