Yes, this is possible but will require some script writing. The value of the electric field in each cell can be obtained by subtracting neighboring grid point values and dividing by the grid spacing in the relevant direction.
The fields you see in VMD are calculated by the VMD program from APBS potentials using the method I described.
Pacific Northwest National Laboratory
From: Neil Sapra <nvsapra@...>>
Date: Friday, June 21, 2013 2:03 PM
To: APBS-USERS mailing list <apbs-users@...>>
Subject: [apbs-users] Obtaining Electric Fields
Hello, I was wondering if it is possible to get the electric field vectors at each point on the grid from the electrostatic potential pot.dx file.
It seems that when APBS is computing the fields for visualization on VMD it is doing so on the fly. But is the result of the calculation stored in some file? If not, am I best off writing some script that will compute the gradient of the pot.dx file or is there an in-built feature that does this in APBS?