# compute ke/atom/eff command

## Syntax

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

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

## Examples

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

## Description

Define a computation that calculates the per-atom translational
(nuclei and electrons) and radial kinetic energy (electron only) in a
group. The particles are assumed to be nuclei and electrons modeled
with the *electronic force field*.

The kinetic energy for each nucleus is computed as 1/2 m v^2, where m corresponds to the corresponding nuclear mass, and the kinetic energy for each electron is computed as 1/2 (me v^2 + 3/4 me s^2), where me and v correspond to the mass and translational velocity of each electron, and s to its radial velocity, 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” plus electronic “radial” 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 (nuclear-only) degree of freedom in
eFF.

Note

The temperature in eFF 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
```

The value of the kinetic energy will be 0.0 for atoms (nuclei or electrons) not in the specified compute group.

**Output info:**

This compute calculates a scalar quantity for each atom, which can be accessed by any command that uses per-atom computes as input. See Section 6.15 for an overview of LAMMPS output options.

The per-atom vector values 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.