There is a strange phenomena when I do Langevin dynamics. See the
Figure attached, The center of mass of my studying object shift from
postive to negative abruptly though the volecity of c.m. is postive.
Why? Is there a bug in fix langevin command?
Note, I have checked the efield is small sufficiently not to change
the size of radius of gyration of object.
my in code is presented as follows.