Rigid Molecule Simulation (not specified angle, dihedral in PSF file)

[YounesN]

Describe the bug If the user doesn't specify the dihedral or angle the GOMC cannot build the molecule and will crash

To Reproduce Run any simulation and removed dihedral or angle

Expected behavior To run normally

We should double check if the user has specified these requirements. If not we have give a warning/error or set a value by default. @msoroush do you want to set 0 by default or throw an error?

[msoroush]

For future release we need to implement the support for rigid molecule simulation. More information about what rigid molecule GOMC can simulate and how to set up the system, can be found here.

In summary: GOMC can simulate rigid molecules in all ensembles for the following molecular topology:

1. Linear and branched molecules with no dihedrals. For instance, carbon dioxide, dimethyl ether, and all water models (SPC, SPC/E, TIP3P, TIP4P, etc).

2. Cyclic molecules, where at least two atoms in all defined angles, belong to the body of the ring. For instance, benzene, toluene, Xylene, and more.

.. important::

1.  For linear and branched molecule, the molecule's bonds and angles  will be adjusted according to the equilibrium values, defined in parameter file.

2.  For cyclic molecules, the molecule's bonds and angles would not change! It is very important to create the initial molecule with correct bonds and angles.