  Robust metallic surface states (MSS) of topological insulator (TI) against
imperfections and perturbations are important in broad applications such as
chemical catalysis and quantum computing. Unfortunately, they are suffered from
the narrow band gap that can be accessed. Searching for MSS with large bulk
band gap beyond conventional TIs becomes a quest. In this work, inspired by the
adiabatic connection principle in real space, we identify that all electrides,
a new class of emerging materials, must host robust and universal MSS that
resists any disturbances, in spite of the fact that some of them could be
classified as trivial in standard topology theory. This counterintuitive
property is traced to the specific charge localization-delocalization change
intrinsic to electride when approaching the crystalline surface or interface,
which is a kind of interstice-centered to atom-centered transition in the
real-space topology of the charge density distribution, and is sharply
different from the band inversion in the standard topology theory. The new
mechanism circumvents the obstacle that limits the band gap of TI. Robust and
universal MSS in an electride that conventionally-determined as trivial but
with a colossal band gap beyond 6.13 eV are demonstrated. This gap size is
about 6-fold larger than the highest record of known "wide-gap" TIs, thus opens
up new avenues to universal MSS with gigantic bulk gap.
