Dear all,
I need help for doing minization in LAMMPS. I want to fix the distance between two atoms ( non-bonded atoms) and minimize the other atoms for many values of this distance. I tried alot, but couldn’t suceed. Can somebody help me ?
Eg: i have two ethanols. I want to fix the C-C distance and do minimization as a function of this distance.
Thanks in advance.
Regards,
Sandeep
There are many, many kinds of constrained opt,
and LAMMPS doesn't try to do any of them. If your
2 atoms are not too far apart, you can try putting
a stiff bond between them, and then do a minimize.
That will keep them close to a fixed distance apart.
In general, constrained opt, is a different mathematical
beast than unconstrained.
Steve
Dear Steve,
Thanks for the reply. As Axel reply me, i tried setting the forces on two atoms to zero. This option seems to give me reasonable results.
I am confused now. Can you help me how to know whether this results are right or wrong ?
Regarding using stiff bond between two atoms, as i am interested to vary this to large distances (upto 10A), this option might not help. (i tried this option before posting it to mailing list)
Regards,
Sandeep
Nailing the 2 atoms to their original positions is not the same
thing as holding the distance between them constant. The former
can be done with setting the force on them to 0.0. The
latter is true constrained optimization and would allow them
to more together (e.g. rotate) so long as the distance between
them stayed constant. That is considerably harder and LAMMPS
does not do it. A stiff bond does not enforce the constraint,
just a soft constraint close to what you want. And you cannot
do it (in parallel) if the atoms are too far apart since no
processor will know about both atoms so it can compute the bond.
Steve