# 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 \(\frac{1}{2} m
v^2\) and the kinetic energy for each electron is computed as
\(\frac{1}{2}(m_e v^2 + \frac{3}{4} m_e s^2)\), where *m*
corresponds to the nuclear mass, \(m_e\) 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 \(\frac{1}{2} k_B T\) 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.

Warning

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 the Howto output doc page 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 Build package doc page for more info.

**Related commands:** none

**Default:** none