This section gives a brief introduction about some of the tools available in pyiron to construct atomic structures.
For the sake of compatibility, our structure class is written to be compatible with the popular Atomistic Simulation Environment package (ASE). This makes it possible to use routines from ASE to help set-up structures.
Furthermore, pyiron uses the NGLview package to visualize the structures and trajectories interactively in 3D using NGLview-widgets.
As preparation for the following discussion we import a few python libraries
import numpy as np
%matplotlib inline
import matplotlib.pylab as plt
and create a pyiron project named 'structures':
from pyiron.project import Project
pr = Project(path='structures')
In this section we discuss various possibilities to create bulk crystal structures.
create_structure()
¶The simplest way to generate simple crystal structures is using the inbuilt create_structure()
function specifying the element symbol, Bravais basis and the lattice constant(s)
Note: The output gives a cubic cell rather than the smallest non-orthogonal unit cell.
structure = pr.create_structure('Al',
bravais_basis='fcc',
lattice_constant=4.05)
To plot the structure interactively in 3D simply use:
structure.plot3d()
_ColormakerRegistry()
NGLWidget()
create_ase_bulk()
¶Another convenient way to set up structures is using the create_ase_bulk()
function which is built on top of the ASE build package for bulk crystals. This function returns an object which is of the pyiron structure object type.
Example: fcc bulk aluminum in a cubic cell
structure = pr.create_ase_bulk('Al', cubic=True)
structure.plot3d()
NGLWidget()
Example: wurtzite GaN in a 3x3x3 repeated orthorhombic cell.
Note:
spacefill=False
in the plot3d()
method changes the atomic structure style to "ball and stick".structure = pr.create_ase_bulk('AlN',
crystalstructure='wurtzite',
a=3.5, orthorhombic=True)
structure.set_repeat([3,3,3])
structure.plot3d(spacefill=False)
NGLWidget()
Example: Creating a 3x4 fcc Al(111) surface with 4 layers and a vacuum of 10 Ångström
Al_111 = pr.create_surface("Al", surface_type="fcc111",
size=(3, 4, 4), vacuum=10, orthogonal=True)
Al_111.plot3d()
NGLWidget()
In all the examples shown above, the structures are create from the pyiron Project
object. It is also possible to do this without importing/initializing this object. For this the appropriate imports must be made.
from pyiron import create_ase_bulk, create_surface
structure = create_ase_bulk('AlN',
crystalstructure='wurtzite',
a=3.5, orthorhombic=True)
structure.set_repeat([3,3,3])
structure.plot3d(spacefill=False)
NGLWidget()
Al_111 = create_surface("Al", surface_type="fcc111",
size=(3, 4, 4), vacuum=10, orthogonal=True)
Al_111.plot3d()
NGLWidget()
from ase.spacegroup import crystal
from pyiron import ase_to_pyiron
a = 9.04
skutterudite = crystal(('Co', 'Sb'),
basis=[(0.25, 0.25, 0.25), (0.0, 0.335, 0.158)],
spacegroup=204,
cellpar=[a, a, a, 90, 90, 90])
skutterudite = ase_to_pyiron(skutterudite)
skutterudite.plot3d()
NGLWidget()
Using the bulk aluminum fcc example from before the structure object can be created by
structure = pr.create_ase_bulk('Al', cubic=True)
A summary of the information about the structure is given by using
print(structure)
Al: [0. 0. 0.] Al: [0. 2.025 2.025] Al: [2.025 0. 2.025] Al: [2.025 2.025 0. ] pbc: [ True True True] cell: [[4.05 0. 0. ] [0. 4.05 0. ] [0. 0. 4.05]]
The cell vectors of the structure object can be accessed and edited through
structure.cell
array([[4.05, 0. , 0. ], [0. , 4.05, 0. ], [0. , 0. , 4.05]])
The positions of the atoms in the structure object can be accessed and edited through
structure.positions
array([[0. , 0. , 0. ], [0. , 2.025, 2.025], [2.025, 0. , 2.025], [2.025, 2.025, 0. ]])
We start by setting up a 4x4x4 supercell
structure = pr.create_ase_bulk('Al', cubic=True)
structure.set_repeat([4,4,4])
To create the vacancy at position index "0" simply use:
del structure[0]
To plot the structure that now contains a vacancy run:
structure.plot3d()
NGLWidget()
# First create a 4x4x4 supercell
structure = pr.create_ase_bulk('Al', cubic=True)
structure.set_repeat([4,4,4])
print('Number of atoms in the repeat unit: ',structure.get_number_of_atoms())
Number of atoms in the repeat unit: 256
The del
command works for passing a list of indices to the structure object. For example, a random set of n$_{\text{vac}}$ vacancies can be created by using
# Generate a list of indices for the vacancies
n_vac = 24
vac_ind_lst = np.random.permutation(len(structure))[:n_vac]
# Remove atoms according to the "vac_ind_lst"
del structure[vac_ind_lst]
# Visualize the structure
print('Number of atoms in the repeat unit: ',structure.get_number_of_atoms())
structure.plot3d()
Number of atoms in the repeat unit: 232
NGLWidget()
# Create a 4x4x4 supercell
structure = pr.create_ase_bulk('Al', cubic=True)
structure.set_repeat([4,4,4])
Substitutional atoms can be defined by changing the atomic species accessed through its position index.
Here, we set $n_{\text{sub}}$ magnesium substitutional atoms at random positions
n_sub = 24
structure[np.random.permutation(len(structure))[:n_sub]] = 'Mg'
# Visualize the structure and print some additional information about the structure
print('Number of atoms in the repeat unit: ',structure.get_number_of_atoms())
print('Chemical formula: ',structure.get_chemical_formula())
structure.plot3d()
Number of atoms in the repeat unit: 256 Chemical formula: Al232Mg24
NGLWidget()
You can also set-up structures through the explicit input of the cell parameters and positions
cell = 10.0 * np.eye(3) # Specifying the cell dimensions
positions = [[0.25, 0.25, 0.25], [0.75, 0.75, 0.75]]
elements = ['O', 'O']
# Now use the Atoms class to create the instance.
O_dimer = pr.create_atoms(elements=elements, scaled_positions=positions, cell=cell)
O_dimer.plot3d()
NGLWidget()
Parsers from ASE can be used to import structures from other formats. In this example, we will download and import a Nepheline structure from the Crystallography Open Database (COD)
# The COD structures can be accessed through their unique COD identifier
cod = 1008753
filename = '{}.cif'.format(cod)
url = 'http://www.crystallography.net/cod/{}'.format(filename)
# Download and save the structure file locally
import urllib
urllib.request.urlretrieve(url=url, filename='strucs.'+filename);
# Using ase parsers to read the structure and then convert to a pyiron instance
import ase
from pyiron import ase_to_pyiron
structure = ase_to_pyiron(ase.io.read(filename='strucs.'+filename,
format='cif'))
structure.info["cod"] = cod
/home/surendralal/miniconda3/envs/pyiron_workshop/lib/python3.7/site-packages/ase/io/cif.py:375: UserWarning: crystal system 'hexagonal' is not interpreted for space group Spacegroup(173, setting=1). This may result in wrong setting! setting_name, spacegroup))
structure.plot3d()
--------------------------------------------------------------------------- ModuleNotFoundError Traceback (most recent call last) ~/science/phd/dev/pyiron/pyiron/atomistics/structure/atoms.py in plot3d(self, show_cell, show_axes, camera, spacefill, particle_size, select_atoms, background, color_scheme, colors, scalar_field, scalar_start, scalar_end, scalar_cmap, vector_field, vector_color, magnetic_moments, custom_array, custom_3darray, view_plane, distance_from_camera) 1326 try: # If the graphical packages are not available, the GUI will not work. -> 1327 import nglview 1328 except ImportError: ModuleNotFoundError: No module named 'nglview' During handling of the above exception, another exception occurred: ImportError Traceback (most recent call last) <ipython-input-30-184096eccb97> in <module> ----> 1 structure.plot3d() ~/science/phd/dev/pyiron/pyiron/atomistics/structure/atoms.py in plot3d(self, show_cell, show_axes, camera, spacefill, particle_size, select_atoms, background, color_scheme, colors, scalar_field, scalar_start, scalar_end, scalar_cmap, vector_field, vector_color, magnetic_moments, custom_array, custom_3darray, view_plane, distance_from_camera) 1327 import nglview 1328 except ImportError: -> 1329 raise ImportError( 1330 "The package nglview needs to be installed for the plot3d() function!" 1331 ) ImportError: The package nglview needs to be installed for the plot3d() function!
Structures can be stored indepently from jobs in HDF5 by using the special StructureContainer
job. To save to disk, call run()
.
container = pr.create_job(pr.job_type.StructureContainer, "nepheline")
container.structure = structure
container.run()
The job nepheline was saved and received the ID: 47
It's also possible to store multiple structures in one container and to store directly from a job. Let's use this here to store the equilibrated structures at finite temperatures.
al_container = pr.create_job(pr.job_type.StructureContainer, "al_temp", delete_existing_job=True)
for T in (400, 600, 800):
j = pr.create_job(pr.job_type.Lammps, "T_{}".format(T))
j.structure = pr.create_ase_bulk("Al", cubic = True)
j.potential = j.list_potentials()[0]
j.calc_md(temperature=T, n_ionic_steps=1000, pressure=0)
j.run()
structure = j.get_structure(-1)
structure.info["T"] = T
structure.info["P"] = 0
al_container.append(structure)
al_container.run()
This group does not exist in the HDF5 file al_temp
2020-08-22 14:05:03,496 - pyiron_log - WARNING - The job T_400 is being loaded instead of running. To re-run use the argument 'delete_existing_job=True in create_job' 2020-08-22 14:05:04,282 - pyiron_log - WARNING - The job T_600 is being loaded instead of running. To re-run use the argument 'delete_existing_job=True in create_job' 2020-08-22 14:05:05,065 - pyiron_log - WARNING - The job T_800 is being loaded instead of running. To re-run use the argument 'delete_existing_job=True in create_job'
The job al_temp was saved and received the ID: 51
al_container.structure_lst[0].info
{'T': 400, 'P': 0}
al_container.structure_lst
InputList([Al: [0.13389146 3.96541338 4.05893092] Al: [3.99018226 2.0071096 1.95618182] Al: [1.98560236 3.88778884 2.0465924 ] Al: [2.04906472 2.05913422 0.09311447] pbc: [ True True True] cell: Cell([[4.079370396328773, 2.497893949200251e-16, 2.497893949200251e-16], [0.0, 3.973148678151775, 2.4328519056175543e-16], [0.0, 0.0, 4.077409804014061]]) , Al: [0.0070279 4.03832899 0.08383998] Al: [4.08339864 2.06533333 2.03444326] Al: [2.20534808 4.07618808 1.94632881] Al: [1.91118709 2.15964157 0.05514228] pbc: [ True True True] cell: Cell([[4.103480856873615, 2.5126573483663555e-16, 2.5126573483663555e-16], [0.0, 4.113163987813141, 2.518586556021763e-16], [0.0, 0.0, 4.11975432838738]]) , Al: [3.7382874 0.12171228 4.27645154] Al: [0.05199557 1.91099383 2.20493355] Al: [1.92074788 0.03592662 2.13915097] Al: [1.89264518 1.93451826 0.04368514] pbc: [ True True True] cell: Cell([[3.801838019513017, 2.3279543807366644e-16, 2.3279543807366644e-16], [0.0, 4.003150985990484, 2.4512230207484086e-16], [0.0, 0.0, 4.332110602330073]]) ])