[gmx-users] Total Kinetic Energy And Rotational And Translational Kinetic Energy

[Size Zheng]

Hi, there,

I am doing a very simple case of a ice cubic box. 

I would like to use g_energy to investigate the total kinetic energy of the system and use g_traj to generate the rotational and translational kinetic energy separately, by -ekr and -ekt flags. However I found that the sum of the rotational and translational kinetic energy is not equal to the generated total kinetic energy. 

At first I thought this might be because the temperature was so low and constricted the motions of molecules, then I made a new system of a water cubic box in 300 K. However, the result was the same, i.e. the total KE and the sum of rotational KE and translational KE was not the same, and actually their gap was kind of large. 

I totally have no idea about this. Is there something wrong or something I missed?

Many thanks,

Size Zheng