AMBER Archive (2003)

Subject: octahedral volume

From: Peter Varnai (Peter.Varnai_at_ibpc.fr)
Date: Fri Jan 17 2003 - 04:26:58 CST

Dear AMBER list,

I would like to know the volume of a truncated octahedral cell used in a
simulation. The topology file gives the angle (109.471) and some length
parameter. Can someone tell me how this length parameter is related to
the truncated octahedron?
 
When constructing the system, leap reports a volume. This has
been changed between version 6 and 7 according to leap/tools.c:
         dVolume = dMaxX * dMaxY * dMaxZ;
 ver6:
                 dVolume *= 0.5;
 ver7:
                 dVolume *= 0.7698004;
 /* = sqrt(1 - 3*cost^2 - 2*cost^3), where cost = -1/3 = cos(109.471) */
 
Can someone explain where the ver7 formula comes from?
 
Thank you very much for your help.
 
Peter Varnai