1.. index:: fix_modify AtC control momentum
2
3fix_modify AtC control momentum command
4=======================================
5
6Syntax
7""""""
8
9.. parsed-literal::
10
11   fix_modify <AtC fixID> control <physics_type> <solution_parameter> <value>
12   fix_modify AtC control momentum none
13   fix_modify AtC control momentum rescale <frequency>
14   fix_modify AtC control momentum glc_displacement
15   fix_modify AtC control momentum glc_velocity
16   fix_modify AtC control momentum hoover
17   fix_modify AtC control momentum flux [faceset face_set_id, interpolate]
18
19* AtC fixID = ID of :doc:`fix atc <fix_atc>` instance
20* control = name of the AtC sub-command
21* physics_type = *thermal* or *momentum*
22* solution_parameter = *max_iterations* or *tolerance*
23* value = solution_parameter value
24* momentum option = *none* or *rescale* or *glc_displacement* or *glc_velocity* *hoover* or *flux*
25* frequency = time step frequency for applying displacement and velocity rescaling
26* faceset_id = id of boundary face set (optional, only for *faceset*)
27
28
29Examples
30""""""""
31
32.. code-block:: LAMMPS
33
34   fix_modify AtC control momentum none
35   fix_modify AtC control momentum flux faceset bndy_faces
36   fix_modify AtC control momentum glc_velocity
37
38Description
39"""""""""""
40
41The general version of *control* sets the numerical parameters for the
42matrix solvers used in the specified control algorithm.  Many solution
43approaches require iterative solvers, and these methods enable users to
44provide the maximum number of iterations and the relative tolerance.
45
46The *control momentum* version sets the momentum exchange mechanism from
47the finite elements to the atoms, managed through a control algorithm.
48*rescale* computes a scale factor for each atom to match the finite
49element temperature.  *hoover* is a Gaussian least-constraint isokinetic
50thermostat enforces that the nodal restricted atomic temperature matches
51the finite element temperature.  *flux* is a similar mode, but rather
52adds energy to the atoms based on conservation of energy.
53
54*correction_max_iterations* sets the maximum number of iterations to
55compute the second order in time correction term for lambda with the
56fractional step method. The method uses the same tolerance as the
57controller's matrix solver.
58
59Restrictions
60""""""""""""
61
62Only for be used with the specific controllers *thermal* or *momentum*.
63They are ignored if a lumped solution is requested.
64
65*control momentum* is only for be used with specific transfers: elastic
66*rescale* not valid with time filtering activated
67
68Related AtC commands
69""""""""""""""""""""
70
71- :ref:`fix_modify AtC command overview <atc_fix_modify>`
72- :doc:`fix_modify AtC control thermal <atc_control_thermal>`
73
74Default
75"""""""
76
77- *max_iterations* is the number of rows in the matrix.
78- *tolerance* is 1.0e-10.
79