COHP method Ca14AlSb11 X-ray diffraction XPS Zintl Zintl compounds alkaline-earth band structure bonding analyses chemical bond coloring problem crystal structure electronic structure group-subgroup intermetallic compounds intermetallics liquid ammonia magnetic properties magnetism nitridometalate plumbides polar intermetallic polar intermetallics powder diffraction stannides structure optimizations symmetry reduction ternary Laves phases thermoelectric total energy