fix_modify AtC control momentum command — LAMMPS documentation

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# fix_modify AtC control momentum command

## Syntax

    fix_modify <AtC fixID> control <physics_type> <solution_parameter> <value>
    fix_modify AtC control momentum none
    fix_modify AtC control momentum rescale <frequency>
    fix_modify AtC control momentum glc_displacement
    fix_modify AtC control momentum glc_velocity
    fix_modify AtC control momentum hoover
    fix_modify AtC control momentum flux [faceset face_set_id, interpolate]

- AtC fixID = ID of fix atc instance

- control = name of the AtC sub-command

- physics_type = thermal or momentum

- solution_parameter = max_iterations or tolerance

- value = solution_parameter value

- momentum option = none or rescale or glc_displacement or glc_velocity hoover or flux

- frequency = time step frequency for applying displacement and velocity rescaling

- faceset_id = id of boundary face set (optional, only for faceset)

## Examples

    fix_modify AtC control momentum none
    fix_modify AtC control momentum flux faceset bndy_faces
    fix_modify AtC control momentum glc_velocity

## Description

The general version of control sets the numerical parameters for the matrix solvers used in the specified control algorithm. Many solution approaches require iterative solvers, and these methods enable users to provide the maximum number of iterations and the relative tolerance.

The control momentum version sets the momentum exchange mechanism from the finite elements to the atoms, managed through a control algorithm. rescale computes a scale factor for each atom to match the finite element temperature. hoover is a Gaussian least-constraint isokinetic thermostat enforces that the nodal restricted atomic temperature matches the finite element temperature. flux is a similar mode, but rather adds energy to the atoms based on conservation of energy.

correction_max_iterations sets the maximum number of iterations to compute the second order in time correction term for lambda with the fractional step method. The method uses the same tolerance as the controller’s matrix solver.

## Restrictions

Only for be used with the specific controllers thermal or momentum. They are ignored if a lumped solution is requested.

control momentum is only for be used with specific transfers: elastic rescale not valid with time filtering activated

## Related AtC commands

- fix_modify AtC command overview

- fix_modify AtC control thermal

## Default

- max_iterations is the number of rows in the matrix.

- tolerance is 1.0e-10.