New capabilities of the gmx2qmmm software

We present an update to the hybrid quantum mechanics/molecular mechanics (QM/MM) interface “gmx2qmmm”. Version 2.0 of the software is now capable of interfacing between the more recent versions of the MM package Gromacs and various other QM packages, in addition to the previously supported Gaussian16. The additional QM packages are ORCA, Turbomole and Serenity; especially the latter drastically increases the potential for QM/MM with extensively large QM regions. While the implementation of the QM packages was for most cases analogous to Gaussian, updating the compatibility to recent Gromacs versions required omission of large parts of the system, which was previously done via the now deprecated energy group exclusion scheme. The new version, gmx2qmmm 2.0, explicitly removes any surplus atoms or point charges that are not affecting the potential of any unrestrained atom (active region). It is thus more consis- tent with previous QM/MM publications, which often reduce the computational workload by deleting all but the necessary parts of the solvent shell. We fur- ther introduced numerical normal mode analyses and a linear coordinate scan function to facilitate basic potential energy surface studies, both for electronic ground and excited states.