 Our WWW server was re-configured while I was gone for a couple weeks, so
that broke some scripts ... sorry for the delays.

Steve

Dear list:

I'm trying to run a simulation of a single polystyrene chain. What I
found is:
(1) If the bond angle is set to 180 deg, and harmonic angle potential is
used, at low temperature it formed a rod-like structure, while at high
temperature a globular structure is formed;
(2) If the bond angle is set to less than 180 deg, say 108, generally a
globular structure can be formed.

I wonder between these two cases, which one is physical?
Thanks for any help.

jiwu

I would use a cosine style angle potential if you want the
equilibrium angle to be 180. As far as physicality, it
seems reasonable that the state you observe would
be depend on temperature, especially since the bonds
will be essentially straightened at low T.

Steve

If it is more reasonable to observe a temperature-dependent behavior,
would it be necessary to take into account torsional force while bond angle
is less than 180 deg? Because in this case polymer chain has additional
rotational entropy so that its structure is less rigid even in very low
temperature. A torsion can help it to form a more solid structure.
So, there seems to be two options:
1. angle=180 with bond potential and angle potential.
2. angle<180 with bond potential , angle potential and dihedral potential
Can I use either of them to simulate polymers?
Thank you.

jiwu