\(\renewcommand{\AA}{\text{Å}}\)

compute ke command

Accelerator Variants: ke/kk

Syntax

compute ID group-ID ke

  • ID, group-ID are documented in compute command

  • ke = style name of this compute command

Examples

compute 1 all ke

Description

Define a computation that calculates the translational kinetic energy of a group of particles.

The kinetic energy of each particle is computed as \(\frac{1}{2} m v^2\), where m and v are the mass and velocity of the particle, 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” 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 default temperature computation via the compute temp command, these are the same. However, different computes that calculate temperature can subtract out different non-thermal components of velocity and/or include different degrees of freedom (translational, rotational, etc.).

Output info

This compute calculates a global scalar (the summed 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.

Styles with a gpu, intel, kk, omp, or opt suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed on the Accelerator packages page. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.

These accelerated styles are part of the GPU, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package page for more info.

You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.

See the Accelerator packages page for more instructions on how to use the accelerated styles effectively.

Restrictions

none

Default

none