Engineering superconductors with ab initio methods: ternary metal borides

We have performed a targeted search for novel superconducting ternary borides starting from the recently identified class of binary metal sandwich (MS) structures [1]. Our {\it ab initio} calculations suggest that a theoretically-devised MS lithium monoboride gains in stability when alloyed with electron-rich metals [2,3]. In an effort to pre-select compounds with the strongest electron-phonon coupling we evaluate the softening of the in-plane boron phonon mode in a large class of metal borides. Our results reveal interesting general trends for the frequency of the in-plane boron phonons as a function of the boron-boron bond length and the valence of the metal [4]. Research supported by ONR and NSF. [1] PRB 73, 180501(R) (2006) [2] PRB 74, 224507 (2006). [3] PRB 75, 144506 (2007) [4] A.N. Kolmogorov, M. Calandra, S. Curtarolo, submitted to PRB.