compute dpd command — LAMMPS documentation

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# compute dpd command

## Syntax

    compute ID group-ID dpd

- ID, group-ID are documented in compute command

- dpd = style name of this compute command

## Examples

    compute 1 all dpd

## Description

Define a computation that accumulates the total internal conductive energy (\(U^{\text{cond}}\)), the total internal mechanical energy (\(U^{\text{mech}}\)), the total chemical energy (\(U^\text{chem}\)) and the harmonic average of the internal temperature (\(\theta_\text{avg}\)) for the entire system of particles. See the compute dpd/atom command if you want per-particle internal energies and internal temperatures.

The system internal properties are computed according to the following relations:

\[\begin{split}U^\text{cond} = & \sum_{i=1}^{N} u_{i}^\text{cond} \\ U^\text{mech} = & \sum_{i=1}^{N} u_{i}^\text{mech} \\ U^\text{chem} = & \sum_{i=1}^{N} u_{i}^\text{chem} \\ U = & \sum_{i=1}^{N} (u_{i}^\text{cond} + u_{i}^\text{mech} + u_{i}^\text{chem}) \\ \theta_{avg} = & \biggl(\frac{1}{N}\sum_{i=1}^{N} \frac{1}{\theta_{i}}\biggr)^{-1} \\\end{split}\]

where \(N\) is the number of particles in the system.

## Output info

This compute calculates a global vector of length 5 (\(U^\text{cond}\), \(U^\text{mech}\), \(U^\text{chem}\), \(\theta_\text{avg}\), \(N\)), which can be accessed by indices 1 through 5. See the Howto output page for an overview of LAMMPS output options.

The vector values will be in energy and temperature units.

## Restrictions

This command is part of the DPD-REACT package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

This command also requires use of the atom_style dpd command.

## Related commands

compute dpd/atom, thermo_style

## Default

none

(Larentzos) J.P. Larentzos, J.K. Brennan, J.D. Moore, and W.D. Mattson, “LAMMPS Implementation of Constant Energy Dissipative Particle Dynamics (DPD-E)”, ARL-TR-6863, U.S. Army Research Laboratory, Aberdeen Proving Ground, MD (2014).