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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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