1. The Designer Challenge While the mission of the 20th century was related to providing answers to question pertaining to properties of specific chemical structures, the questions of the 21st century revolves around the inverse design problem -finding the best chemical structures that are associated with desired and requested properties. A potential solution for this challenge is the use of invertible models from machine learning such as generative models (GANs, autoencoders, …) or inverting molecules from families of Hamiltonians .