[MMTK] Ewald sums.

Adam Hixson chixson@chemdept.chem.ou.edu
Sun, 9 Sep 2001 13:49:55 -0700 (PDT)

I created a box of water using MMTK v2.2b6 using
the following code:

from MMTK import *
from MMTK.ForceFields import Amber94ForceField
from MMTK.Random import randomPointInBox
from MMTK.Solvation import *

size = 30.*Units.Ang

universe = CubicPeriodicUniverse(size,
Amber94ForceField(size / 2.5,None))
print "...and let there be a universe."
print "Solvent added, and now shrinking..."
print "Done...and saved."

But when I load this universe and try to evaluate
the energy, it gives a value that is very large.

For example, after loading python:
>>> from MMTK import *
>>> universe = load("water.univ")
>>> universe.energy()
>>> from MMTK.ForceFields import Amber94ForceField
>>> universe.energy()


Doing away with the Ewald sums, and setting a cutoff
gives a more reasonable result.

I am fairly new to MD, and have never used Ewald sums
before, so I may be naively doing somthing bone-
headed.  What might cause this result?

Adam Hixson
Department of Chemistry and Biochemistry
The University of Oklahoma     chixson@chemdept.chem.ou.edu
620 Parrington Oval            hixsonc@yahoo.com
Norman, OK 73069

Do You Yahoo!?
Get email alerts & NEW webcam video instant messaging with Yahoo! Messenger