Towards large-scale restricted active space calculations inspired by the Schmidt decomposition

TL;DR

This paper introduces a memory-efficient, Schmidt decomposition-based approach called DMRG-RAS for large-scale restricted active space calculations, showing promising results for strongly correlated molecules.

Contribution

The paper presents a novel DMRG-RAS method that integrates Schmidt decomposition with RAS, enhancing efficiency and accuracy in multi-reference quantum chemistry calculations.

Findings

Outperforms conventional methods on C₂ and Cr₂ benchmarks.

Accurately predicts ground and excited states.

Demonstrates potential for large-scale strongly correlated systems.

Abstract

We present an alternative, memory-efficient, Schmidt decomposition-based description of the inherently bipartite restricted active space (RAS) scheme, which can be implemented effortlessly within the density matrix renormalization group (DMRG) method via the dynamically extended active space procedure. Benchmark calculations are compared against state-of-the-art results of C$_2$ and Cr$_2$, which are notorious for their multi-reference character. Our results for ground and excited states together with spectroscopic constants demonstrate that the proposed novel approach, dubbed as DMRG-RAS, which is variational and free of uncontrolled method errors, has the potential to outperfom conventional methods for strongly correlated molecules.