  The structural phase behaviors of pure zirconium metal under compressions up
to $160$ GPa at room temperature are investigated from the perspective of
ensemble theory where the partition function is solved by our recently proposed
method with \emph{ab initio} precision. The derived Gibbs free energy is
employed as the very criterion to determine phase transitions and the
calculated transition pressures of the
$\alpha\rightarrow\omega\rightarrow\beta$ are $6.93$ and $24.83$ GPa
respectively, the former one of which is so far the only theoretical result
agreeing with multiple experimental measurements to our best knowledge. The
differences between the obtained parameter-free equation of state and those
from latest experiments are less than $1.5\%$ in the whole studied pressure
range, and particularly, within $0.7\%$ when the applied pressure exceeds over
$40$ GPa, the coincidence of which makes us support the argument that the
previously observed anharmonicity-driven isostructural phase transition does
not exist in the $\beta$-phase even though the thermal effects at room
temperature are confirmed to be nontrivial to the phase stability by our
quantitative comparisons with the results at $0$K.
