IMD

Interactions

IMD supports a large variety of different (mostly short range) effective potentials. Some of these potentials are defined by tabulated functions read from a potential file, others are defined analytically by parameters read from the parameter file. The potentials supported include central pair potentials, Embedded Atom Method (EAM) potentials for metals, Modified EAM (MEAM) potentials, different covalent potentials, notably Tersoff, Stillinger-Weber (analytic and tabulated), Zhou-Wadley (analytic and tabulated), and Keating potentials, Coulomb and shell model potentials for ionic solids, and Gay-Berne potentials for nematic liquid crystals.

Since the computation of the forces is the most time-critical part of a molecular dynamics simulation, support for each type of interaction has to be enabled explicitly by a compilation option. If no interaction type is specified, central pair potentials are assumed by default. Different interaction types can be combined with each other, by enabling more than one type of interaction. Their contributions are then just added. This is still somewhat experimental, and there are some restrictions. Here are some guidelines:

At most one of the covalent potentials (including MEAM, which is algorithmically similar) can be used at a time.
Central pair potentials, EAM potentials, and one of Tersoff or Stillinger-Weber potentials (tabulated or analytic) can be combined with each other. The central pair potential part contained in these interactions is shared.
The option pair can be used to enable a (short range) pair potential part together with Coulomb potentials. The same option is also used to enable the harmonic potential used for the shell model in combination with Coulomb interactions.
Coulomb potentials can be combined with almost everything else, whether or not this makes sense.
Keating and Gay-Berne potentials cannot be combined with anything else.
On vector machines, add the option "lj" for computed Lennard-Jones interactions.