Which fix command !!

Hi,

  I am trying to simulate a system consists of bonds as well as angles.
There are 2 types of atoms where the bond is between type1-type2 atoms
and the angles are between type1-type2-type1 triplets. where the initial
bond lengths are not same and my system demands also a different
equilibrium bond length and that would be my equilibrium configuration.

  So, I am specifying different R_o for them as well. My expectation
should be the system will relax to the local minima of its P.E spectrum
ehere the bond lenght would be just equal to R_o's. the constraints of
the system is, total no of atoms will be unaltered as well as there will
be no removal of bonds or addition of unwanted bonds take place.

  Here comes my confusion about the perfect fix command. I have tried NVE,
NVT, NPT . the outcomes are followed.

for each of the cases the equilibrium bond length is 80% of its initial
value.

1. For NVE, the system is expanding and the energy is not getting constatnt.
2. For NPT, though the system is compressing but the energy is not
getting minimized as well as the 'tstart' and 'tstop' is not arriving to
its defined value.
3. For NVT, the problem is same like NPT case.

Can you please mention which 'fix' will be physically meaningful and
suffice my purpose ?

Thanks,

best,

I seriously doubt that the choice of integration fix is the cause of your problems. It almost never is. More likely are errors in other parts of your input leading to incorrect dynamics. There is far too little information in you description for any kind of advice.

Axel

I seriously doubt that the choice of integration fix is the cause of your
problems. It almost never is. More likely are errors in other parts of
your input leading to incorrect dynamics. There is far too little
information in you description for any kind of advice.

There is no other dynamics running in my simulation. Only they are bonded
and angled. So, i am attaching my input script as well as read_data file.
Can you please take a look.

Thanks,
Saikat

data.random_network (1000 KB)

in.lammps (1.84 KB)

hi,

please consider how close your atoms are to each other (see the two histograms of distances attached). even though your box spans sth like from -10 to 15, your atoms seem to be distributed between 0 and 5. when you initiate your system make sure the particles don’t overlap, or choose the bond lengths and nonbonded interaction parameters properly.

best,

nikita

dists_close.png

dists_full.png