allelectron

All-electron, sometimes written allelectron, denotes an approach to electronic-structure calculations in quantum chemistry and solid-state physics that treats every electron in a system explicitly. Unlike pseudopotential or effective core potential methods, which replace core electrons with an abstract potential, all-electron methods aim to describe the full electron density and interactions, including regions close to atomic nuclei.

In molecular calculations, all-electron approaches use basis sets or numerical orbitals that describe core and valence electrons on equal footing. Common choices include Gaussian basis sets (for example, correlation-consistent cc-pVXZ sets) and numerical atomic orbitals. They are favored when core properties or high-precision electron densities are required, or when core-level spectroscopies are studied.

In solid-state physics, all-electron methods such as full-potential linearized augmented plane wave (FP-LAPW) treat the full electron density without approximating the core region. Well-known implementations include WIEN2k, ELK, and FHI-aims, which can incorporate relativistic effects and spin-orbit coupling.

Relativistic treatment in all-electron calculations can be scalar-relativistic or fully four-component Dirac form, with spin-orbit coupling often included self-consistently for heavy elements. All-electron methods are computationally demanding and scale less favorably with system size than pseudopotential methods, limiting their use to smaller molecules or periodic systems unless specialized algorithms are employed.

Applications include high-accuracy benchmarks, core-level spectroscopy simulations, and properties sensitive to electron density near nuclei. Researchers choose all-electron methods when accuracy at the nucleus is essential or when pseudopotentials would introduce unacceptable approximations.