  Based on first-principles simulations and calculations, we explore the
evolution of crystal structure, electronic structure and transport properties
of quasi 2D layered PdS2 under uniaxial stress and hydrostatic pressure. The
coordination of the Pd ions plays crucial roles in the structural transition,
electronic structure and transport properties of PdS2. An interesting
ferroelastic phase transition with lattice reorientation is revealed under
uniaxial compressive stress, which originates from the bond reconstructions of
the unusual PdS4 square-planar coordination. By contrast, the layered structure
transforms to 3D cubic pyrite-type structure under hydrostatic pressure. In
contrast to the experimental proposed coexistence of layered PdS2-type
structure with cubic pyrite-type structure at intermediate pressure range, we
predict that the compression-induced intermediate phase showing the same
structural symmetry with the ambient phase, except of sharply contracted
interlayer-distances. The coordination environments of the Pd ions have changed
from square-planar to distorted octahedra in the intermediate phase, which
results in the bandwidth broaden and orbital-selective metallization. In
addition, the superconductivity comes from the cubic pyrite-type structure
protected topological nodal-line states. The strong correlations between
structural transition, electronic structure and transport properties in PdS2
provide a platform to study the fundamental physics of the interplay between
crystal structure and transport behavior, and the competition between diverse
phases.
