compute ke/atom/eff command — LAMMPS documentation

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# 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 \(\frac{1}{2} m v^2\), where m corresponds to the corresponding nuclear mass, 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 \(m_e\) 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 \(\frac{1}{2} k_B T\) 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 the Howto output page for an overview of LAMMPS output options.

The per-atom vector values will be in energy units.

## Restrictions

This compute is part of the EFF package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

## Related commands

dump custom

## Default

none