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### compute temp/ramp command

Syntax:

    compute ID group-ID temp/ramp vdim vlo vhi dim clo chi keyword value ...

- ID, group-ID are documented in compute command
- temp/ramp = style name of this compute command
- vdim = vx or vy or vz
- vlo,vhi = subtract velocities between vlo and vhi (velocity units)
- dim = x or y or z
- clo,chi = lower and upper bound of domain to subtract from (distance units)
- zero or more keyword/value pairs may be appended
- keyword = units

      units value = lattice or box

Examples:

    temperature 2nd middle ramp vx 0 8 y 2 12 units lattice

Description:

Define a computation that calculates the temperature of a group of atoms, after subtracting out an imposed velocity on the system before computing the kinetic energy. A compute of this style can be used by any command that computes a temperature, e.g. thermo_modify, fix temp/rescale, fix npt, etc.

The meaning of the arguments for this command is the same as for the velocity ramp command which was presumably used to impose the velocity.

The units keyword determines the meaning of the distance units used for coordinates (c1,c2) and velocities (vlo,vhi). A box value selects standard distance units as defined by the units command, e.g. Angstroms for units = real or metal. A lattice value means the distance units are in lattice spacings; e.g. velocity = lattice spacings / tau. The lattice command must have been previously used to define the lattice spacing.

A 6-component kinetic energy tensor is also calculated by this compute for use in the calculation of a pressure tensor. The formula for the components of the tensor is the same as the above formula, except that v^2 is replaced by vx * vy for the xy component, etc.

The number of atoms contributing to the temperature is assumed to be constant for the duration of the run; use the dynamic option of the compute_modify command if this is not the case.

The removal of the ramped 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.

This compute subtracts out degrees-of-freedom due to fixes that constrain molecular motion, such as fix shake and fix rigid. 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 option of the compute_modify command.

See this howto section of the manual for a discussion of different ways to compute temperature and perform thermostatting.

Output info:

The scalar value calculated by this compute is "intensive", meaning it is independent of the number of atoms in the simulation. The vector values are "extensive", meaning they scale with the number of atoms in the simulation.

Restrictions: none

Related commands:

compute temp, compute temp/region, compute temp/deform, compute pressure

Default:

The option default is units = lattice.