Solvents, proteins, and other environments

You can study chemistry in solution with the implementation in ADF of the conductor like screening model (COSMO) of solvation, see also more COSMO details.

For truly large system sizes (thousands of atoms), a mix of quantum mechanics and molecular mechanics (QM/MM) is often suitable if the major quantum effects are restricted to a certain part of the molecule ('active site'). QM/MM calculations can be performed on much larger systems than pure QM calculations, because the approximate MM calculations are very fast. Various standard force fields (SYBYL, Amber) are available.

The Discrete Reaction Field (DRF) model enables QM/MM calculation with polarizable MM atoms.
The frozen density embedding (FDE) method is a mixture of Kohn-Sham DFT with DFT that depends purely on the density (DFT/DFT).
The QUILD program has been developed for enabling calculations through multi-level (QM/QM or QM/MM) approaches.

In ADF one can of corse also specify a homogeneous electric field and point charges.

Links

ADF User Documentation: COSMO, QM/MM, DRF, FDE, Quild
ADF-GUI: model Hamiltonians, Tutorial: QM/MM
Examples: solvents and other environments, QM/MM, Quild

With the controls in the ADFinput module you can select which atoms to put in the QM and MM region (visualization with ADFinput)