# angle_style spica command

Accelerator Variants: *spica/omp*

## Syntax

``` LAMMPS
angle_style spica

angle_style spica/omp
```

## Examples

``` LAMMPS
angle_style spica
angle_coeff 1 300.0 107.0
```

## Description

The *spica* angle style is a combination of the harmonic angle
potential,

$$E = K (\theta - \theta_0)^2$$

where $\theta_0$ is the equilibrium value of the angle and $K$ a
prefactor, with the *repulsive* part of the non-bonded *lj/spica* pair
style between the atoms 1 and 3. This angle potential is intended for
coarse grained MD simulations with the SPICA (formerly called SDK)
parameterization using the [pair_style lj/spica](pair_spica). Relative
to the pair_style *lj/spica*, however, the energy is shifted by
$\epsilon$, to avoid sudden jumps. Note that the usual 1/2 factor is
included in $K$.

The following coefficients must be defined for each angle type via the
[angle_coeff](angle_coeff) command as in the example above:

-   $K$ (energy)
-   $\theta_0$ (degrees)

$\theta_0$ is specified in degrees, but LAMMPS converts it to radians
internally; hence $K$ is effectively energy per radian\^2.

The required *lj/spica* parameters are extracted automatically from the
pair_style.

Style *sdk*, the original implementation of style *spica*, is available
for backward compatibility.

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

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](Speed_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](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](Run_options) when you invoke LAMMPS, or you can use the
[suffix](suffix) command in your input script.

See the [Accelerator packages](Speed_packages) page for more
instructions on how to use the accelerated styles effectively.

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

## Restrictions

This angle style can only be used if LAMMPS was built with the CG-SPICA
package. See the [Build package](Build_package) doc page for more info.

## Related commands

[angle_coeff](angle_coeff), [angle_style harmonic](angle_harmonic),
[pair_style lj/spica](pair_spica), [pair_style
lj/spica/coul/long](pair_spica)

## Default

none