  Over the past few years Fe chalcogenides (FeSe/Te) have advanced to the
forefront of Fe-based superconductors (FeBS) research. The most intriguing
results thus far are for intercalated and monolayer FeSe, however experimental
studies are still inconclusive. Yet, bulk FeSe itself remains an unusual case
when compared with pnictogen-based FeBS, and may hold clues to understanding
the more exotic FeSe-derivatives. The FeSe phase diagram is unlike the
pnictides: the orthorhombic distortion, which is likely to be of a
"spin-nematic" nature in numerous pnictides, is not accompanied by magnetic
order in FeSe, and the superconducting transition temperature $T_{c}$ rises
significantly with pressure before decreasing. In this paper we show that the
magnetic interactions in chalcogenides, as opposed to pnictides, demonstrate
unusual (and unanticipated) frustration, which suppresses magnetic, but not
nematic order, favors ferro-orbital order in the nematic phase and can
naturally explain the nonmonotonic pressure dependence of the superconducting
critical temperature $T_{c}(P)$.
