  It is a long-time pursuit of computations with \emph{ab initio} precision of
thermal contributions to phase behaviors of condensed matters under extreme
conditions. In this work, the pressure induced structural phase transitions of
crystalline aluminum up to $600$ GPa at room temperature are investigated based
on the criterion of Gibbs free energy derived directly from the partition
function that formulated in the ensemble theory with the interatomic
interactions characterized by density functional theory computations. The
transition pressures of the FCC$\rightarrow$HCP$\rightarrow$BCC phase
transitions are determined at $194$ and $361$ GPa, the axial ratio of the
stable HCP structure is found to be equal to $1.62$ and the discontinuities in
the equations of states are confirmed to be associated with $-0.67\%$ and
$-0.90\%$ volume changes, which are all in an excellent agreement with the
measurements by one of the recent experiments but differ from other
experimental observations. Compared with the results obtained by the criterion
of enthalpy at $0$K, this work further shows the nontrivial thermal impacts on
the structural stability of aluminum under ultrahigh-pressure circumstances
even at room temperature.
