Quantum Chemistry-Driven Molecular Inverse Design of Stable Isomers with Data-Free Reinforcement Learning

The inverse design (ID) of molecules remains one of the greatest challenges in chemistry. Machine learning and artificial intelligence (AI) methods are increasingly employed to generate candidate molecules with tailored properties but mostly rely on pretraining over large data sets, which introduces bias. Here, we present a data-free generative AI model called PROTEUS that integrates reinforcement learning with on-the-fly quantum mechanical calculations to enable the de novo design of molecules from first-principles. The AI tool uses a custom syntax and hierarchical learning architecture to navigate the chemical space without prior knowledge, optimizing the desired chemical property. We demonstrate the efficiency of our software by solving complex molecular design tasks related to the maximization of isomerization energy gaps for styrene derivatives. By solving ID problems for which the exact solutions are known, PROTEUS proved to be robust and flexible enough to perform a broad exploration of different chemical spaces while successfully exploiting chemical rewards. This framework opens new avenues for quantum chemistry-driven unbiased molecular design, offering a flexible and scalable strategy to address design challenges in chemistry.