Active space decomposition with multiple sites: Density matrix renormalization group algorithm

TL;DR

This paper extends the active space decomposition method to multiple sites using DMRG, enabling highly accurate calculations of large molecular systems by efficiently handling interfragment electron correlation.

Contribution

We develop a multi-site active space decomposition method with DMRG, achieving rapid convergence and near-exact results for complex molecular systems.

Findings

Truncation errors decrease exponentially with the number of renormalization states M.

Numerically exact calculations are possible with M=128.

The method effectively captures interfragment electron correlation.

Abstract

We extend the active space decomposition method, recently developed by us, to more than two active sites using the density matrix renormalization group algorithm. The fragment wave functions are described by complete or restricted active-space wave functions. Numerical results are shown on a benzene pentamer and a perylene diimide trimer. It is found that the truncation errors in our method decrease almost exponentially with respect to the number of renormalization states M, allowing for numerically exact calculations (to a few microhartrees or less) with M = 128 in both cases. This rapid convergence is because the renormalization steps are used only for the interfragment electron correlation.