  Half-Heusler compounds have emerged as promising thermoelectric materials
that offer huge compositional space to tune their thermoelectric performance. A
class of stable half Heusler compounds formed from elements of three specific
groups in the periodic table viz.
X$_{p}$X$'_{1-p}$Y$_{q}$Y$'_{1-q}$Z$_{r}$Z$'_{1-r}$ (with X, X$'$= Ti, Zr, Hf,
Y, Y$'$ = Ni, Pd, Pt and Z, Z$'$ = Ge, Sn, Pb and p, q, r = 0, 0.25, 0.75 and
1) via various stoichiometric isoelectronic elemental substitution at the X, Y
and Z sites respectively is investigated. Intelligent filters are employed at
each step of our high throughput density functional theory calculations to
filter compounds with improved figure of merit. While confirming several known
results, the calculations also reveal unknown pathways to improve the
thermoelectric performance of the compound class. The 50% X as well as Z site
substitution of the parent Heusler individually are found to marginally enhance
the power factor for both the $p$- and $n$-type doping, while leading to
considerable enhancement in the figure of merit (by $\sim$24 %) specifically
due to lowering of the lattice thermal conductivity because of increase in
lattice disorder in approximately the same cell volume. Furthermore, the
present study confirms the experimental scenario that Y site substitution does
not lead to enhancement of the powerfactor because of the breaking of band
degeneracies at the high symmetry points. This work will serve as a
consolidated cost effective guideline for experimentalist working with this
compound class on enhancing the powerfactor and figure of merit of the
compositions.
