From: Ajasja Ljubetič (ajasja.ljubetic_at_gmail.com)
Date: Tue May 17 2011 - 12:27:50 CDT

The keywords are

   - *useFlexibleCell *

   - *useConstantArea*

http://www.ks.uiuc.edu/Research/namd/2.8b2/ug/node37.html
<http://www.ks.uiuc.edu/Research/namd/2.8b2/ug/node37.html>Regards,
Ajasja

PS: don't forget to go through the NAMD membrane tutorial.
http://www.ks.uiuc.edu/Training/Tutorials/science/membrane/mem-tutorial.pdf