from typing import Sequence
import numpy as np
from ase import Atoms
from clease.datastructures.system_changes import SystemChanges
from .mc_constraint import MCConstraint
[docs]class ConstrainSwapByBasis(MCConstraint):
"""
Constraint that restricts swaps of atoms within a given basis.
This constraint is intended to be used together with canonical
Monte Carlo calculations where the trial moves consist of swapping
two atoms.
Parameters:
atoms: Atoms object
ASE Atoms object used in the MC simulation
index_by_basis: List[List[int]]
Indices ordered by basis (same as ``index_by_basis`` parameter in
the :class:`~clease.settings.settings.ClusterExpansionSettings`
settings object.).
If an Atoms object has 10 sites where the first 4 belongs to the
first basis, the next 3 belongs to the next basis and the last 3
belongs to the last basis, the ``index_by_basis`` would be
[[0, 1, 2, 3], [4, 5, 6], [7, 8, 9]].
Note: swaps are only allowed within each basis, not across two basis.
"""
def __init__(self, atoms: Atoms, index_by_basis: Sequence[Sequence[int]]):
self.basis = np.zeros(len(atoms), dtype=int)
for i, indices in enumerate(index_by_basis):
for x in indices:
self.basis[x] = i
def __call__(self, system_changes: SystemChanges) -> bool:
if len(system_changes) != 2:
raise ValueError("ConstrainSwapByBasis requires swap move")
i1 = system_changes[0].index
b1 = self.basis[i1]
i2 = system_changes[1].index
b2 = self.basis[i2]
return b1 == b2