<html><div style='background-color:'><DIV class=RTE>Dear all,</DIV>
<DIV class=RTE>i have a problem concerning a MD simulation on a small RNA structure.</DIV>
<DIV class=RTE>I have minimized the structure in vacum reaching the following result:</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE> Step Time Lambda<BR> 627 627.00000 0.00000</DIV>
<DIV class=RTE> Energies (kJ/mol)<BR> Bond Angle Proper Dih. Ryckaert-Bell. LJ-14<BR> 2.45163e+02 6.40761e+02 3.78574e+00 1.76619e+03 7.44530e+02<BR> Coulomb-14 LJ (SR) Coulomb (SR) Coul. recip. Potential<BR> -1.23051e+04 -1.46899e+03 -1.82476e+03 3.01441e+03 -9.18396e+03<BR> Kinetic En. Total Energy Temperature Pressure (bar)<BR> 0.00000e+00 0.00000e+00 0.00000e+00 0.00000e+00</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>The structure semms pretty good, but when I add water (ffamber_tip4p) to run the energy minimization in the solvent box the LJ (SR) shows to very high values also at the end of minimization:</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE><BR> Step Time Lambda<BR> 0 0.00000 0.00000</DIV>
<DIV class=RTE> Energies (kJ/mol)<BR> Bond Angle Proper Dih. Ryckaert-Bell. LJ-14<BR> 2.67813e+02 6.44749e+02 3.98629e+00 1.76818e+03 7.42894e+02<BR> Coulomb-14 LJ (SR) Coulomb (SR) Coul. recip. Potential<BR> -1.23031e+04 6.22337e+04 -2.70809e+05 -3.59886e+04 -2.53439e+05<BR> Kinetic En. Total Energy Temperature Pressure (bar)<BR> 0.00000e+00 0.00000e+00 0.00000e+00 0.00000e+00</DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE> Step Time Lambda<BR> 2031 2031.00000 0.00000</DIV>
<DIV class=RTE> Energies (kJ/mol)<BR> Bond Angle Proper Dih. Ryckaert-Bell. LJ-14<BR> 2.62036e+02 7.38608e+02 9.55040e+00 1.74683e+03 7.08018e+02<BR> Coulomb-14 LJ (SR) Coulomb (SR) Coul. recip. Potential<BR> -1.23454e+04 5.91634e+04 -3.68597e+05 -4.18478e+04 -3.60162e+05<BR> Kinetic En. Total Energy Temperature Pressure (bar)<BR> 0.00000e+00 0.00000e+00 0.00000e+00 0.00000e+00 </DIV>
<DIV class=RTE> </DIV>
<DIV class=RTE>Then, if I try to run a position restrain or a simulated annealing on the minimized sistem I observe a very high pressure value and sistem crush after few iterations.</DIV>
<DIV class=RTE>What could I do?</DIV>
<DIV class=RTE>Do you think that to lower the system density, to increase the box size or change water topology (ffamber_tip3p) may be good way to overcome the problem?</DIV>
<DIV class=RTE>Bests,</DIV>
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