A FIRST-PRINCIPLES STUDY OF THE LATTICE DISTORTION AROUND A SOLUTE-ATOM IN BCC LITHIUM

In this paper, we study the effect that the lattice distortion around a solute atom (Na, Mg, Al) has on the electronic and mechanical proper ties of BCC Li using the first-principles structural optimization meth od. In the present calculations, a 54-site supercell is used to get a better insight into the long-range behaviour of the lattice distortion around a solute atom. The results show that the behaviour of the firs t-nearest-neighbouring Li shell around a solute atom in all cases inve stigated is similar to that obtained in the corresponding 16-site supe rcell calculations. The distortion has, for instance, an effect on the average atomic volume, bulk modulus and heat of formation of Li alloy s. From the present calculations, together with our previous studies, we deduce also the concentration dependence of these quantities. For e xample, the calculated average atomic volume and bulk modulus of dilut e Li-Mg alloys, as a function of Mg concentration, agree qualitatively very well with experimental results. Furthermore, the pressure depend ence of the lattice distortion is found to be rather important. Our re sults also predict that the solubility of Na in BCC Li under pressure above 50 kbar is possible.