Polarizabilite

Polarizabilite, or polarizability in English, is a property of atoms, molecules, and ions that describes how easily their electron cloud can be distorted by an external electric field. When a static field E is applied, an induced electric dipole moment p is created. In the isotropic case, p = α E, where α is the static polarizability. For anisotropic systems, the response is tensorial: p_i = sum_j α_ij E_j, with principal components α_xx, α_yy, α_zz.

Units and conventions: in SI units, α has dimensions of C·m^2/V (often written as C·m^2·V^-1). Chemists and physicists frequently use volumetric units such as cubic ångströms (Å^3) or atomic units (a.u.). The value of polarizability grows with the size and the number of electrons, and it varies with the electronic state of the species.

Dynamic polarizability: α(ω) describes the response to oscillating electric fields (light) and is generally complex, reflecting absorption and dispersion. The static polarizability is the ω → 0 limit of α(ω). Polarizability is linked to optical properties such as refractive index and dielectric constant and plays a key role in dispersion forces between molecules (London forces).

Measurement and calculation: polarizability can be inferred from experimental data such as refractive index dispersion, Rayleigh scattering, or Stark spectroscopy, and is routinely calculated by quantum chemical methods, including Hartree–Fock, density functional theory, and post-Hartree–Fock approaches. The tensor components provide a complete description for non-spherical species.

Significance: polarizability influences intermolecular interactions, dielectric behavior, nonlinear optics, and the response of matter to electric fields in both fundamental and applied contexts.