<div class="im">Hi all,<br><br>I have been trying to calculate the PMF of two NA+ ions
in explicit bulk water. First, I tried to calculate the mean force
between the two ions at a distance of 0.48 nm, which is big enough than
the diameter of the ions. I first energy minimized the system with the
script below, but it did not converge. After that, I removed one of the
ions, and tried again, it did not work again. <br>
<br>I am using ffG43a1 ff, and checked whether I used the correct naming for the ion: Everything seems to be OK. <br><br></div>I could not attach the initial coordinate file due to the limited size. If you want I can also sent it to you as well.<div>
<br><div class="im">
<br><b>Script: </b><br>title = Minimization<br>cpp = /usr/bin/cpp<br>define = -DFLEX_SPC<br>constraints = none<br>integrator = steep<br>dt = 0.002 ; ps !<br>
nsteps = 30000<br>nstlist = 10<br>ns_type = grid<br>rlist = 1.0<br>vdwtype = cut-off <br>coulombtype = PME <br>rcoulomb = 1.0<br>rvdw = 1.4<br>
fourierspacing = 0.12<br>pme_order = 4<br>ewald_rtol = 1e-5<br>optimize_fft = yes<br>;<br>; Energy minimizing stuff<br>;<br>emtol = 100.0<br>emstep = 0.01<br>
<br><br><b>Output</b>:<br><br>Steepest Descents converged to machine precision in 36 steps,<br>but did not reach the requested Fmax < 100.<br>Potential Energy = -1.0409969e+05<br>Maximum force = 9.6685031e+04 on atom 294<br>
Norm of force = 1.4924829e+03<br><br>What may be the problem?<br><br>Best Regards</div></div><br clear="all"><br>-- <br>Ozge Engin<br> ★☆<br>