.. index:: compute temp/deform
.. index:: compute temp/deform/kk

compute temp/deform command
===========================

Accelerator Variants: *temp/deform/kk*

Syntax
""""""

.. code-block:: LAMMPS

   compute ID group-ID temp/deform keyword value ...

* ID, group-ID are documented in :doc:`compute <compute>` command
* temp/deform = style name of this compute command
* zero or more keyword/value pairs may be appended
* keyword = *temp*

  .. parsed-literal::

     *temp* value = compute ID that calculates a temperature

Examples
""""""""

.. code-block:: LAMMPS

   compute myTemp all temp/deform

Description
"""""""""""

Define a computation that calculates the temperature of a group of
atoms, after subtracting out a streaming velocity induced by the
simulation box changing size and/or shape, for example in a
non-equilibrium MD (NEMD) simulation.  The size/shape change is
induced by use of the :doc:`fix deform <fix_deform>` command.  A compute
of this style is created by the :doc:`fix nvt/sllod <fix_nvt_sllod>`
command to compute the thermal temperature of atoms for thermostatting
purposes.  A compute of this style can also be used by any command
that computes a temperature (e.g., :doc:`thermo_modify <thermo_modify>`,
:doc:`fix temp/rescale <fix_temp_rescale>`, :doc:`fix npt <fix_nh>`).

The deformation fix changes the box size and/or shape over time, so
each atom in the simulation box can be thought of as having a
"streaming" velocity.  For example, if the box is being sheared in *x*,
relative to *y*, then atoms at the bottom of the box (low *y*) have a
small *x* velocity, while atoms at the top of the box (high *y*) have a
large *x* velocity.  This position-dependent streaming velocity is
subtracted from each atom's actual velocity to yield a thermal
velocity, which is then used to compute the temperature.

.. versionchanged:: 11Feb2026

The method for calculating temperature once the streaming velocity
has been removed depends on the internal temperature compute.
By default if the *temp* keyword is omitted,
:doc:`compute temp <compute_temp>` is used, and the internal
temperature compute is created automatically as if the following command
had been issued:

.. code-block:: LAMMPS

   compute compute-ID_temp group-ID temp

The *temp* keyword allows an alternative internal temperature compute to be
specified.  For example, this can be used to exclude some directions with
:doc:`compute temp/partial <compute_temp_partial>`, or account for
additional bias beyond that due to deformation by using
:doc:`compute temp/profile <compute_temp_profile>`.  The group ID of
compute temp/deform and the internal temperature compute must match.
The internal temperature compute can be changed with the
:doc:`compute_modify <compute_modify>` command.

.. note::

   If the internal temperature compute is evaluated directly,
   e.g. with "c_compute-ID_temp" or "c_compute-ID_temp[*]", then
   the streaming component of the velocity will NOT be removed for
   that calculation.

.. note::

   :doc:`Fix deform <fix_deform>` has an option for remapping either
   atom coordinates or velocities to the changing simulation box.  When
   using this compute in conjunction with a deforming box, fix deform
   should NOT remap atom positions, but rather should let atoms respond
   to the changing box by adjusting their own velocities (or let
   :doc:`fix deform <fix_deform>` remap the atom velocities; see its remap
   option).  If fix deform does remap atom positions, then they appear to
   move with the box but their velocity is not changed, and thus they do
   NOT have the streaming velocity assumed by this compute.  LAMMPS will
   warn you if fix deform is defined and its remap setting is not
   consistent with this compute.  A similar situation arises if
   :doc:`fix nvt/sllod <fix_nvt_sllod>` is used with the "peculiar yes"
   option.

After the streaming velocity has been subtracted from each atom,
the temperature is calculated as specified by the internal temperature
compute.  With :doc:`compute temp <compute_temp>` as the internal temperature
compute (the default), the temperature is calculated by the formula

.. math::

   \text{KE} = \frac{\text{dim}}{2} N k_B T,

where KE is the total kinetic energy of the group of atoms (sum of
:math:`\frac12 m v^2`, dim = 2 or 3 is the dimensionality of the
simulation, :math:`N` is the number of atoms in the group, :math:`k_B`
is the Boltzmann constant, and :math:`T` is the temperature.  Note that
:math:`v` in the kinetic energy formula is the atom's velocity with the
streaming component removed.

A symmetric tensor, stored as a six-element vector, is also calculated
by this compute for use in the computation of a pressure tensor by the
:doc:`compute pressue <compute_pressure>` command.  The formula for
the components of the tensor is also dictated by the internal temperature
compute. With :doc:`compute temp <compute_temp>` it is the same as the
above expression for :math:`E_\mathrm{kin}`, except that the 1/2 factor
is NOT included and the :math:`v_i^2` is replaced by :math:`v_{i,x} v_{i,y}`
for the :math:`xy` component, and so on.  Note that because it lacks
the 1/2 factor, these tensor components are twice those of the traditional
kinetic energy tensor.  The six components of the vector are ordered
:math:`xx`, :math:`yy`, :math:`zz`, :math:`xy`, :math:`xz`,
:math:`yz`.

The number of atoms contributing to the temperature is assumed to be
constant for the duration of the run; use the *dynamic/dof* option of the
:doc:`compute_modify <compute_modify>` command if this is not the case.
This will also flag the internal temperature compute to treat the number
of atoms as dynamic as if the following command had been issued:

.. code-block:: LAMMPS

   compute_modify internal-tcompute-ID dynamic/dof value

.. warning::

   Setting the dynamic/dof flag of the internal temperature compute
   but not compute temp/deform may lead to incorrect results.

The removal of the box deformation velocity component by this fix is
essentially computing the temperature after a "bias" has been removed
from the velocity of the atoms.  If this compute is used with a fix
command that performs thermostatting then this bias will be subtracted
from each atom, thermostatting of the remaining thermal velocity will
be performed, and the bias will be added back in.  Thermostatting
fixes that work in this way include :doc:`fix nvt <fix_nh>`,
:doc:`fix temp/rescale <fix_temp_rescale>`,
:doc:`fix temp/berendsen <fix_temp_berendsen>`, and
:doc:`fix langevin <fix_langevin>`.  If the internal
temperature compute also subtracts a bias, then it will be calculated
and subtracted after the box deformation component has been removed,
and the velocity after both biases have been subtracted is the one
to which the thermostat will be applied.

.. note::

   With compute temp as the internal temperature compute, or other
   temperature computes which don't calculate an additional bias from
   the atom velocities, the temperature calculated by this compute is
   only accurate if the atoms are indeed moving with a stream velocity
   profile that matches the box deformation.  If not, then the compute
   will subtract off an incorrect stream velocity, yielding a bogus thermal
   temperature.  You should **not** assume that your atoms are streaming at
   the same rate the box is deforming.  Rather, you should monitor their
   velocity profiles (e.g., via the :doc:`fix ave/chunk <fix_ave_chunk>`
   command).  You can also compare the results of this compute to
   :doc:`compute temp/profile <compute_temp_profile>`, which actually
   calculates the stream profile before subtracting it.  If the two computes do
   not give roughly the same temperature, then your atoms are not streaming
   consistent with the box deformation.  See the :doc:`fix deform <fix_deform>`
   command for more details on ways to get atoms to stream consistently with
   the box deformation.

Subtracting out degrees-of-freedom due to fixes that constrain molecular
motion, such as :doc:`fix shake <fix_shake>` and :doc:`fix rigid <fix_rigid>`
is handled by the internal temperature compute.  This means the temperature of
groups of atoms that include these constraints will be computed correctly.  If
needed, the subtracted degrees-of-freedom can be altered using the *extra/dof*
option of the :doc:`compute_modify <compute_modify>` command, which will
have the same effect as if the following command were issued:

.. code-block:: LAMMPS

   compute_modify internal-tcompute-ID extra/dof value

See the :doc:`Howto thermostat <Howto_thermostat>` page for a
discussion of different ways to compute temperature and perform
thermostatting.

----------

.. include:: accel_styles.rst

----------

Output info
"""""""""""

This compute calculates a global scalar (the temperature) and a global
vector of length 6 (symmetric tensor), which can be accessed by
indices 1--6.  These values can be used by any command that uses
global scalar or vector values from a compute as input.  See the
:doc:`Howto output <Howto_output>` page for an overview of LAMMPS
output options.

The scalar value calculated by this compute is "intensive".  The
vector values are "extensive".

The scalar value is in temperature :doc:`units <units>`.  The vector
values are in energy :doc:`units <units>`.

Restrictions
""""""""""""
none

Related commands
""""""""""""""""

:doc:`compute temp/ramp <compute_temp_ramp>`,
:doc:`compute temp/profile <compute_temp_profile>`,
:doc:`fix deform <fix_deform>`,
:doc:`fix nvt/sllod <fix_nvt_sllod>`

Default
"""""""

none
