arXiv subjects

Leo Stoll

Publications and source records attributed to Leo Stoll.

3 recordsLinked to original sources

arXiv2026

Resolving the ground state intersection problem in coupled cluster theory

A physically correct description of ground state conical intersections is essential for simulating non-adiabatic dynamics of radiationless decay to the electronic ground state. Coupled cluster theory offers a particularly balanced treatment of static and dynamic correlation in excited states. However, coupled cluster methods and other single-reference approaches fail to describe ground state intersection regions, and several workarounds have been proposed to address this shortcoming. Here we present convex similarity constrained coupled cluster theory (CVX-SCC), a framework that resolves the ground state intersection problem by construction. We have applied this theory to two different coupled cluster methods, and tested the resulting models on ethylene, uracil, PSB3, and HeH$_2$, showing that both variants produce physically correct ground state conical intersections. With future development of nuclear gradients and non-adiabatic coupling vectors, this approach will provide single-reference electronic structures suitable for non-adiabatic dynamics simulations all the way to the ground state.

physics.chem-ph↗

arXiv2025

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

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.

physics.chem-ph↗

arXiv2025

Similarity Constrained CC2 for Efficient Coupled Cluster Nonadiabatic Dynamics

Despite their high accuracy, standard coupled cluster models cannot be used for nonadiabatic molecular dynamics simulations because they yield unphysical complex excitation energies at conical intersections between same-symmetry excited states. On the other hand, similarity constrained coupled cluster theory has enabled the application of coupled cluster theory in such dynamics simulations. Here, we present a similarity constrained perturbative doubles (SCC2) model with same-symmetry excited-state conical intersections that exhibit correct topography, topology, and real excitation energies. This is achieved while retaining the favorable computational scaling of the standard CC2 model. We illustrate the model for conical intersections in hypofluorous acid and thymine, and compare its performance with other methods. The results demonstrate that conical intersections between excited states can be described correctly and efficiently at the SCC2 level. We therefore expect that the SCC2 model will enable coupled cluster nonadiabatic dynamics simulations for large molecular systems.

physics.chem-ph↗