fix_modify AtC control thermal command — LAMMPS documentation

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# fix_modify AtC control thermal command

## Syntax

    fix_modify <AtC fixID> control <physics_type> <solution_parameter> <value>
    fix_modify <AtC fixID> control thermal <control_type> <optional_args>
    fix_modify <AtC fixID> control thermal rescale <frequency>
    fix_modify <AtC fixID> control thermal flux <boundary_integration_type> <faceset_id>
    fix_modify <AtC fixID> control thermal correction_max_iterations <max_iterations>

- 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

- thermal control_type = none or rescale or hoover or flux

- frequency = time step frequency for applying velocity rescaling

- boundary_integration_type = faceset or interpolate (optional)

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

- correction_max_iterations = maximum number of iterations that will be used by iterative matrix solvers for thermal physics type

## Examples

    fix_modify AtC control thermal none
    fix_modify AtC control thermal rescale 10
    fix_modify AtC control thermal hoover
    fix_modify AtC control thermal flux
    fix_modify AtC control thermal flux faceset bndy_faces
    fix_modify AtC control thermal correction_max_iterations 10

## 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 thermal version sets the energy 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. hoover and flux allow the prescription of sources or fixed temperatures on the atoms.

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 thermal is only for be used with specific transfers: thermal (rescale, hoover, flux), two_temperature (flux). rescale not valid with time filtering activated

correction_max_iterations is only for use with thermal physics using the fractional step method.

## Related AtC commands

- fix_modify AtC command overview

- fix_modify AtC control momentum

## Default

- max_iterations is the number of rows in the matrix.

- tolerance is 1.0e-10.

- rescale frequency is 1

- flux boundary_integration_type is interpolate

- correction_max_iterations is 20