dihedral distribution no symmetrical

I don't see anything wrong with your parameters. If you have adequate
sampling, you should be getting a symmetric distribution of dihedral
angles.

However the fact that your data at 500K is much more symmetric than
your data at 300K suggests to me that perhaps you do have a sampling
problem. Is this possible? Do you have any long polymers in your
system? Have you visualized your trajectory? Are the polymers
tangled up and "stuck" (trapped)?
This is just a guess. (I frequently see these kinds of polymers in my work.)
Cheers!

Andrew

the dihedral section in my data file:

  1 8.3667 0.0000 1.1932 0.0000 0.0000 0.0000
  2 0.0000 0.0000 3.9661 0.0000 0.0000 0.0000
  3 0.0000 0.0000 4.8498 0.0000 0.0000 0.0000
  4 0.0000 0.0000 1.7234 0.0000 0.0000 0.0000
  5 0.0000 0.0000 1.5000 0.0000 0.0000 0.0000
  6 0.0000 0.0000 1.8769 0.0000 0.0000 0.0000
  7 0.0000 0.0000 4.4072 0.0000 0.0000 0.0000
  8 0.0000 0.0000 1.5590 0.0000 0.0000 0.0000
  9 -0.2802 0.0000 -0.0678 0.0000 -0.0122 0.0000
10 -0.2802 0.0000 -0.0678 0.0000 -0.0122 0.0000
11 -0.0228 0.0000 0.0280 0.0000 -0.1863 0.0000
12 0.0000 0.0000 0.0316 0.0000 -0.1681 0.0000
13 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
14 0.9513 0.0000 0.1155 0.0000 0.0720 0.0000
15 0.0000 0.0000 4.4072 0.0000 0.0000 0.0000
16 0.0000 0.0000 1.5590 0.0000 0.0000 0.0000
17 -0.2801 0.0000 -0.0678 0.0000 -0.0122 0.0000
18 -0.2802 0.0000 -0.0678 0.0000 -0.0122 0.0000
19 -0.1435 0.0000 0.2530 0.0000 -0.0905 0.0000
20 0.7137 0.0000 0.2660 0.0000 -0.2545 0.0000
21 -0.1820 0.0000 -0.1084 0.0000 -0.7047 0.0000
22 -0.1432 0.0000 0.0617 0.0000 -0.1083 0.0000
23 0.0000 0.0000 0.0316 0.0000 -0.1681 0.0000
24 -0.1435 0.0000 0.2530 0.0000 -0.0905 0.0000
25 -0.6732 0.0000 -0.4778 0.0000 -0.1670 0.0000
26 0.1863 0.0000 -0.4338 0.0000 -0.2121 0.0000
27 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
28 0.0000 0.0000 4.8498 0.0000 0.0000 0.0000
29 0.0000 0.0000 1.7234 0.0000 0.0000 0.0000
30 -0.6900 0.0000 0.5097 0.0000 0.0095 0.0000
31 0.7137 0.0000 0.2660 0.0000 -0.2545 0.0000
32 0.0000 0.0000 0.0316 0.0000 -0.1681 0.0000
33 0.0000 0.0000 0.0316 0.0000 -0.1681 0.0000
34 -0.1432 0.0000 0.0617 0.0000 -0.1083 0.0000
35 -0.1435 0.0000 0.2530 0.0000 -0.0905 0.0000
36 -0.6732 0.0000 -0.4778 0.0000 -0.1670 0.0000

Alas, I am not familiar with the FRC file format.
In LAMMPS 0 degrees corresponds to the "cis" conformation.
(terminology:
Cis–trans isomerism - Wikipedia
LAMMPS Molecular Dynamics Simulator)

Please excuse me for posting those links.
:slight_smile:
(Sorry, I'm not a chemist.)