Distortion modes in halide perovskites: to twist or to stretch, a matter of tolerance and lone pairs

Santosh Kumar Radha, Churna Bhandar, Walter R. L. Lambrech

Using first-principles calculations, we show that CsBX${}_3$ halides with B=Sn or Pb undergo octahedral rotation distortions, while for B=Ge and Si, they undergo a ferro-electric rho…