Molecular Mechanics Interfaces
ChemShell provides number of molecular mechanics interfaces, capable
to generating energy and gradients for use in the ChemShell geometry
optimisation and MD drivers. In general, the dynamics options of these
codes are not available through ChemShell (see the Dynamics section).
These interfaces are not standardised in the way the quantum mechanics
interfaces are, and they use quite different programming models and
have different capabilities
- DL_POLY and GULP are built into ChemShell binary (in the GULP case,
not by default). The CHARMM interface uses the standard distribution
version of CHARMM and runs it a separate process, communicating by
name pipes.
- The DL_POLY interface is adapted to work as a part of QM/MM
calculations. The GULP and CHARMM interfaces are, in general, not
(although some support is provided). If you use GULP or CHARMM in
a QM/MM context you will need to check carefully that your forcefield
input generates the correct energy expression for the QM region. This
can often be achieved by defining a range of atom types and custom
topologies. CHARMM topologies can be read into the DL_POLY interfaces, which is
the recommended way or performing QM/MM simulations with the CHARMM forcefield.
In general, therefore it will not be possible to switch the MM
code specification in a ChemShell script without checking the details.
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