molecular-dynamics.rst

Algorithms for molecular dynamics

Writing a new integrator <type-Integrator>

To create a new integrator, you have to subtype the Integrator type, and provide the call method, with the following signature: call(::Integrator, ::MolecularDynamic).

The integrator is responsible for calling the getforces!(::MolecularDynamics, ::Universe) function when the MolecularDynamics.forces field needs to be updated. It should update the two Array3D <type-Array3D>: Universe.frame.positions and Universe.frame.velocities with appropriate values.

The Universe.masses field is a Vector{Float64} containing the particles masses. Any other required information should be stored in the new Integrator subtype.

Computing the forces

To create a new force computation algorithm, you have to subtype ForcesComputer, and provide the method call(::ForcesComputer, ::Universe, forces::Array3D).

This method should fill the forces array with the forces acting on each particles: forces[i] should be the 3D vector of forces acting on the atom i. In order to do this, the algorithm can use the Universe.frame.posistions and Universe.frame.velocities arrays.

Potentials to use for the atoms can be optained throught the following functions:

pairs(::Interactions, i, j)

Get a Vector{PairPotential} of interactions betweens atoms i and j.

bonds(::Interactions, i, j)

Get a Vector{BondPotential} of interactions betweens atoms i and j.

angles(::Interactions, i, j, k)

Get a Vector{AnglePotential} of interactions betweens atoms i and j and k.

dihedrals(::Interactions, i, j, k, m)

Get a Vector{DihedralPotential} of interactions betweens atoms i, j, k and m.

Adding new checks <type-check>

Adding a new check algorithm is as simple as subtyping Check and extending the call(::Check, ::Universe, ::MolecularDynamic) method. This method should throw an exception of type CheckError if the checked condition is not fullfiled.

Adding new controls <type-control>

To add a new type of control to a simulation, the main way is to subtype Control, and provide two specialised methods: call(::Control, ::Universe) and the optional setup(::Control, ::Simulation). The call method should contain the algorithm inplementation, and the setup method is called once at each simulation start. It should be used to add add some computation algorithm <type-compute> to the simulation, as needed.