force_constant¶

Force constants are the 2nd derivatives of the energy with respect to displacement.

Force constants quantify the strength of interactions between atoms in a crystal lattice. They describe how the potential energy of the system changes with atomic displacements. Specifically they are the second derivative of the energy with respect to a displacement from their equilibrium positions. Force constants are a key component in determining the vibrational modes of a crystal lattice (phonon dispersion). Phonon calculations involve the computation of these force constants. Keep in mind that they are the second derivative at the equilibrium position so a careful relaxation is required to eliminate the first derivative (i.e. forces).

print()¶

Print a string representation of this instance.

read(*args, **kwargs)¶

Convenient wrapper around to_dict. Check that function for examples and optional arguments.

selections()¶

Returns possible alternatives for this particular quantity VASP can produce.

The returned dictionary contains a single item with the name of the quantity mapping to all possible selections. Each of these selection may be passed to other functions of this quantity to select which output of VASP is used.

Returns:

The key indicates this quantity and the values possible choices for arguments to other functions of this quantity.

Return type:

dict

to_dict()¶

Read structure information and force constants into a dictionary.

The structural information is added to inform about which atoms are included in the array. The force constants array contains the second derivatives with respect to atomic displacement for all atoms and directions.

Returns:

Contains structural information as well as the raw force constant data.

Return type:

dict