<html><div style='background-color:'><DIV class=RTE>Dear all,</DIV>
<DIV class=RTE>I'm tryng to carry out a MD simulation on a small RNA fragment using ffamber94 in gromacs 3.3.1.</DIV>
<DIV class=RTE>I've modified my PDB file (as described at the web page <A href="http://folding.stanford.edu/ffamber/">http://folding.stanford.edu/ffamber/</A>) and converted it in Gormacs format using pdb2gmx. Then I've solvated my system using editconf (cubic) and genbox (ffamber_tip4p) commads. To neutralize system charge I've added 21 Na+ using genion command. I've minimized the resulting system using the following mdp file.</DIV>
<DIV class=RTE> <BR>define = -DFLEX_SPC<BR>constraints = none<BR>integrator = steep<BR>dt = 0.002 ; ps !<BR>nsteps = 10000<BR>nstlist = 10 <BR>ns_type = grid<BR>rlist = 0.9<BR>coulombtype =
PME<BR>rcoulomb = 0.9<BR>rvdw = 0.9<BR>fourierspacing = 0.12<BR>fourier_nx = 0<BR>fourier_ny = 0<BR>fourier_nz = 0<BR>pme_order = 6<BR>ewald_rtol = 1e-5<BR>optimize_fft = yes<BR>;<BR>; Energy minimizing stuff<BR>;<BR>emtol = 100.0<BR>emstep = 0.1</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>The minimization was converged after 740 steps and the generated structure look pretty good.</DIV>
<DIV class=RTE>Starting from this structure, to equilibrate solvent, I 've tryed to run a position restrain using the following parameters:</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>define = -DPOSRES<BR>constraints = all-bonds<BR>integrator = md<BR>dt = 0.002 ; ps !<BR>nsteps = 10000 ; total 20.0 ps.<BR>nstcomm = 1<BR>nstxout = 250<BR>nstvout =
1000<BR>nstfout = 0<BR>nstlog = 10<BR>nstenergy = 10<BR>nstlist = 10 <BR>ns_type = grid<BR>rlist = 0.9<BR>coulombtype = PME<BR>rcoulomb = 0.9<BR>rvdw = 0.9<BR>fourierspacing = 0.12<BR>fourier_nx =
0<BR>fourier_ny = 0<BR>fourier_nz = 0<BR>pme_order = 6<BR>ewald_rtol = 1e-5<BR>optimize_fft = yes<BR>; Berendsen temperature coupling is on in two groups<BR>Tcoupl = berendsen<BR>tc-grps = Protein SOL Na+ <BR>tau_t = 0.1 0.1 0.1<BR>ref_t = 300 300 300<BR>; Pressure coupling is on<BR>Pcoupl =
berendsen<BR>pcoupltype = isotropic<BR>tau_p = 1.0<BR>compressibility = 4.5e-5<BR>ref_p = 1.0<BR>; Generate velocites is on at 300 K.<BR>gen_vel = yes<BR>gen_temp = 300.0<BR>gen_seed = 173529<BR></DIV>
<DIV class=RTE>During the grompp I've obtained the following WARNING message for the lines 426, 428, 429, 432 and 441:</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>/usr/local/gromacs/share/gromacs/topffamber94bon.itp:426:22: warning: ISO C reqires whitespace after the macro name</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>This message refer to the * position in these lines of ffamber94bon.itp file:</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>; missing nucleic torsions<BR>#define proper_X_CT_N*_X 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000<BR>#define proper_X_CM_CT_X 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000<BR>#define proper_X_CK_N*_X 14.22560 0.00000 -14.22560 0.00000 0.00000 0.00000<BR>#define proper_X_CB_N*_X 13.80720 0.00000 -13.80720 0.00000 0.00000 0.00000<BR>#define proper_X_CA_NC_X
40.16640 0.00000 -40.16640 0.00000 0.00000 0.00000<BR>#define proper_X_CQ_NC_X 56.90240 0.00000 -56.90240 0.00000 0.00000 0.00000<BR>#define proper_X_C_N*_X 12.13360 0.00000 -12.13360 0.00000 0.00000 0.00000<BR>#define proper_X_CM_CM_X 55.64720 0.00000 -55.64720 0.00000 0.00000 0.00000<BR>#define proper_X_C_NC_X 33.47200 0.00000 -33.47200 0.00000
0.00000 0.00000<BR>#define proper_X_CA_CM_X 21.33840 0.00000 -21.33840 0.00000 0.00000 0.00000<BR>#define proper_X_C_NA_X 11.29680 0.00000 -11.29680 0.00000 0.00000 0.00000<BR>#define proper_X_CA_NA_X 12.55200 0.00000 -12.55200 0.00000 0.00000 0.00000<BR>#define proper_X_CK_NB_X 83.68000 0.00000 -83.68000 0.00000 0.00000 0.00000<BR>#define proper_X_C_CM_X 18.20040
0.00000 -18.20040 0.00000 0.00000 0.00000<BR>#define proper_X_CA_N2_X 20.08320 0.00000 -20.08320 0.00000 0.00000 0.00000<BR>#define proper_X_N*_CM_X 15.48080 0.00000 -15.48080 0.00000 0.00000 0.00000</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>What I have to do?</DIV>
<DIV class=RTE>Ignoring the warning, position restrain give the following warning :</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>Step 6, time 0.012 (ps) LINCS WARNING</DIV>
<DIV class=RTE>relative costraint deviation after LINCS:</DIV>
<DIV class=RTE>max 0.001535 (between atoms 85 and 86) RMS 0.000106</DIV>
<DIV class=RTE>bond that rotated more than 30 degrees:</DIV>
<DIV class=RTE> atom 1 atom 2 angle previous, current, constraint length</DIV>
<DIV class=RTE> 565 566 33.3 0.1010 0.1010 0.1010</DIV>
<DIV class=RTE>.</DIV>
<DIV class=RTE>.</DIV>
<DIV class=RTE>and so on.</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>Looking at the structures in trajectory file it is possible observe a total distortion of RNA structure.</DIV>
<DIV class=RTE>Then to overcome the problem I've tried to run a simulated annealing taking the RNA fixed:</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>constraints = all-bonds<BR>integrator = md<BR>dt = 0.002 ; 1000 ps !<BR>nsteps = 500000<BR>nstcomm = 1<BR>nstxout = 500<BR>nstvout = 500<BR>nstfout = 0<BR>nstlist = 10
<BR>ns_type = grid<BR>rlist = 0.9<BR>coulombtype = PME<BR>rcoulomb = 0.9<BR>rvdw = 0.9<BR>fourierspacing = 0.12<BR>fourier_nx = 0<BR>fourier_ny = 0<BR>fourier_nz = 0<BR>pme_order = 6<BR>ewald_rtol = 1e-5<BR>optimize_fft = yes<BR>; Berendsen temperature coupling is on in three groups<BR>Tcoupl =
berendsen<BR>tau_t = 0.1 0.1 0.1<BR>tc-grps = protein SOL Na+<BR>ref_t = 0 300 300<BR>; Pressure coupling is on<BR>Pcoupl = berendsen<BR>pcoupltype = isotropic<BR>tau_p = 1.0<BR>compressibility =
4.5e-5<BR>ref_p = 1.0<BR>; Generate velocites is on at 300 K.<BR>gen_vel = yes<BR>gen_temp = 0</DIV>
<DIV class=RTE>annealing = single single single<BR>annealing_npoints = 2 11 11 <BR>annealing_time = 0 1000 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500<BR>annealing_temp = 0 0 0 30 60 90 120 150 180 210 240 270 300 0 30 60 90 120 150 180 210 240 270 300 </DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>The results are almost the same.</DIV>
<DIV class=RTE>How can I do to equilibrate and simulate my system?</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>I am sorry for the length of my post.</DIV>
<DIV class=RTE>Thanks in advance for all suggestions.</DIV>
<DIV class=RTE><FONT face="Lucida Handwriting, Cursive"></FONT> </DIV>
<DIV class=RTE><FONT face="Lucida Handwriting, Cursive">Sara Pistolesi</FONT></DIV></div></html>