Impementing a different type of dihedral equation

Hi Perci,

It looks like that dihedral potential has the same functional form as the CHARMM dihedral, so you should be able to model it just fine in Cassandra v1.2 by listing multiple CHARMM dihedrals for the same 4 atoms. Please note, you will need to add the extra dihedrals into the *.mcf directly since mcfgen.py does not support multiple dihedrals.

If you need further help, please upload the *.mcf you have constructed for your molecules.

Ryan

Hi Perci,

To implement a new dihedral functional form, please do the following:

1) energy_routines.f90, subroutine Compute_Molecule_Dihedral_Energy: This function evaluates the energy for a given dihedral. There is an IF statement that handles the available functional forms. You can add a new functional form by following the templates of the existing forms.

2) input_routines.f90, subroutine Get_Dihedral_Info: This function parses and stores the functional form type and parameters located in the input files. You add the new form here so it is read from the input files.

I think that's it. You will also need to declare the relevant variables in global_variables.f90 (i.e. lines 244-249). Before running a calculation for research, I'd recommend testing your implementation with a simple system (i.e. ideal gas butane) and compute the energy for various dihedral angles. Then check if you get the energies that you'd expect.