  Triboelectricity has been known since antiquity, but the fundamental physics
underlying this phenomenon lacks consensus. We present a flexoelectric model
for triboelectricity where contact deformation induced band bending is the
driving force for charge transfer. This framework is combined with first
principles and finite element calculations to explore charge transfer
implications for different contact geometry and materials combinations. We
demonstrate that our ab initio based formulation is compatible with existing
empirical models and experimental observations including charge transfer
between similar materials and size/pressure dependencies associated with
triboelectricity.
