CHEMICAL TRENDS IN GOLD ALKALI ALLOYS - A DFT-STUDY ON STABILITY AND CHARGE-TRANSFER .2. GOLD ALKALI ALLOYS OF THE FORMULA MAU(5)

Gold alkali alloys of the formula MAu(5) have not roused the same inte rest as the gold alkali alloys of the formula MAu. Only 30 years after their discovery by Kienast and Verma, single crystal data for KAu5 an d RbAu5 first became available. Until now all further efforts to synth esize NaAu5 and CsAu5 failed; moreover, there have been no theoretical investigations in these systems. Within the framework of density func tional theory (DFT) (with the local density approximation (LDA) and no rm-conserving, scalar-relativistic pseudopotentials) we focus our inte rest on the stability of the class of MAu(5) compounds. For that purpo se we consider the experimental and hypothetical compounds with theore tical calculations, by determining the equilibrium unit cell volumes a nd the lattice constants and by investigating the valence charge trans fer. We present results concerning the stability of MAu(5) compounds w ith special emphasis on the unknown phases NaAu5 and CsAu5.