hoomd.md¶
Details
Molecular dynamics.
In molecular dynamics simulations, HOOMD-blue numerically integrates the degrees
of freedom in the system as a function of time under the influence of forces. To
perform MD simulations, assign a MD Integrator
to the hoomd.Simulation
operations. Provide the Integrator
with lists of integration methods, forces,
and constraints to apply during the integration. Use hoomd.md.minimize.FIRE
to perform energy minimization.
MD updaters (hoomd.md.update
) perform additional operations during the
simulation, including rotational diffusion and establishing shear flow.
Use MD computes (hoomd.md.compute
) to compute the thermodynamic properties of
the system state.
See also
Tutorial: Introducing Molecular Dynamics
- class hoomd.md.HalfStepHook(*args: Any, **kwargs: Any)¶
HalfStepHook base class.
HalfStepHook provides an interface to perform computations during the half-step of a hoomd.md.Integrator.
- update(timestep)¶
Called during the half-step of a
hoomd.md.Integrator
.This method should provide the implementation of any computation that the user wants to execute at each timestep in the middle of the integration routine.
- class hoomd.md.Integrator(dt, integrate_rotational_dof=False, forces=None, constraints=None, methods=None, rigid=None, half_step_hook=None)¶
Molecular dynamics time integration.
- Parameters:
dt (float) – Integrator time step size \([\mathrm{time}]\).
methods (Sequence[hoomd.md.methods.Method]) – Sequence of integration methods. The default value of
None
initializes an empty list.forces (Sequence[hoomd.md.force.Force]) – Sequence of forces applied to the particles in the system. The default value of
None
initializes an empty list.integrate_rotational_dof (bool) – When True, integrate rotational degrees of freedom.
constraints (Sequence[hoomd.md.constrain.Constraint]) – Sequence of constraint forces applied to the particles in the system. The default value of
None
initializes an empty list. Rigid body objects (i.e.hoomd.md.constrain.Rigid
) are not allowed in the list.rigid (hoomd.md.constrain.Rigid) – An object defining the rigid bodies in the simulation.
half_step_hook (hoomd.md.HalfStepHook) – Enables the user to perform arbitrary computations during the half-step of the integration.
Integrator
is the top level class that orchestrates the time integration step in molecular dynamics simulations. The integrationmethods
define the equations of motion to integrate under the influence of the givenforces
andconstraints
.Each method applies the given equations of motion to a subset of particles in the simulation state. See the documentation for each method for details on what equations of motion it solves. The intersection of the subsets must be null.
Integrator
computes the net force, torque, energy, and virial on each particle as a sum of those applied byhoomd.md.force.Force
objects in theforces
andconstraints
lists:\[\begin{split}\vec{F}_{\mathrm{net},i} &= \sum_{f \in \mathrm{forces}} \vec{F}_i^f \\ \vec{\tau}_{\mathrm{net},i} &= \sum_{f \in \mathrm{forces}} \vec{\tau}_i^f \\ U_{\mathrm{net},i} &= \sum_{f \in \mathrm{forces}} U_i^f \\ W_{\mathrm{net},i} &= \sum_{f \in \mathrm{forces}} W_i^f \\\end{split}\]Integrator
also computes the net additional energy and virial\[\begin{split}U_{\mathrm{net},\mathrm{additional}} &= \sum_{f \in \mathrm{forces}} U_\mathrm{additional}^f \\ W_{\mathrm{net},\mathrm{additional}} &= \sum_{f \in \mathrm{forces}} W_\mathrm{additional}^f \\\end{split}\]See
md.force.Force
for definitions of these terms. Constraints are a special type of force used to enforce specific constraints on the system state, such as distances between particles withhoomd.md.constrain.Distance
.Integrator
handles rigid bodies as a special case, as it only integrates the degrees of freedom of each body’s center of mass. Seehoomd.md.constrain.Rigid
for details.Degrees of freedom
Integrator
always integrates the translational degrees of freedom. It optionally integrates one or more rotational degrees of freedom for a given particle i when all the following conditions are met:The intergration method supports rotational degrees of freedom.
integrate_rotational_dof
isTrue
.The moment of inertia is non-zero \(I^d_i > 0\).
Each particle may have zero, one, two, or three rotational degrees of freedom.
Note
By default,
integrate_rotational_dof
isFalse
.gsd
andhoomd.Snapshot
also set particle moments of inertia to 0 by default.Classes
Classes of the following modules can be used as elements in
methods
:The classes of following modules can be used as elements in
forces
:The classes of the following module can be used as elements in
constraints
:Examples:
nlist = hoomd.md.nlist.Cell() lj = hoomd.md.pair.LJ(nlist=nlist) lj.params.default = dict(epsilon=1.0, sigma=1.0) lj.r_cut[('A', 'A')] = 2**(1/6) nve = hoomd.md.methods.NVE(filter=hoomd.filter.All()) integrator = hoomd.md.Integrator(dt=0.001, methods=[nve], forces=[lj]) sim.operations.integrator = integrator
- methods¶
List of integration methods.
- Type:
- forces¶
List of forces applied to the particles in the system.
- Type:
- constraints¶
List of constraint forces applied to the particles in the system.
- rigid¶
The rigid body definition for the simulation associated with the integrator.
- Type:
- half_step_hook¶
User defined implementation to perform computations during the half-step of the integration.
- Type:
- __setattr__(attr, value)¶
Hande group DOF update when setting integrate_rotational_dof.
Modules