periodictable

The periodictable package provides an extensible periodic table containing various properties of the elements, such as name, symbol, mass, and density. It is specifically designed to provide data important to neutron and X-ray scattering experiments, allowing users to compute the scattering potential of a compound at a given wavelength using the elements package.

Because the table is extensible, third-party packages can add new properties to the existing structure without modifying the core package.

The periodictable package is an extensible periodic table that supports several scientific calculation domains:

• Mass and Density: Standard elemental properties.
• Neutron Scattering: Uses values from the neutron data booklet (Atomic Institute of the Austrian Universities), including energy-dependent scattering for rare earth elements (Lynn and Seeger, 1990).
• X-ray Scattering: Uses a combination of empirical and theoretical values from the LBL Center for X-ray Optics.
• Neutron Activation: Provides gross estimates of expected activation for a sample in a beam based on Shleien (1998), focusing on isotopes important to health physics. Note that this is a gross estimate and not a full activation analysis.

The periodictable package is in the public domain. However, users should check individual file headers, as specific files may contain separate copyright and licensing terms.

Disclaimer: The data provided by this package is compiled from various sources for convenience and does not constitute a critical evaluation. While efforts are made to verify values against published data, the values are based on measurements that may differ from specific experimental conditions.

If a requested property is not defined for a particular element, periodictable will return None instead of raising an error.

import periodictable
# Radon density might not be defined
print(periodictable.Rn.density)  # Returns None

For large datasets, instead of loading all data immediately upon import, use periodictable.core.delayed_load. This prevents slow import times by deferring data loading until the attribute is actually accessed.

delayed_load takes two arguments:

1. A list of attribute names that will be defined.
2. A loading function. The docstring of this function will be used as the attribute description.

When using delayed_load for isotope-specific data, you must set isotope=True in the call to ensure the magic delegation works correctly.

# discoverer/__init__.py
import periodictable
from periodictable.core import delayed_load

def load_discoverer(table):
    """Description of the discoverer attribute"""
    # Logic to populate discoverer
    pass

delayed_load(['discoverer'], load_discoverer)

To add properties that depend on the ion's state, use the ion=True keyword when calling delayed_load.

Note that ion-dependent properties can interact complexly with isotopes (e.g., Ni[58].ion[3]). While the library supports ion-specific data, some existing modules (like magnetic_ff) may require users to access properties via specific patterns like ion.magnetic_ff[ion.charge] rather than direct attribute access.

The periodic table is extensible via third-party packages. You can add attributes to all elements by defining a Python package that implements an init(table) function. This function attaches information to the periodic table so it is available on demand.

To add a simple attribute (like discoverer) to every element, create a module containing the init(table) function and call it with the default table instance.

# discoverer/discoverer.py
def init(table):
    for el in table:
        el.discoverer = "J. Black" # Example value

import periodictable
init(periodictable.core.default_table())

You can specify the density of a formula directly within the string using the @ tag. This is useful for isotopic density or natural density.

• Isotopic density: formula("D2O@1.112")
• Natural density: Use the n suffix, e.g., formula("D2O@1n"). This assumes isotope substitution does not change the unit cell volume.
• Mixtures: Density applies to the entire formula. For a mixture, specify the density of the resulting compound or the components.

Note: For volume-based mixtures, density must be known for individual components.

# Specify isotopic density
print(formula("D2O@1.112").density)

# Specify natural density
print(formula("D2O@1n").density)

# Mixture with density
print(formula("2D2O + H2O@1n").density)

After building the documentation, you can view the results at the following paths:

• HTML: periodictable/doc/sphinx/_build/html/index.html
• PDF: periodictable/doc/sphinx/_build/latex/PeriodicTable.pdf

Isotopes can be accessed using mass number subscripts on the element object (e.g., Ni[58]). Additionally, certain isotopes have special names, such as D for Deuterium and T for Tritium.

from periodictable import Ni, D, T

# Access specific isotope by mass number
print(Ni[58].neutron.coherent)

# Access special isotopes
print(D.mass)
print(T.mass)