# 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.

## 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 Calculation of mode Grüneisen parameters.

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 Quasi harmonic approximation.