# fix nve/manifold/rattle command

## Syntax

    fix ID group-ID nve/manifold/rattle tol maxit manifold manifold-args keyword value ...

-   ID, group-ID are documented in [fix](fix) command

-   nve/manifold/rattle = style name of this fix command

-   tol = tolerance to which Newton iteration must converge

-   maxit = maximum number of iterations to perform

-   manifold = name of the manifold

-   manifold-args = parameters for the manifold

-   one or more keyword/value pairs may be appended

        keyword = *every*
          *every* values = N
            N = print info about iteration every N steps. N = 0 means no output

## Examples

``` LAMMPS
fix 1 all nve/manifold/rattle 1e-4 10 sphere 5.0
fix step all nve/manifold/rattle 1e-8 100 ellipsoid 2.5 2.5 5.0 every 25
```

## Description

Perform constant NVE integration to update position and velocity for
atoms constrained to a curved surface (manifold) in the group each
timestep. The constraint is handled by RATTLE [(Andersen)](Andersen1)
written out for the special case of single-particle constraints as
explained in [(Paquay)](Paquay2). V is volume; E is energy. This way,
the dynamics of particles constrained to curved surfaces can be studied.
If combined with [fix langevin](fix_langevin), this generates Brownian
motion of particles constrained to a curved surface. For a list of
currently supported manifolds and their parameters, see the [Howto
manifold](Howto_manifold) doc page.

Note that the particles must initially be close to the manifold in
question. If not, RATTLE will not be able to iterate until the
constraint is satisfied, and an error is generated. For simple manifolds
this can be achieved with *region* and *create_atoms* commands, but for
more complex surfaces it might be more useful to write a script.

The manifold args may be equal-style variables, like so:

``` LAMMPS
variable R equal "ramp(5.0,3.0)"
fix shrink_sphere all nve/manifold/rattle 1e-4 10 sphere v_R
```

In this case, the manifold parameter will change in time according to
the variable. This is not a problem for the time integrator as long as
the change of the manifold is slow with respect to the dynamics of the
particles. Note that if the manifold has to exert work on the particles
because of these changes, the total energy might not be conserved.

------------------------------------------------------------------------

## Restart, fix_modify, output, run start/stop, minimize info

No information about this fix is written to [binary restart
files](restart). None of the [fix_modify](fix_modify) options are
relevant to this fix. No global or per-atom quantities are stored by
this fix for access by various [output commands](Howto_output). No
parameter of this fix can be used with the *start/stop* keywords of the
[run](run) command. This fix is not invoked during [energy
minimization](minimize).

------------------------------------------------------------------------

## Restrictions

This fix is part of the MANIFOLD package. It is only enabled if LAMMPS
was built with that package. See the [Build package](Build_package) page
for more info.

------------------------------------------------------------------------

## Related commands

[fix nvt/manifold/rattle](fix_nvt_manifold_rattle), [fix
manifoldforce](fix_manifoldforce)

## Default

every = 0, tchain = 3

------------------------------------------------------------------------

::: {#Andersen1}
**(Andersen)** Andersen, J. Comp. Phys. 52, 24, (1983).
:::

::: {#Paquay2}
**(Paquay)** Paquay and Kusters, Biophys. J., 110, 6, (2016). preprint
available at [arXiv:1411.3019](https://arxiv.org/abs/1411.3019/)\_.
:::