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<DIV><SPAN class=189191816-02042004><FONT face=Arial color=#0000ff size=2>How
many lambda values are you using?</FONT></SPAN></DIV>
<DIV><SPAN class=189191816-02042004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=189191816-02042004><FONT face=Arial color=#0000ff
size=2>Ilya</FONT></SPAN></DIV>
<DIV><SPAN class=189191816-02042004></SPAN> </DIV>
<BLOCKQUOTE>
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> gmx-users-admin@gromacs.org
[mailto:gmx-users-admin@gromacs.org]<B>On Behalf Of </B>Alexandre Suman de
Araujo<BR><B>Sent:</B> Friday, April 02, 2004 3:26 AM<BR><B>To:</B>
gmx-users<BR><B>Subject:</B> [gmx-users] Bad calculated Free Energy
values<BR><BR></FONT></DIV>Hi GMX-ers!!!<BR><BR>I´m performing some
simulations to obtain free energy of hydration of some ions (Ca+2, Sr+2 and
Ba+2) using oplsaa(tip3p for water) force field and the results aren´t so good
in my opinion. Look at the results below and the experimental values (taken
from book Burgess, <I>Metal Ions in Solution</I>):<BR><BR>DGh
(kJ/mol)<BR><BR>Ion
Calculated
Experimental
Difference<BR><BR>Ca+2 -1391
-1591
200<BR>Sr+2
-1248
-1442
194<BR>Ba+2 -1107
-1317
210<BR><BR><BR>Look that the difference
between calc. and exp. values are something about 200 kJ/mol, then I think
this can be something I´m not including in the calculations that results in
error with almost same values in three cases.<BR><BR>The .mdp file that I´m
using is this one:<BR><BR>;<BR>; Input
file<BR>;<BR>title
= Calculo da energia livre de solvatacao do ion de Na em
H2O ; a
string<BR>cpp
=
/lib/cpp
;
c-preprocessor<BR>dt
=
0.001
; time step
(ps)<BR>integrator
=
md
; Tipo de simulacao a
fazer<BR>nsteps
=
800000
; number of steps<BR>;Faca energia
livre<BR>free_energy =
yes
; calcule a energia
livre<BR>init_lambda =
0
; valor inicial de
lambda<BR>delta_lambda =
1.25e-6
;
1/n_passos<BR>nstcomm
=
1
; reset c.o.m.
motion<BR>nstxout
=
100
; write
coords<BR>nstvout
=
100
; write
velocities<BR>nstlog
=
100
; print to
logfile<BR>nstenergy
=
100
; print
energies<BR>nstlist
=
10
; update
pairlist<BR>ns_type
=
grid
; pairlist
method<BR>pbc
=
xyz
; Usar PBC em todas as
direcoes<BR>rlist
=
1.3
; cut-off for
ns<BR>coulombtype =
Cut-off
; Usa cut-off por causa do calculo de e
livre.<BR>rcoulomb
=
1.3
; cut-off for coulomb<BR>fourierspacing =
0.12
; Parametro pra
PME<BR>pme_order
=
4
; Parametro pra
PME<BR>ewald_rtol
=
1e-5
; Parametro PME<BR>optimize_fft
=
yes
; Optimiza a FFT, claro..
hahah<BR>vdwtype
=
cut-off
; Tipo de
VdW<BR>rvdw
=
1.3
; raio de calculo de
Vdw<BR>tcoupl
=
berendsen
; Temperature
coupling<BR>ref_t
=
300
; Temperatura
referencia<BR>tc-grps
=
System
; Quais grupos sera afetados pelo
tcoupl<BR>tau_t
=
0.01
; Tempo que sera verificada a
temperatura<BR>pcoupl
=
berendsen
; pressure
bath<BR>pcoupltype
=
isotropic
; pressure
geometry<BR>tau_p
=
1
; p-coupoling time<BR>compressibility =
4.4e-5
; compressibilidade da
acetonitrila<BR>ref_p
= 1.0<BR><BR><BR>Somebody could help me telling me if I´m forgetting
anything or making something wrong?<BR>Or this difference is normal in free
energy calculations????<BR><BR>Thank´s very much and waiting answers.<BR><BR><PRE class=moz-signature cols="72">--
Alexandre Suman de Araujo
<A class=moz-txt-link-abbreviated href="mailto:asaraujo@if.sc.usp.br">asaraujo@if.sc.usp.br</A>
UIN: 6194055
IFSC - USP - São Carlos - Brasil</PRE>_______________________________________________
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