About automating consolidation of parameters while using GMSO ForceField XML.

[umesh-timalsina]

Since GMSO forcefields are generic with expressions or parameters, it might be nice to figure out a way to include this information while dealing with them. For example, take for example a periodic torsion, with the current version of the XML schema, we have to use a section like this for the whole representation.

   <DihedralType name="DihedralType_Periodic_Proper_CH3_CH_O_H" class1="CH3" class2="CH" class3="O" class4="H">
      <Parameters>
        <Parameter name="k0" value="0.0"/>
        <Parameter name="k1" value="0.416955197548017"/>
        <Parameter name="phi_eq1" value="0.0"/>
        <Parameter name="k2" value="-0.0579667482245528"/>
        <Parameter name="phi_eq2" value="180"/>
        <Parameter name="k3" value="0.37345529632637"/>
        <Parameter name="phi_eq3" value="0.0"/>
        <Parameter name="k4" value="0.0"/>
        <Parameter name="phi_eq4" value="0.0"/>
        <Parameter name="k5" value="0.0"/>
        <Parameter name="phi_eq5" value="0.0"/>
      </Parameters>
    </DihedralType>

This is great and all, but it might be difficult to cumbersome all these all the long-form equations like these:

k0 + k1 * (1 + cos(1 * phi - phi_eq1)) + k2 * (1 + cos(2 * phi - phi_eq2)) + k3 * (1 + cos(3 * phi - phi_eq3)) + k4 * (1 + cos(4 * phi - phi_eq4)) + k5 * (1 + cos(5 * phi - phi_eq5))

It might make sense to allow the writing of consolidated parameters as a list, where a parameter will have a name and value associated with it. Alternatively, one can also consider consolidating parameters based on alpha-numeric selection, which will inevitably lead to edge cases as well as potential bugs. For example, the above periodic dihedral can also be written as:

 <DihedralType name="DihedralType_Periodic_Proper_CH3_CH_O_H" class1="CH3" class2="CH" class3="O" class4="H">
      <Parameters>
        <Parameter name="k0" value="[0.0, 0.416955197548017, -0.0579667482245528, 0, 0]"/>
	 <Parameter name=”phi_eq”, value=”[0.0, 0.0, 0.0, 0.0, 0.0, 0.0]”/>
      </Parameters>
    </DihedralType>

So, this can be achieved by relaxing the schema definition for parameters to optionally include a list of floats. However, the minutia of the validation code (length) should be left up to the user.