  We propose a quantum-mechanical dimensionless metric, the local$-$lattice
distortion (LLD), as a reliable predictor of ductility in refractory
multi-principal-element alloys (RMPEAs). The LLD metric is based on
electronegativity differences in localized chemical environments and combines
atomic$-$scale displacements due to local lattice distortions with a weighted
average of valence$-$electron count. To evaluate the effectiveness of this
metric, we examined body$-$centered cubic (bcc) refractory alloys that exhibit
ductile$-$to$-$brittle behavior. Our findings demonstrate that local$-$charge
behavior can be tuned via composition to enhance ductility in RMPEAs. With
finite$-$sized cell effects eliminated, the LLD metric accurately predicted the
ductility of arbitrary alloys based on tensile$-$elongation experiments. To
validate further, we qualitatively evaluated the ductility of two refractory
RMPEAs, i.e., NbTaMoW and Mo$_{72}$W$_{13}Ta$_{10}Ti$_{2.5}Zr$_{2.5}, through
the observation of crack formation under indentation, again showing excellent
agreement with LLD predictions. A comparative study of three refractory alloys
provides further insights into the electronic-structure origin of ductility in
refractory RMPEAs. This proposed metric enables rapid and accurate assessment
of ductility behavior in the vast RMPEA composition space.
