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<DIV><FONT face=Arial size=2>Hi all.<BR>I’m trying FEP In gromacs3.3. My
system (3nm; 3nm; 3nm) consists <BR>of one Na, Cl, DUM ion and solvent
molecules. <BR> During my free energy calculations I want to perturb:<BR>1)
Cl- into a DUM atom<BR>2) DUM into
Cl-</FONT></DIV>
<DIV> </DIV><FONT face=Arial size=2>
<DIV><BR>I’m using ffgmx. I’ve added new atom DUM into
ffgmx.atp:<BR>…..<BR> SD 32.06000 ;
DMSO Sulphur<BR> OD 15.99940 ; DMSO
Oxygen<BR> CD 15.03500 ; DMSO
Carbon<BR> CHE 12.01100 ; HEME RING
CARBON<BR> MNH3 0
; Dummy mass in rigid tetraedrical NH3
group<BR> MW 0
; Dummy mass in rigid tyrosine rings<BR>
IW 0 ;
Dummy particle in TIP4P etc.<BR> DUM
0 ; moj
atom<BR>…..</DIV>
<DIV> </DIV>
<DIV>I’ve updated ffgmxnb.itp:<BR>….<BR>OWT3
15.99940
0.000 A 0.24889E-02
0.24352E-05<BR> SD
32.06000
0.000 A 0.10561E-01
0.21499E-04<BR> OD
15.99940
0.000 A 0.22715E-02
0.75147E-06<BR> CD
15.03500
0.000 A 0.90507E-02
0.21758E-04<BR> CHE
12.01100
0.000 A 0.23402E-02
0.33740E-05<BR> MNH3
0
0.000 A
0.0
0.0<BR> MW
0
0.000 A
0.0 0.0<BR>
DUM
0
0.000 A
0.0 0.0<BR>….</DIV>
<DIV> </DIV>
<DIV>My dual topology for Cl and DUM atoms:</DIV>
<DIV> </DIV>
<DIV>[ moleculetype ]<BR>; molname
nrexcl<BR>Cl
1</DIV>
<DIV> </DIV>
<DIV>[ atoms ]<BR>; id at type res nr residu
name at name cg nr
charge<BR>1
DUM 1
DUM
DUM 1
0 35.45300 Cl
-1 35.45300</DIV>
<DIV> </DIV>
<DIV><BR>… and </DIV>
<DIV> </DIV>
<DIV>[ moleculetype ]<BR>; molname
nrexcl<BR>ClB
1</DIV>
<DIV> </DIV>
<DIV>[ atoms ]<BR>; id at type res nr residu
name at name cg nr
charge<BR>1 Cl
1
Cl
Cl 1
-1 35.45300 DUM
0 35.45300</DIV>
<DIV> </DIV>
<DIV><BR>I did calculations for 20 lambda values 0.05, 0.10 , 0.15
….<BR> 0.95 and for those values delta free energy looks reasonable.<BR>My
problem is that I get error every time I try to run <BR> FEP for lambda = 1
or lambnda = 0.<BR>Am I doing something wrong. Please give me some advice.
<BR> (I’m using PME, DUM and Cl atom are restrained, step 1fs)</DIV>
<DIV> </DIV>
<DIV><BR>My ERROR message for lambda = 0 is :<BR>…<BR>….</DIV>
<DIV> </DIV>
<DIV> Large VCM(group Cl):
-38.08457, 8.92837, -19.97197,
ekin-cm: 6.83899e+04<BR>Large VCM(group Na):
0.04709, -0.21100, -0.29647,
ekin-cm: 1.54762e+00</DIV>
<DIV> </DIV>
<DIV>t = 0.002 ps: Water molecule starting at atom 61 can not be
settled.<BR>Check for bad contacts and/or reduce the timestep.Wrote pdb files
with previous and current coordinates<BR>Large VCM(group
SOL): -0.01922,
-0.00999, -0.02540, ekin-cm: 8.98334e+00<BR>Large
VCM(group Cl):
4.35556, 2.33494,
5.86521, ekin-cm: 2.08547e+03<BR>Large VCM(group
Na): 0.04590,
-0.19717, -0.27716, ekin-cm: 1.35412e+00<BR>Large
VCM(group SOL): -0.05937,
0.00317, -0.07617, ekin-cm: 7.52736e+01<BR>Large
VCM(group Cl): 13.48634,
-0.66233, 17.40376, ekin-cm: 1.72022e+04<BR>Large
VCM(group Na): 0.04470,
-0.18096, -0.25439, ekin-cm: 1.14329e+00<BR>Large
VCM(group SOL): -0.00393,
-0.03332, 0.01434, ekin-cm:
1.07341e+01<BR>Large VCM(group Cl):
0.88076, 7.63229,
-3.18263, ekin-cm: 2.45181e+03</DIV>
<DIV> </DIV>
<DIV>t = 0.003 ps: Water molecule starting at atom 631 can not be
settled.<BR>Check for bad contacts and/or reduce the timestep.Wrote
pdb<BR> files with previous and current coordinates<BR>Large VCM(group
Cl): 6.73354,
14.12955, -14.62614, ekin-cm: 1.62697e+04</DIV>
<DIV> </DIV>
<DIV><BR>Thank you for your help<BR>ALL BEST<BR></FONT></DIV></BODY></HTML>