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from __future__ import print_function
# Copyright (C) 2010, Jesper Friis
# (see accompanying license files for details).
"""
A module for ASE for simple creation of crystalline structures from
knowledge of the space group.
"""
import numpy as np
import ase
from ase.atoms import string2symbols
from ase.spacegroup import Spacegroup
from ase.geometry import cellpar_to_cell
__all__ = ['crystal']
def crystal(symbols=None, basis=None, spacegroup=1, setting=1,
cell=None, cellpar=None,
ab_normal=(0, 0, 1), a_direction=None, size=(1, 1, 1),
onduplicates='warn', symprec=0.001,
pbc=True, primitive_cell=False, **kwargs):
"""Create an Atoms instance for a conventional unit cell of a
space group.
Parameters:
symbols : str | sequence of str | sequence of Atom | Atoms
Element symbols of the unique sites. Can either be a string
formula or a sequence of element symbols. E.g. ('Na', 'Cl')
and 'NaCl' are equivalent. Can also be given as a sequence of
Atom objects or an Atoms object.
basis : list of scaled coordinates
Positions of the unique sites corresponding to symbols given
either as scaled positions or through an atoms instance. Not
needed if *symbols* is a sequence of Atom objects or an Atoms
object.
spacegroup : int | string | Spacegroup instance
Space group given either as its number in International Tables
or as its Hermann-Mauguin symbol.
setting : 1 | 2
Space group setting.
cell : 3x3 matrix
Unit cell vectors.
cellpar : [a, b, c, alpha, beta, gamma]
Cell parameters with angles in degree. Is not used when `cell`
is given.
ab_normal : vector
Is used to define the orientation of the unit cell relative
to the Cartesian system when `cell` is not given. It is the
normal vector of the plane spanned by a and b.
a_direction : vector
Defines the orientation of the unit cell a vector. a will be
parallel to the projection of `a_direction` onto the a-b plane.
size : 3 positive integers
How many times the conventional unit cell should be repeated
in each direction.
onduplicates : 'keep' | 'replace' | 'warn' | 'error'
Action if `basis` contain symmetry-equivalent positions:
'keep' - ignore additional symmetry-equivalent positions
'replace' - replace
'warn' - like 'keep', but issue an UserWarning
'error' - raises a SpacegroupValueError
symprec : float
Minimum "distance" betweed two sites in scaled coordinates
before they are counted as the same site.
pbc : one or three bools
Periodic boundary conditions flags. Examples: True,
False, 0, 1, (1, 1, 0), (True, False, False). Default
is True.
primitive_cell : bool
Wheter to return the primitive instead of the conventional
unit cell.
Keyword arguments:
All additional keyword arguments are passed on to the Atoms
constructor. Currently, probably the most useful additional
keyword arguments are `info`, `constraint` and `calculator`.
Examples:
Two diamond unit cells (space group number 227)
>>> diamond = crystal('C', [(0,0,0)], spacegroup=227,
... cellpar=[3.57, 3.57, 3.57, 90, 90, 90], size=(2,1,1))
>>> ase.view(diamond) # doctest: +SKIP
A CoSb3 skutterudite unit cell containing 32 atoms
>>> skutterudite = crystal(('Co', 'Sb'),
... basis=[(0.25,0.25,0.25), (0.0, 0.335, 0.158)],
... spacegroup=204, cellpar=[9.04, 9.04, 9.04, 90, 90, 90])
>>> len(skutterudite)
32
"""
sg = Spacegroup(spacegroup, setting)
if (not isinstance(symbols, str) and
hasattr(symbols, '__getitem__') and
len(symbols) > 0 and
isinstance(symbols[0], ase.Atom)):
symbols = ase.Atoms(symbols)
if isinstance(symbols, ase.Atoms):
basis = symbols
symbols = basis.get_chemical_symbols()
if isinstance(basis, ase.Atoms):
basis_coords = basis.get_scaled_positions()
if cell is None and cellpar is None:
cell = basis.cell
if symbols is None:
symbols = basis.get_chemical_symbols()
else:
basis_coords = np.array(basis, dtype=float, copy=False, ndmin=2)
sites, kinds = sg.equivalent_sites(basis_coords,
onduplicates=onduplicates,
symprec=symprec)
symbols = parse_symbols(symbols)
symbols = [symbols[i] for i in kinds]
if cell is None:
cell = cellpar_to_cell(cellpar, ab_normal, a_direction)
info = dict(spacegroup=sg)
if primitive_cell:
info['unit_cell'] = 'primitive'
else:
info['unit_cell'] = 'conventional'
if 'info' in kwargs:
info.update(kwargs['info'])
kwargs['info'] = info
atoms = ase.Atoms(symbols,
scaled_positions=sites,
cell=cell,
pbc=pbc,
**kwargs)
if isinstance(basis, ase.Atoms):
for name in basis.arrays:
if not atoms.has(name):
array = basis.get_array(name)
atoms.new_array(name, [array[i] for i in kinds],
dtype=array.dtype, shape=array.shape[1:])
if primitive_cell:
from ase.build import cut
prim_cell = sg.scaled_primitive_cell
atoms = cut(atoms, a=prim_cell[0], b=prim_cell[1], c=prim_cell[2])
if size != (1, 1, 1):
atoms = atoms.repeat(size)
return atoms
def parse_symbols(symbols):
"""Return `sumbols` as a sequence of element symbols."""
if isinstance(symbols, str):
symbols = string2symbols(symbols)
return symbols
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