Wave-function-based ab initio method for metals : Application of the incremental scheme to magnesium

TL;DR: In this article, the Hartree-Fock (HF) self-consistent field result for the infinite system was used to calculate correlation effects on cohesive properties of Mg, thereby extending the method of increments to metallic systems.

Abstract: We apply ab initio quantum-chemical methods to calculate correlation effects on cohesive properties of Mg, thereby extending the method of increments to metallic systems. Metals require special treatment because of two distinct features. Since the conduction bands are only partially filled, we cannot construct well localized orbitals from them. Furthermore, we must deal properly with charge screening which obviously is a correlation effect. A starting point for treatment of the many-body correlation effects in solids is a reliable Hartree-Fock (HF) self-consistent-field result for the infinite system. In the case of Mg, the HF cohesive energy of the solid is significantly underestimated with respect to the experimental value. Summing up all correlation contributions, we obtain nearly 100% of the difference between the experimental and HF cohesive energies. Ignoring the correlations, HF model gives rather good agreement with experiment of one lattice parameter $(c)$, but incorrect value for $c∕a$ ratio because of the too large lattice constant $a$. Application of the method of increments allows us not only to improve the HF values, giving deviation by about 1% from experimental values, but also to explain the reason for these changes.