\emph{Ab initio} Prediction of Yield-Stress Anomalies in L$1_2$ Ni$_{3}$Ge-Fe$_{3}$Ge Psuedo-Binaries

L1$_{2}$-based (Ni$_{1-c}$Fe$_{c}$)$_{3}$Ge is an ideal system to study yield-strength anomaly and its origin as it is a continuous solid-solution versus \textit{c}, and Ni$_{3}$Ge exhibits an anomaly while Fe$_{3}$Ge does not. We calculated planar-fault energies, i.e. antiphase boundaries (APB) and generalized stacking faults as a function of \textit{c}. We predict to loss of yield-strength anomaly via an energy-based, \emph{necessary} condition using APB energy anisotropy and elastic anisotropy in combination with a \emph{sufficiency} condition that APB(111) is stable against formation of a superlattice intrinsic stacking fault. We predict the transition from anomalous to normal temperature dependence of yield strength for $c\ga0.35$ (or 26 $at.\%$ Fe), as is observed. The APB energies agree quantitatively with experimentally assessed values when antisite disorder (either thermal or off-stoichiometric), which is intrinsic to the characterization data, is taken into account. *Support through the DOE at the Frederick Seitz Materials Research Laboratory (DEFG02-91ER45439), and the NSF at the Materials Computation Center (DMR-0312448)