  Recent experiments have shown that CeH9 and (Ce,La)H9 can be synthesized
under high pressure between 90-170GPa and become a superconductor with a high
value of superconducting critical temperature (Tc) between 100-200K. In this
work, we performed a theoretical study of a (Ce,La)H9 compound where the Ce:La
ratio is equal to 1. We used the density functional theory and the {\it ab
initio} molecular dynamics (AIMD) method. From the phonon dispersion, there
exist some unstable modes around the K-point phonons. Then, we performed AIMD
simulation at around 203K and found that the compound becomes stable. The
superconducting spectral function can be calculated. We found that $\lambda$ is
as high as 3.0 at 200GPa. By using Allen-Dynes-modified McMillan equation in
the strong coupling regime, we found that Tc = 87K at 200GPa.
