![]() ![]() Matter may be positively-charged, negatively-charged or neutral (not charged). We now know those to be negatively-charged electrons. In more controlled experiments, we can observe that charged objects exert invisible forces on one another.īenjamin Franklin, an early researcher in electricity and charge, assigned the label positive to the charges that tend to move the most. We understand charge because we can observe lightning, see sparking between wires and we can get an electric shock when things like fabrics rub together in the dry air of winter. ![]() V&F=Potential and force V=Potential only F=Force only Computing: M-Number M-Flops % Flops Pair Search distance check 1204679.637390 10842116.737 0.9 RF=Reaction-Field VdW=Van der Waals QSTab=quadratic-spline table NB=Group-cutoff nonbonded kernels NxN=N-by-N cluster Verlet kernels Statistics over 5000001 steps using 50001 framesīond Angle Ryckaert-Bell. These options remove COM motion of the system Pcoupltype = isotropic uniform scaling of x-y-z box vectorsĬompressibility = 4.5e-5 isothermal compressibility, bar^-1 Rvdw = 1.0 short-range van der Waals cutoff (in nm) Rcoulomb = 1.0 short-range electrostatic cutoff (in nm) rlist = 1.5 short-range neighborlist cutoff (in nm) Ns_type = grid search neighboring grid cels ![]() constraints = all-bonds all bonds (even heavy atom-H bonds) constrained Nstxout-compressed = 1000 save coordinates in. define = -DPOSRES position restrain the solute ![]() Title = Solute in Water NPT Equilibration Perhaps there is some simple explanation for this? I cannot see how the real space Ewald sum or the direct Coulomb formula can give a negative energy for particles of like charge. I tried PME, Ewald sum, and a simple cut-off and got qualitatively similar results, although a cut-off gives larger values (less negative) for the like ion interactions. My system is simply an OPLS_aa alkane with water and NaCl and when I used energy groups I got this result for the crossed ion interactions: Energy Average Err.Est. Does anyone know why short-range Coulomb energies for cation-cation and anion-anion interactions in an aqueous solution are negative? ![]()
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