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# compute temp/deform command

Accelerator Variants: temp/deform/kk

## Syntax

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

- ID, group-ID are documented in compute command

- temp/deform = style name of this compute command

- zero or more keyword/value pairs may be appended

- keyword = temp

      temp value = compute ID that calculates a temperature

## Examples

    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 fix deform command. A compute of this style is created by the 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., thermo_modify, fix temp/rescale, fix npt).

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.

Changed in version 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, compute temp is used, and the internal temperature compute is created automatically as if the following command had been issued:

    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 compute temp/partial, or account for additional bias beyond that due to deformation by using 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 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

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 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 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 compute temp as the internal temperature compute (the default), the temperature is calculated by the formula

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

where KE is the total kinetic energy of the group of atoms (sum of \(\frac12 m v^2\), dim = 2 or 3 is the dimensionality of the simulation, \(N\) is the number of atoms in the group, \(k_B\) is the Boltzmann constant, and \(T\) is the temperature. Note that \(v\) 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 compute pressue command. The formula for the components of the tensor is also dictated by the internal temperature compute. With compute temp it is the same as the above expression for \(E_\mathrm{kin}\), except that the 1/2 factor is NOT included and the \(v_i^2\) is replaced by \(v_{i,x} v_{i,y}\) for the \(xy\) 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 \(xx\), \(yy\), \(zz\), \(xy\), \(xz\), \(yz\).

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 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:

    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 fix nvt, fix temp/rescale, fix temp/berendsen, and 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 fix ave/chunk command). You can also compare the results of this compute to 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 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 fix shake and 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 compute_modify command, which will have the same effect as if the following command were issued:

    compute_modify internal-tcompute-ID extra/dof value

See the Howto thermostat page for a discussion of different ways to compute temperature and perform thermostatting.

Styles with a gpu, intel, kk, omp, or opt suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed on the Accelerator packages page. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.

These accelerated styles are part of the GPU, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package page for more info.

You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.

See the Accelerator packages page for more instructions on how to use the accelerated styles effectively.

## 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 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 units. The vector values are in energy units.

## Restrictions

none

## Related commands

compute temp/ramp, compute temp/profile, fix deform, fix nvt/sllod

## Default

none