(workflow)=

# Work flow

## Phonon calculations at constant volume

Work flow of phonopy is shown schematically. There are two ways to calculate,
(1) atomic forces from finite displacements and (2) given force constants. You
can choose one of them. Forces on atoms or force constants are calculated by
your favorite calculator (shown by the octagons in the work flow). The boxes are
jobs being done by phonopy, and the circles are input and intermediate output
data structures.

```{figure} procedure.png
:scale: 80
:align: center

Work flow of phonon calculation
```

## Combinations of phonon calculations at different volumes

Mode Grüneisen parameters can be calculated from two or three phonon calculation
results obtained at slightly different volume points. See the details at
{ref}`phonopy_gruneisen`.

With more volume points and fitting the thermal properties, thermal properties
at constant pressure are obtained under the (so-called) quasi-harmonic
approximation. See more details at {ref}`phonopy_qha`.
