# compute ke/eff command

## Syntax

```
compute ID group-ID ke/eff
```

- ID, group-ID are documented in
*compute*command - ke/eff = style name of this compute command

## Examples

```
compute 1 all ke/eff
```

## Description

Define a computation that calculates the kinetic energy of motion of a
group of eFF particles (nuclei and electrons), as modeled with the
*electronic force field*.

The kinetic energy for each nucleus is computed as 1/2 m v^2 and the kinetic energy for each electron is computed as 1/2(me v^2 + 3/4 me s^2), where m corresponds to the nuclear mass, me to the electron mass, v to the translational velocity of each particle, and s to the radial velocity of the electron, respectively.

There is a subtle difference between the quantity calculated by this
compute and the kinetic energy calculated by the *ke* or *etotal*
keyword used in thermodynamic output, as specified by the
*thermo_style* command. For this compute, kinetic
energy is “translational” and “radial” (only for electrons) kinetic
energy, calculated by the simple formula above. For thermodynamic
output, the *ke* keyword infers kinetic energy from the temperature of
the system with 1/2 Kb T of energy for each degree of freedom. For
the eFF temperature computation via the *compute temp_eff* command, these are the same. But
different computes that calculate temperature can subtract out
different non-thermal components of velocity and/or include other
degrees of freedom.

IMPRORTANT NOTE: The temperature in eFF models should be monitored via
the *compute temp/eff* command, which can be
printed with thermodynamic output by using the
*thermo_modify* command, as shown in the following
example:

```
compute effTemp all temp/eff
thermo_style custom step etotal pe ke temp press
thermo_modify temp effTemp
```

See *compute temp/eff*.

**Output info:**

This compute calculates a global scalar (the KE). This value can be used by any command that uses a global scalar value from a compute as input. See Section 6.15 for an overview of LAMMPS output options.

The scalar value calculated by this compute is “extensive”. The
scalar value will be in energy *units*.

## Restrictions

This compute is part of the USER-EFF package. It is only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

**Related commands:** none

**Default:** none