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Electron poor materials research group. Group meeting Dec 2, 2010 Theory- Literature on Ionicity and electronegativity. Garcia and Cohen Phys. Rev. B 47, 4215 (1993). Charge assymetry coefficient defines a measure of charge transfer and electronegativity.
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Electron poor materials research group Group meeting Dec 2, 2010 Theory- Literature on Ionicity and electronegativity
Garcia and CohenPhys. Rev. B 47, 4215 (1993) • Charge assymetry coefficient defines a measure of charge transfer and electronegativity. • This tends to work on ANB8-N compounds. • Charge density ρ(r). • Symmetric charge density: • Assymmetric charge density:
Garcia and Cohencontinued… • SS & SA are a measure of the strength of the symmetry and assymmetry of the charge density over the whole unit cell of volume Ω. • Charge assymetry coefficient g is:
Colson, Redei & StockerProc. Roy. Soc. London 270, 357 (1962) • Ionicity is formed from probabilities of overlapping molecular orbitals. • This gives an atomic orbital of: • Fractions of the electrons on atoms A and B can then be described as: and .
Colson, Redei & Stockercontinued… • From this we can calculate the ionicity by: • And we are also able to calculate the charge on both atom A and B as: • λ is obtained by variation.
PaulingThe Nature of the Chemical Bond (Cornell University Press, Ithaca, 1960) • Based on the formational energy of bonds. • The electronegativity of atom A is XA and the energy of forming bond A-B is D(AB). C is a constant of dimension energy. • The ionicity for crystals is:
He, Wu, Wang, Liu & TangPRL 94, 015504 (2005) • Derived an ionicity scale to better map to their compound hardness model. • Pcand P are based on the Mulliken bond overlap population (J. Chem. Phys. 23, 1833 (1955)). • Pc is the bond overlap of a purely covalent crystal of the same structure as that of P.
