Expanding the Range of Force Fields Available for ONIOM Calculations: The SICTWO Interface.

The ONIOM scheme is one of the most popular QM/MM approaches, but its extended application has been so far hindered by the limited availability of force fields in most practical implementations. This paper describes a simple software code to overcome this limitation, and its application to three representative chemical problems. The "Shell Interface for Combining Tinker With ONIOM" (SICTWO) program gives access to all force fields available in the Tinker molecular mechanics program from a Gaussian09 or Gaussian16 calculation. The first application presented is the geometry optimization of dithienobicyclo-[4.4.1]-undeca-3,8-diene-11-one ethylene glycol ketal. A variety of force fields were tested for the MM part, and the molecular structure using the ONIOM(B3LYP:OPLS-AA) method shows good agreement with the experimental results. The second problem is related with enantioselectivity of the vanadium-catalyzed asymmetric oxidation of 1,2-bis( tert-butyl)-disulfide. ONIOM(B3LYP:MM3) results, obtained with SICTWO, are consistent with those of a previous IMOMM(B3LYP:MM3) study. In the third application, we have combined AMOEBA09 polarizable force field with ONIOM to study a water molecule binding on water ice. Calculated ONIOM(ωB97X-D:AMOEBA09) binding energies are consistent with the ωB97X-D results. These studies show SICTWO as an easy-to-use tool that can further expand the use of the multiscale ONIOM method within computational chemistry and computational biology.