Hi all,
I am doing preliminary minimizations on a relatively small solvated
system. When the system is built with TIP3P waters, the minimization
proceeds more or less as expected, but if I build the system with TIP4P-Ew
waters the electronic energy goes off to negative infinity (****
behavior). Also, after the first 100 steps or so the max force at each
step becomes "fixed" on a specific TIP4P-Ew hydrogen, oscillating back and
forth by ~10 kcal/mol-A. By the time cycles run out the bonding structure
of that water (which is near the boundary if that is relevant) is badly
deformed from it's starting configuration. This happens reproducibly.
Relevant lines from the tleap scripts (commented lines were switched in
either build):
source leaprc.ff10
#loadamberparams frcmod.tip4pew
#loadamberparams frcmod.ionsjc_tip4pew
#WAT = T4E
loadamberparams frcmod.ionsjc_tip3p
(load pre-solvated pdb made using VMD solvate box and TIP3P water, etc.)
Minimization input (I just realized the ewald part is pointless, but I
originally copied and pasted from another MD input):
Minimization to remove bad contacts
&cntrl
imin = 1, ncyc = 1000, maxcyc = 1000,
ntr = 1, restraint_wt = 250.0, restraintmask = ':1-22', ! restrain all
ion and solute residues
cut = 10
/
&ewald
ew_type = 0, order = 6,
nfft1 = 50, nfft2 = 50, nfft3 = 50
/
I've successfully "converted" TIP3P boxes to TIP4P-Ew boxes before, so I
don't think that's the problem (does anyone vehemently disagree?). The
objective here was to compare the different solvation effects from the 2
water models, so building a new box does not really help.
Thanks,
Brian
--
================================ Current Address =======================
Brian Radak : BioMaPS
Institute for Quantitative Biology
PhD candidate - York Research Group : Rutgers, The State
University of New Jersey
University of Minnesota - Twin Cities : Wright-Rieman Hall 101
Graduate Program in Chemical Physics : 610 Taylor Road,
Department of Chemistry : Piscataway, NJ
08854-8066
radak004.umn.edu :
radakb.biomaps.rutgers.edu
====================================================================
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Received on Thu Nov 03 2011 - 09:00:04 PDT
