acceleration at high tempreature conditions

Hi, guys
I have a mixture system of H2O and CO2. And I run the same script at two different temperatures, 300K and 973K. The performance is shown as below.

This is for 300K.
Performance: 3.351 ns/day, 7.162 hours/ns, 77.569 timesteps/s
99.4% CPU use with 24 MPI tasks x no OpenMP threads
MPI task timing breakdown:
Section | min time | avg time | max time |%varavg| %total