smact.properties module

A collection of tools for estimating useful properties.

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 and the VBM/CBM 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. (1974). Phys. Rev. Lett., 33, 1088–1091. http://dx.doi.org/10.1103/PhysRevLett.33.1088
[2]Mulliken, R. S. (1934). J. Chem. Phys., 2, 782. http://dx.doi.org/10.1063/1.1749394
smact.properties.band_gap_Harrison(anion, cation, verbose=False, distance=None)[source]

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
  • verbose (bool) – An optional True/False flag. If True, additional
  • is printed to the standard output. [Defult (information) – False]
Returns :
Band_gap (float): Band gap in eV
smact.properties.compound_electroneg(verbose=False, elements=None, stoichs=None, source='Mulliken')[source]

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.
  • verbose (bool) – An optional True/False flag. If True, additional information is printed to the standard output. [Default: False]
  • 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)[source]

Get Mulliken electronegativity from the IE and EA.

Parameters:symbol (smact.Element or str) – Element object or symbol
Returns:Mulliken electronegativity
Return type:mulliken (float)