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<DIV><FONT face=Arial>Thanks for your answer.</FONT></DIV>
<DIV><FONT face=Arial>With the system [166 NIPPA and 4140 water molecules] I
performed runs in three different modalities for the non-bonding interactions,
as described in the following:</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>1)
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"><FONT face="Courier New">;
NEIGHBORSEARCHING PARAMETERS<BR>nstlist<SPAN
style="mso-spacerun: yes">
</SPAN>= 10<BR>ns_type<SPAN
style="mso-spacerun: yes">
</SPAN>= grid<BR>pbc<SPAN
style="mso-spacerun: yes">
</SPAN>= xyz<BR>rlist<SPAN
style="mso-spacerun: yes">
</SPAN>= 0.9</FONT><BR></P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"><FONT face="Courier New">;
OPTIONS FOR ELECTROSTATICS AND VDW<BR>coulombtype<SPAN
style="mso-spacerun: yes">
</SPAN>= PME<BR>rcoulomb-switch<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>rcoulomb<SPAN
style="mso-spacerun: yes">
</SPAN>= 0.9<BR>; Method for doing Van der Waals<BR>vdw-type<SPAN
style="mso-spacerun: yes">
</SPAN>= Cut-off<BR>rvdw-switch<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>rvdw<SPAN
style="mso-spacerun: yes">
</SPAN>= 1.2</FONT></P><FONT face="Courier New"></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT face="Courier New"></FONT>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"><FONT face="Courier New">;
Spacing for the PME/PPPM FFT grid<BR>fourierspacing<SPAN
style="mso-spacerun: yes">
</SPAN>= 0.12<BR>; FFT grid size, when a value is 0 fourierspacing will be
used<BR>fourier_nx<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>fourier_ny<SPAN style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN>=
0<BR>fourier_nz<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>; EWALD/PME/PPPM parameters<BR>pme_order<SPAN
style="mso-spacerun: yes">
</SPAN>= 4<BR>ewald_rtol<SPAN
style="mso-spacerun: yes">
</SPAN>= 1e-05<BR>ewald_geometry<SPAN
style="mso-spacerun: yes">
</SPAN>= 3d<BR>epsilon_surface<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>optimize_fft<SPAN
style="mso-spacerun: yes">
</SPAN>= no</FONT><BR></P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"> </P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"> </P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">2)</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"><FONT face="Courier New">;
NEIGHBORSEARCHING PARAMETERS<BR>nstlist<SPAN
style="mso-spacerun: yes">
</SPAN>= 10<BR>ns_type<SPAN
style="mso-spacerun: yes">
</SPAN>= grid<BR>pbc<SPAN
style="mso-spacerun: yes">
</SPAN>= xyz<BR>rlist<SPAN
style="mso-spacerun: yes">
</SPAN>= 1.0<BR>; OPTIONS FOR ELECTROSTATICS AND VDW<BR>coulombtype<SPAN
style="mso-spacerun: yes">
</SPAN>= reaction_field<BR>rcoulomb-switch<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>rcoulomb<SPAN
style="mso-spacerun: yes">
</SPAN>= 1.5<BR>; Relative dielectric constant for the medium and the reaction
field<BR>epsilon_r<SPAN
style="mso-spacerun: yes">
</SPAN>= 78.5<BR>epsilon_rf<SPAN
style="mso-spacerun: yes">
</SPAN>= 1<BR>vdw-type<SPAN
style="mso-spacerun: yes">
</SPAN>= Cut-off<BR>rvdw-switch<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>rvdw<SPAN
style="mso-spacerun: yes">
</SPAN>= 1.0<BR>; Apply long range dispersion corrections for Energy and
Pressure<BR>dispcorr<SPAN
style="mso-spacerun: yes">
</SPAN>= EnerPres<BR>; Extension of the potential lookup tables beyond the
cut-off<BR>table-extension<SPAN
style="mso-spacerun: yes">
</SPAN>= 1</FONT><BR></P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"><BR> </P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">3) As 1) but with longer
cut-offs</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"><FONT face="Courier New">;
NEIGHBORSEARCHING PARAMETERS<BR>nstlist<SPAN
style="mso-spacerun: yes">
</SPAN>= 10<BR>ns_type<SPAN
style="mso-spacerun: yes">
</SPAN>= grid<BR>pbc<SPAN
style="mso-spacerun: yes">
</SPAN>= xyz<BR>rlist<SPAN
style="mso-spacerun: yes">
</SPAN>= 1.2<BR>; OPTIONS FOR ELECTROSTATICS AND VDW<BR>coulombtype<SPAN
style="mso-spacerun: yes">
</SPAN>= PME<BR>rcoulomb-switch<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>rcoulomb<SPAN
style="mso-spacerun: yes">
</SPAN>= 1.2<BR>vdw-type<SPAN
style="mso-spacerun: yes">
</SPAN>= Cut-off<BR>rvdw-switch<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>rvdw<SPAN
style="mso-spacerun: yes">
</SPAN>= 1.5<BR>; Spacing for the PME/PPPM FFT grid<BR>fourierspacing<SPAN
style="mso-spacerun: yes">
</SPAN>= 0.12<BR>fourier_nx<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>fourier_ny<SPAN style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN>=
0<BR>fourier_nz<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>; EWALD/PME/PPPM parameters<BR>pme_order<SPAN
style="mso-spacerun: yes">
</SPAN>= 4<BR>ewald_rtol<SPAN
style="mso-spacerun: yes">
</SPAN>= 1e-05<BR>ewald_geometry<SPAN
style="mso-spacerun: yes">
</SPAN>= 3d<BR>epsilon_surface<SPAN
style="mso-spacerun: yes">
</SPAN>= 0<BR>optimize_fft<SPAN
style="mso-spacerun: yes">
</SPAN>= no</FONT></P><FONT face="Courier New"></FONT></FONT></DIV>
<DIV><FONT face=Arial>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"> </P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">I observed aggregation in each
case.</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">About the environment control,
temperature had a RMSD of about 2.5 K and pressure of about 185 bar.</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"> </P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">I was reading in the paper
</P>
<DIV id=citation><CITE>J. Phys. Chem. B</CITE>, <SPAN
class=citation_year>2003</SPAN>, <SPAN class=citation_volume>107</SPAN> (35), pp
9424–9433</DIV>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">"Methodological Issues in
Lipid Bilayer Simulations" by Céline Anézo,<A class=ref
href="http://pubs.acs.org/doi/abs/10.1021/jp0348981?journalCode=jpcbfk&quickLinkVolume=107&quickLinkPage=9424&volume=107#jp0348981AF2"><SUP>†</SUP></A>
Alex H. de Vries,<A class=ref
href="http://pubs.acs.org/doi/abs/10.1021/jp0348981?journalCode=jpcbfk&quickLinkVolume=107&quickLinkPage=9424&volume=107#jp0348981AF3"><SUP>‡</SUP></A>
Hans-Dieter Höltje,<A class=ref
href="http://pubs.acs.org/doi/abs/10.1021/jp0348981?journalCode=jpcbfk&quickLinkVolume=107&quickLinkPage=9424&volume=107#jp0348981AF2"><SUP>†</SUP></A>
D. Peter Tieleman,<A class=ref
href="http://pubs.acs.org/doi/abs/10.1021/jp0348981?journalCode=jpcbfk&quickLinkVolume=107&quickLinkPage=9424&volume=107#jp0348981AF4"><SUP>§</SUP></A>
and Siewert-Jan Marrink</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">that the Author modified some
LJ parameters to enhance the hydration of some atoms in their system.</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">I do not know if it is a
legitimate procedure, in my case. If I could obtain the 'right' behaviour of
NIPPA at 293 K, should I be sure to use the same modified parameters at a
different temperature?</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"> </P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">Another idea is to try an
all-atom force field, i.e. OPLS. Do you think anything could change?</P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt"> </P>
<P class=MsoPlainText style="MARGIN: 0cm 0cm 0pt">Ester<BR></P></FONT></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=gmx3@hotmail.com href="mailto:gmx3@hotmail.com">Berk Hess</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=gmx-users@gromacs.org
href="mailto:gmx-users@gromacs.org">Discussion list for GROMACS users</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, February 16, 2010 3:13
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: [gmx-users] undesired
aggregation</DIV>
<DIV><BR></DIV>Hi,<BR><BR>This subject is extremely sensitive to force field
and simulation accuracy.<BR>The small forces driving aggregation are the
result of many, large counteracting forces.<BR>Force fields often give the
right behavior, but nearly never at the correct temperature<BR>unless they
have been explicitly parametrized for this.<BR><BR>I would not expect the
Gromos force field to behave too badly though,<BR>since it has been
parametrized to reproduce partitioning between water and
cyclohexane.<BR><BR>What are your cut-off's and electrostatics
settings?<BR><BR>Berk<BR><BR>
<HR id=stopSpelling>
From: ester.chiessi@uniroma2.it<BR>To: gmx-users@gromacs.org<BR>Date: Tue, 16
Feb 2010 14:35:11 +0100<BR>Subject: [gmx-users] undesired aggregation<BR><BR>
<STYLE>
</STYLE>
<DIV><FONT face=Arial size=2>Hi.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I was trying to simulate the behaviour of
N-isopropyl propionamide, CH3-CH2-CO-NH-CH-(CH3)2 (NIPPA) in aqueous
solution.</FONT></DIV>
<DIV><FONT face=Arial size=2>This molecule has an inverted solubility
behaviour with temperature and it displays a miscibility gap in water for
temperatures higher than about 30°C.</FONT></DIV>
<DIV><FONT face=Arial size=2>Experiments show that at 293 K and 1 atm the
water/NIPPA omogeneous solution phase is stable at any
composition.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I performed a few NPT MD simulations of NIPPA in
water SPC using the 45A3 force field, at different NIPPA concentrations,
293 K (Nose Hoover) and 1 atm (Parrinello Rahman), PME for electrostatic. Two
typical systems contained [288 NIPPA molecules and 1680 water molecules] or
[166 NIPPA and 4140 water molecules].</FONT></DIV>
<DIV><FONT face=Arial size=2>In the starting configuration the NIPPA molecules
were randomly placed and solvated.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I was very surprised to see that after 2 ns
( time step 2 fs) the NIPPA molecules aggregated, in several ways (layer,
cylindrical tube, spherical object) depending on the NIPPA concentration,
whereas I was expecting a complete solubility in water.</FONT></DIV>
<DIV><FONT face=Arial size=2>In a further run at 273 K ( a temperature
about 30 degrees lower than the critical temperature) I found the same
aggregation effect.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>What do you think? Am I beyond the possibilties
of the simulation?</FONT></DIV>
<DIV><FONT face=Arial size=2>Any comment is welcome. Thanks in
advance</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Ester</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>P.S. I found in the literature that the DPPC
self-assembly was modeled in MD simulations ( de Vries et al JACS 2004) at 323
K, a temperature higher than the transition temperature of DPPC. Why did the
Authors use a T where the organized phase is unstable? I was wondering since
also for my system the temperature is a crucial parameter.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Ester Chiessi<BR>Dipartimento di Scienze e
Tecnologie Chimiche<BR>Universitŕ di Roma Tor Vergata<BR>Via della Ricerca
Scientifica<BR>00133 Roma<BR><A
href="http://www.stc.uniroma2.it/cfmacro/cfmacroindex.htm">http://www.stc.uniroma2.it/cfmacro/cfmacroindex.htm</A><BR>tel:
*39*6*72594462</FONT></DIV><BR>
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