PLUGINS/FORCE AND STRESS

PLUGINS/FORCE_AND_STRESS = .True. | .False.
Default: PLUGINS/FORCE_AND_STRESS = .False.

Description: PLUGINS/FORCE_AND_STRESS calls the Python plugin for the force and stress interface for each ionic relaxation step

When PLUGINS/FORCE_AND_STRESS=.TRUE., VASP calls the force_and_stress Python function at the end of each ionic relaxation step. The primary use-case of this tag is to modify forces and the stress tensor to be consistent with modifications to the potential performed with PLUGINS/LOCAL_POTENTIAL

Expected inputs

The force_and_stress Python function expects the following inputs,

def force_and_stress(constants, additions):

where constants and additions and Python dataclasses. The constants dataclass consists of the following inputs, listed here with their associated datatypes

   ENCUT: float
   NELECT: float
   shape_grid: NDArray[np.int32]
   number_ions: int
   number_ion_types: int
   ion_types: NDArray[np.int32]
   atomic_numbers: NDArray[np.int32]
   lattice_vectors: NDArray[np.float64]
   positions: NDArray[np.float64]
   ZVAL: NDArray[np.float64]
   POMASS: NDArray[np.float64]
   forces: NDArray[np.float64]
   stress: NDArray[np.float64]
   charge_density: NDArray[np.float64]

Note that the INCAR tags are capitalized. shape_grid is a three dimensional integer array which stores the shape of the real space grid, NGXF, NGYF and NGZF, number_ions is the total number of ions listed in the POSCAR file, number_ion_types is the number of ion corresponding to each ion type in the convention of the POSCAR file, ion_types stores the total number of ion types, atomic_numbers contains the atomic number for each atom type, lattice_vectors and positions contain the lattice vectors and positions of the current SCF step forces and stress are the computed forces and stress tensor and charge_density contains the charge density on the real space grid. The additions dataclass consists of the following modifiable outputs

   total_energy: float
   forces: NDArray[np.float64]
   stress: NDArray[np.float64]

Modifying quantities

Modify the quantities listed in additions by adding to them. For example, if you wanted to add one to the forces

   def force_and_stress(constants, additions)
       additions.forces += np.ones((constants.number_ions,3))

Mind: You may not make modifications to quantities in constants