  Under the weak coupling, we investigate the critical temperatures under
pressure of H3S, LaH10, CaH6, and Tl2Ba2CaCu2O8+{\delta} superconductors. The
superconducting mechanism takes into account the electron-phonon interaction as
well as the Coulomb interaction. Under high pressure, the critical temperature
equation is calculated as a function of the fractional volume of the unit cell,
and the Birch-Murnaghan equation of state is used to determine the relationship
between fraction volume and pressure. Using this equation, we can analyze the
parabolic-like relationship between the critical temperature and pressure of a
superconductor. The parabolic behavior of these superconductors' critical
temperature versus pressure can fit well. The maximal critical temperature of
Tl2Ba2CaCu2O8+{\delta}, H3S, LaH10, and CaH6 superconductors are predicted to
be 112 K at 7 GPa, 197 K at 140 GPa, 252 K at 143 GPa, and 207 K at 174 GPa,
respectively.
