All-electron method
Definition:Quantum-mechanical methods which explicitly include all electrons of the participating atoms in the calculation of the electronic wave function (or density) in contrast to those which only include the outer (valence) electrons.
Explanation:The definition sounds trivial and refers to the most desirable case in the quantum theory of matter. In order to effectively deal with (very) large systems, however, a large number of theoretical methods nowadays sacrifice the detailed treatment of the core electrons. Indeed, the core electrons are not heavily engaged in the chemical bonding or chemical reactions, as indicated by the sheer existence of the periodic table. Hence, it is often sufficient and accurate enough to group the atomic nucleus and the inner electrons into one effective potential. In fact, there exist different ways to deal with these core potentials (→basis set), e.g. pseudo or PAW potentials. However, in some cases such as the calculation of NMR chemical shifts, it is advantageous to explicitly consider all the electrons; a popular example of the all-electron method is LAPW and the corresponding WIEN2k code [1]. Another example would be LMTO theory with the TB-LMTO-ASA code [2]. Here, additional speed is gained by using the orbitals which decays rapidly and enforces a local description of the electronic structure. In this way, the program performance can be prompt as well as reliable.
SFB-Link:The TB-LMTO-ASA code is used in several steel ab initio projects to calculate the electronic structures of chosen compounds and to allow for a transparent chemical interpretation.
References:[1] P. Blaha, K. Schwarz, G. Madsen, D. Kvasnicka, J. Luitz, WIEN2k, Technische Universität Wien 1999.
[2] G. Krier, O. Jepsen, A. Burkhardt, O. K. Andersen, The TB-LMTO-ASA program, version 4.7, Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.