  The 1144 iron arsenide (e.g. CaKFe4As4) has recently been discovered and
inspired a tide of search for superconductors. Such far, the discovered
compounds are confined to iron arsenides (ABFe4As4), where A and B are either
alkali metals or alkaline earth elements. In this work, we propose two
directions in searching 1144 structures: (i) using tri-valence cations for A;
(ii) substituting the transition metal, e.g. replacing Fe by Co. Following the
two directions, we employ density functional theory to study stability and
electronic structures of 1144 pnictides of various tri-valence cations (La, Y,
In, Tl, Sm and Gd), as well as cobalt arsenides. For LaAFe4As4, the 1144 phase
can be stabilized in three systems: LaKFe4As4, LaRbFe4As4 and LaCsFe4As4, which
show quasi-two-dimensional semi-metal features similar to the iron pnictide
superconductors: hole-type Fermi surface at Gama point and electron-type Fermi
surface at M point in B.Z. In addition, LaKFe4As4 feature an extra bubble
shaped Fermi surface sheets, distinct from the other two peers. Y does not
support any 1144 phase within our search. For In and Tl, substitute Fe by Co
and two unknown compounds of the 122 phase are stabilized: InCo2As2 and
TlCo2As2. The two cobalt arsenides have Fermi surfaces of similar topology as
iron arsenides, but the Fermi surfaces are all electron-type, showing
potentials to be undiscovered superconductors. Stable 1144 phases are also
found in InKCo4As4 and InRbCo4As4. For Sm and Gd, most 1144 and 122 iron
arsenides are found unstable.
