[gmx-users] EM in vacuum
lindahl at stanford.edu
Fri Feb 21 09:54:37 CET 2003
Gromacs actually adds the -FLEX_SPC option automatically for you when
using cg (as far as I remember).
The reason why need it is that the normal water models like SPC and
TIP3P are rigid, so even if the force was 1e+127 it wouldn't change the
water geometry (but the integration would of course crash). To avoid
this, we remove the rigidity during energy minimization and allow the
bonds and angles to change. When you start the real dynamics run (from
a minimized conformation) the molecule will be reset to its rigid state
So, in short, unless you have water (molecules with SETTLE statements
in general) you can forget about it.
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