Drude–Nernst equation (for electrostriction)

Equation describing the contraction ( $Δ V el$ ) taking place in a dielectric medium of relative static permittivity $ɛ r$ (formerly called dielectric constant) upon introduction of an ion of charge number $z$ and radius $r$ :

$Δ V el = − ( z e ) 2 2 r ɛ r ∂ ( ln ɛ r ) ∂ p$

with $e$ the elementary charge.

Note:

Inasmuch as the derivative of $ln ɛ r$ with respect to pressure, $∂ ( ln ɛ r ) ∂ p$ , is not known for all media, there are approximations to evaluate this term as a function of $ɛ r$ and of the isothermal compressibility of the medium, $κ T$ .

Source:

PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 327