Debye

Debye refers to several related concepts in physics and chemistry, named after the Dutch-American physicist and physical chemist Peter Joseph Wilhelm Debye (1884–1966). Debye was awarded the Nobel Prize in Chemistry in 1936 for his work on the structure of molecules and dipole moments, and he made foundational contributions to the understanding of dielectric properties, molecular dipoles, and ionic solutions. His work helped establish theoretical frameworks that bear his name, including the Debye model of solids and the Debye–Hückel theory of electrolytes.

The Debye unit, or the Debye (symbol D), is a CGS unit of electric dipole moment. It is defined as 3.33564 × 10^-30 coulomb-meters and is commonly used in molecular physics and chemistry to express the strength of molecular dipoles.

The Debye model is a theory of lattice vibrations in solids developed by Debye in 1912. It provides a more accurate description of the specific heat at low temperatures than earlier models by treating vibrational modes as a continuum up to a maximum frequency, the Debye frequency. This leads to characteristic predictions such as the low-temperature heat capacity varying as T^3 and introduces the Debye temperature ΘD.

The Debye length is a screening length in plasmas and electrolyte solutions that characterizes how electric fields are attenuated by mobile charge carriers. In SI units, it is given by λD ≈ sqrt(ε0 kB T / (n e^2)), where temperature, charge density, and other constants set the scale of electrostatic screening.

The Debye–Hückel theory describes how ionic atmospheres around charged species in dilute solutions modify activity coefficients, accounting for electrostatic interactions among ions. It is a foundational concept in physical chemistry, though its applicability narrows at higher ionic strengths.