Frenkel

Frenkel is a surname of Slavic origin. In science, it is associated with several concepts named after the Soviet physicist Yakov Frenkel, including the Frenkel exciton, the Frenkel defect in crystals, and the Frenkel–Kontorova model.

Frenkel exciton: In molecular crystals and organic solids, a Frenkel exciton is an excited electronic state in which the electron-hole pair is localized on a single molecule or lattice site rather than spread over many sites. The excitation can migrate by hopping between neighboring sites, and the exciton is typically tightly bound with a radius comparable to or smaller than the lattice spacing. This contrasts with Wannier–Mott excitons found in many inorganic semiconductors, which are more delocalized.

Frenkel defect: In ionic crystals, a Frenkel defect consists of a vacancy created when an ion leaves its lattice site and occupies a neighboring interstitial site, forming a vacancy–interstitial pair. It occurs more readily when there is a size disparity between ions. Classic examples include silver chloride (AgCl). The Frenkel defect is distinct from the Schottky defect, which involves vacancies of multiple ions without corresponding interstitials.

Frenkel–Kontorova model: A theoretical model developed by Yakov Frenkel and S. Kontorova to study friction, dislocations, and commensurate–incommensurate transitions. It describes a chain of particles connected by springs moving in a periodic potential and is used to explore nonlinear dynamics and solitons.

The term Frenkel is also a surname borne by various individuals; many uses in science trace back to Yakov Frenkel.