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In fullerides, the deviation of the superconducting energy gap from BCS prediction, especially close to T_C, in experiments is an old, but not well-understood problem. If phase fluctuations are considered, the calculated temperature temperature of the energy gap is accurately consistent with the experimental one, and the deviation of the gap is a certain result.

The structural stability and electronic properties of ${\mathrm{\text{Ca}}}_{2.75}{\mathrm{\text{C}}}_{60}$ are probed by means of high-pressure Raman spectroscopy using two different pressure transmitting media that lead to practically identical results. Although ${\mathrm{\text{Ca}}}_{2.75}{\mathrm{\text{C}}}_{60}$ is isostructural with the rare-earth metal fulleride, ${\mathrm{\text{Sm}}}_{2.75}{\mathrm{\text{C}}}_{60}$ of the same stoichiometry, the pressure coefficients of characteristic intramolecular ${\mathrm{\text{C}}}_{60}$ modes are larger than those in the ${\mathrm{\text{Sm}}}_{2.75}{\mathrm{\text{C}}}_{60}$ counterpart but similar to those in the pristine ${\mathrm{\text{C}}}_{60}$ solid. Since the reduced pressure coefficients in the Sm fulleride have been attributed to strong $\mathrm{\text{Sm}}\text{-}{\mathrm{\text{C}}}_{60}$ coupling, our findings for the isostructural Ca fulleride are compatible with a reduced orbital mixing and $\mathrm{\text{Ca}}\text{-}{\mathrm{\text{C}}}_{60}$ coupling.