  We propose a possible charge fluctuation effect expected in layered
superconducting materials. In the multireference density functional theory,
relevant fluctuation channels for the Josephson coupling between
superconducting layers include the interlayer pair hopping derived from the
Coulomb repulsion. When interlayer single-electron tunneling processes are
irrelevant in the Kohn-Sham electronic band structure calculation, the two-body
effective interactions stabilize a superconducting phase. This state is also
regarded as a valence-bond solid in a bulk electronic state. The hidden order
parameters coexist with the superconducting order parameter when the charging
effect of a layer is comparable to the pair hopping. Relevant materials
structures favorable for the pair-hopping mechanism are discussed.
