smact.properties module

A collection of tools for estimating physical properties based on chemical composition.

The “electronegativity of a compound” computed with compound_electroneg() is the rescaled geometric mean of electronegativity used in Nethercot’s recipe for estimating the photoelectric threshold: [1]

\[\Phi^{AB} = 2.86(\chi_{A}\chi_{B})^{1/2} + E_{g} / 2.\]

In other words, the computed group \(2.86(\chi_{A}\chi_{B})^{1/2}\) is the mid-gap energy. The valence band maximum/conduction band minimum positions can be estimated by subtracting/adding half of the band gap \(E_g\). This is an extension Mulliken’s electronegativity scale in which \(\chi_{A} = (I_{A} + E_{A})/2\) (where \(I\) and \(E\) are respectively the ionisation potential and electron affinity.) [2]

[1]

Nethercot, A. H., Prediction of Fermi energies and photoelectric thresholds based on electronegativity concepts Phys. Rev. Lett. 33, 1088–1091 (1974). http://dx.doi.org/10.1103/PhysRevLett.33.1088

[2]

Mulliken, R. S., A new electroaffinity scale; together with data on valence states and on valence ionization potentials and electron affinities J. Chem. Phys. 2, 782 (1934). http://dx.doi.org/10.1063/1.1749394

A collection of tools for estimating physical properties based on chemical composition.

smact.properties.band_gap_Harrison(anion: str, cation: str, distance: float | str = 2.0) → float

Estimates the band gap from elemental data.

The band gap is estimated using the principles outlined in Harrison’s 1980 work “Electronic Structure and the Properties of Solids: The Physics of the Chemical Bond”.

Parameters:

• anion (str) – Element symbol of the dominant anion in the system

• cation (str) – Element symbol of the the dominant cation in the system

• distance (float or str) – Nuclear separation between anion and cation, i.e. sum of ionic radii (in Angstroms). Default: 2.0.

Returns:

Band gap in eV

Return type:

Band_gap (float)

smact.properties.compound_electroneg(elements: list[str | Element] | None = None, stoichs: list[int | float] | None = None, source: str = 'Mulliken') → float

Estimate electronegativity of compound from elemental data.

Uses Mulliken electronegativity by default, which uses elemental ionisation potentials and electron affinities. Alternatively, can use Pauling electronegativity, re-scaled by factor 2.86 to achieve same scale as Mulliken method (Nethercot, 1974) DOI:10.1103/PhysRevLett.33.1088 .

Geometric mean is used (n-th root of product of components), e.g.:

X_Cu2S = (X_Cu * X_Cu * C_S)^(1/3)

Parameters:

• elements (list) – Elements given as standard elemental symbols.

• stoichs (list) – Stoichiometries, given as integers or floats.

• source – String ‘Mulliken’ or ‘Pauling’; type of Electronegativity to use. Note that in SMACT, Pauling electronegativities are rescaled to a Mulliken-like scale.

Returns:

Estimated electronegativity (no units).

Return type:

Electronegativity (float)

smact.properties.eneg_mulliken(element: Element | str) → float

Get Mulliken electronegativity from the IE and EA.

Parameters:

element (smact.Element or str) – Element object or symbol

Returns:

Mulliken electronegativity

Return type:

mulliken (float)

smact.properties.valence_electron_count(compound: str) → float

Calculate the Valence Electron Count (VEC) for a given chemical compound.

This function parses the input compound, extracts the elements and their stoichiometries, and calculates the VEC using the valence electron data from SMACT’s Element class.

Parameters:

compound (str) – Chemical formula of the compound (e.g., “Fe2O3”).

Returns:

Valence Electron Count (VEC) for the compound.

Return type:

float

Raises:

ValueError – If an element in the compound is not found in the valence data.