Penguin: A Python-Based Program for Electronic Structure Calculations Based on Coupled Cluster Theory

The Penguin program is an open-source Python program that enables molecular property and spectroscopy calculations using coupled cluster theory and perturbation theory approaches, such as cluster perturbation theory and Mo̷ller-Plesset perturbation theory. This is the first time that cluster perturbation theory approaches have been made available in open source software. The program is written in a modular and object-oriented fashion and features a matrix element library for evaluating commonly encountered terms in coupled cluster theory. The Penguin program supports interactive usage through Jupyter notebooks, making it ideal for educational purposes as well as rapid prototyping of novel coupled cluster and perturbation theory methods. In the current version, the program also features an OpenMP/MPI parallel version of the CC2 model highlighting the high performance computing potential that can be realized using this strategy of software design.