First-row transition metal doped germanium clusters GeM: some remarkable superhalogens.

A theoretical study of geometric and electronic structures, stability and magnetic properties of both neutral and anionic GeM clusters with M being a first-row 3d transition metal atom, is performed using quantum chemical approaches. Both the isoelectronic GeSc anion and neutral GeTi that have a perfect Frank-Kasper tetrahedral shape and an electron shell filled with 68 valence electrons, emerge as magic clusters with an enhanced thermodynamic stability. The latter can be rationalized by the simple Jellium model. Geometric distortions from the Frank-Kasper tetrahedron of GeM having more or less than 68 valence electrons can be understood by a Jahn-Teller effect. Remarkably, DFT calculations reveal that both neutral GeSc and GeCu can be considered as superhalogens as their electron affinities (≥3.6 eV) exceed the value of the halogen atoms and even that of icosahedral Al. A detailed view of the magnetic behavior of GeM clusters shows that the magnetic moments of the atomic metals remain large even when they are quenched upon doping. When M goes from Sc to Zn, the total spin magnetic moment of GeM increases steadily and reaches the maximum value of 3 with M = Mn before decreasing towards the end of the first-row 3d block metals. Furthermore, the IR spectra of some tetrahedral GeM are also predicted.