Reduced Scaling Electronic Structure Methods in CFOUR: Theory, Implementation, and Open-Source Software Components

Wavefunction methods such as coupled-cluster and many-body perturbation methods provide accurate electronic properties but suffer from steep polynomial scaling. Cholesky decomposition/resolution-of-the-identity, the canonical polyadic decomposition, rank-reduced coupled cluster, and tensor hypercontraction are some examples of successful approaches which reduce the order of polynomial scaling without losing significant accuracy. Our group has been particularly working towards implementing higher-order rank-reduced as well as grid-based least-squares tensor hypercontraction electronic structure methods within the CFOUR program system. An effective implementation of such methods relies on many complex and inter-related software components such as generation and manipulation of molecular grids, rapid generation of electron repulsion integrals (especially on accelerators), as well as tensor contraction, hyper-contraction, and related linear algebra operations in a variety of precisions and mathematical domains. In this talk we provide an overview of the methods themselves, their implementation in CFOUR, and the reusable and open-source software components which we have developed.