# [gmx-users] Electric potential over the membrane

David spoel at xray.bmc.uu.se
Sat Nov 22 11:36:01 CET 2003

```On Sat, 2003-11-22 at 11:23, Itamar Kass wrote:
>     I have periodic boundary, and the size of the box is
> ~6.2*6.2*6.7.  Follow from your explain I understand I have to write E_z =
> 1  15  0.0 the results potential will be 15mV/nm*6.7nm=~100mV?
except for a factor 1000, the unit is V/nm, so it should be 0.015

Take care however that you should calculate the potential over your
membrane, not the box, so again for a 3 nm membrane with 100 mV you'd
want to use

1 0.033 0.0

--
David.
________________________________________________________________________
David van der Spoel, PhD, Assist. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

```