On the origin of bonding in metals: lithium as a case study

The bonding in metals is analysed within the framework of the PATMOS (Perturbed AToms in MOlecules and Solids) model. The electronic binding energy per atom is written as a sum of a distortion energy of the atoms and the partitioned interaction energy comprising Coulombic, exchange and correlation terms. The adopted physical model of the infinite system, is spherical embedding of the atoms of the reference unit cell. Correlation energies are calculated by second-order Moller-Plesset and second-order Epstein-Nesbet perturbation theory. The binding energy of lithium solid is calculated for 16 nearest neighbour distances from 4.0 to 10.0 Bohr. Electron correlation is of paramount importance for the binding energy. The calculated cohesive energy is (0.0571\pm 0.004) (0.0571 +/- 0.004) Hartree comparing with experimental value 0.0599 Hartree. The bonding picture is characterised by slightly expanded atomic orbitals. [GRAPHICS] .