A bit over a year ago we published our adcc code. In this work the aim was to develop a toolkit for computational spectroscopy methods focused on rapid development and interactive hands-on usage (see the blog article for details). Our target back then was to simplify method development involving the algebraic-diagrammatic construction approach (ADC) to compute excited states energies and properties. ADC has been a research focus both of myself as well as the group of Andreas Dreuw and the ADC family of methods have proven in the past to be greatly suited for describing photochemistry and spectroscopic results.

Employing mainly thread-based parallelism and (apart from our recent inclusion of libxm) basically no options for swapping stored tensors to disk, adcc is naturally restricted to problems that fit into the main memory of a single cluster node. This is fine for developing and testing new ADC methods, but can be limiting for employing ADC methods in practice: The code can currently only treat small-sized to medium-sized molecules.

In parallel to adcc we therefore started working on the Gator project in collaboration with the groups of Patrick Norman and Zilvinas Rinkevicius (both KTH Stockholm). We now release in a first version. Apart from an interface to adcc, Gator features a response library capable of the complex polarisation propagator (CPP) approach for simulating properties such as excited-states polarisabilities or enabling a direct computation of spectra including broadening. Additionally it contains a newly developed ADC(2) module with MPI-based distributed computing capabilities. For this the integral driver of the Veloxchem code from KTH is used, which allows the ADC(2) computation to be performed in a direct fashion (i.e. without storing the two-electron-integral tensor). This makes ADC(2) simulations in Gator more memory efficient and allows them to be distributed over a few cluster nodes. In this publication we provide an overview of Gator's current capabilities. The full abstract reads

The Gator program has been developed for computational spectroscopy and calculations of molecular properties using real and complex propagators at the correlated level of wave function theory. At present, the focus lies on methods based on the algebraic diagrammatic construction (ADC) scheme up to third-order of perturbation theory. A Fock matrix-driven implementation of the second-order ADC method for excitation energies has been realized with an underlying hybrid MPI/OpenMP parallelization scheme suitable for execution in high-performance computing cluster environments. With a modular and object-oriented program structure written in a Python/C++ layered fashion, Gator enables, in addition, time-efficient prototyping of novel scientific approaches as well as interactive notebook-driven training of students in quantum chemistry.

Article
Dirk R. Rehn, Zilvinas Rinkevicius, Michael F. Herbst and others. Gator: a Python-driven program for spectroscopy simulations using correlated wave functions. WIREs Computational Molecular Science, 11, e1528 (2021). DOI 10.1002/wcms.1528 [code]