eT 2.0: An efficient open-source molecular electronic structure program

TL;DR

eT 2.0 is an open-source electronic structure software that enhances performance, supports diverse models including coupled cluster and DFT, and introduces new features for strong light-matter interactions and spectroscopic simulations.

Contribution

The paper introduces eT 2.0, a major update with optimized algorithms, new capabilities for energy surface exploration, and specialized functions for strong light-matter coupling.

Findings

eT 2.0 outperforms previous versions and other programs in coupled cluster calculations.

New features enable efficient exploration of potential energy surfaces.

Spectroscopic simulations are more accurate and computationally efficient.

Abstract

The eT program is an open-source electronic structure program with emphasis on performance and modularity. As its name suggests, the program features extensive coupled cluster capabilities, performing well compared to other electronic structure programs, and, in some cases, outperforming commercial alternatives. However, eT is more than a coupled cluster program; other models based on wave function theory (such as full and reduced space configuration interaction and a variety of self-consistent field models) and density functional theory are supported. The second major release of the program, eT 2.0, has specialized functionality for strong light-matter coupling conditions. In addition, it includes a wide range of optimizations and algorithmic improvements, as well as new capabilities for exploring potential energy surfaces and for modeling experiments in the UV and X-ray regimes. Molecular gradients are now available at the coupled cluster level, and high-accuracy spectroscopic simulations are available at reduced computational cost within the multilevel coupled cluster and multiscale frameworks. We present the modifications to the program since its first major release, eT 1.0, highlighting some notable new features and demonstrating the performance of the new version relative to the first release and to other established electronic structure programs.