Janus: An Extensible Open-Source Software Package for Adaptive QM/MM Methods.

Adaptive quantum mechanics/molecular mechanics (QM/MM) approaches are able to treat systems with dynamic or nonlocalized active centers by allowing for on-the-fly reassignment of the QM region. Although these approaches have been in active development, the inaccessibility of current software has caused slow adoption and limited applications. Janus seeks to remedy the limitations of current software by providing a free and open-source Python library for adaptive methods that is modular and extensible. Our software has implementations of many existing adaptive methods and a user-friendly input structure that removes the hindrance of complicated setup procedures. A Python API is made available to customize Janus's capabilities and implement novel adaptive approaches. Janus currently interfaces with Psi4 and OpenMM, but its modular infrastructure enables easy extensibility to other molecular codes without major modifications to either code. The software is freely available at https://github.com/CCQC/janus . Our goal is that Janus will serve as a user-driven platform for adaptive QM/MM methods.