[gmx-users] g_wham -sym question

[ANDRES ADOLFO ORTEGA GUERRERO]

hi dear Gromacs User,
i was wondering if you could help me with something,

I made a set of Umbrella sampling simulation of a Drug passing through a
POPC membrane, i use Gromacs 5.0 rc1, i use the geometry direction ,
when i use

g_wham -it tpr-files.dat -if pullf-files.dat -unit kCal -ac -bs-method hist
-nBootstrap 50
i get a PMF when the first umbrella simulation the energy is set to 0, and
continuing decreasing, i read that for membranes it is important to use
-sym, but when i use it, my PMF dont start with 0 energy? is this a bug? or
what could be my mistake? this -sym should always be use for membranes?
should be used for ion channels too? or
it is due to the pull-geometry?

thank you in advance

Andrés