Electronic structure and long-period states in Ag3Mg: comparison with Cu-Au alloys

On the basis of ab initio calculations of the electronic structure, an atte mpt is made to identify the reasons for the qualitatively different behavio urs of long-period superstructures (LPS) with large and small superperiods 2M in alloys of noble metals. To this end, analysis is performed of the rel ationship between the nesting properties of the Fermi surface and the struc ture of LPS (of relatively small 2M) formed in the Ag3Mg alloy. The results of the analysis are compared with those obtained earlier for Cu-Au alloys (where LPS possess longer 2M). It is shown that the dependence of the type of LPS on the value of 2M is controlled by the quality of nesting on the Fe rmi surface and the sensitivity of the nesting vector 2 (k) over right arro w (F) to variations in the long-range order parameter.