While in the Builder use the Forcefield/Select command. This command is activated on the left side by clicking on the FF button. Under Parameters in the box to right change the FF_Directory to user (yellow diamond should light up). Underneath Forcefield in the menu type in the path to cvff_ion.frc. If cvff_ion.frc is in the same directory as your input files you may still want to type /tmp/[your subdirectory]/cvff_ion.frc here for the path.

Then select Forcefield/Potentials and make sure that all of the settings are on Fix.

Potential Action [Fix]

Partial Charge Action [Fix]

Formal Charge Action [Fix]

Change the charge on the Mg atom. To do this using the Atom/Charge command in the Builder. Click on partial charge and then set the charge to 2.00 after you have highlighted the selection menu click on the Mg atom on the screen.

Use the Forcefield/Select command. This command is activated on the left side by clicking on the FF button. Under Parameters in the box to right change the FF_Directory to user (yellow diamond should light up). Underneath Forcefield in the menu type in the path to cvff_ion.frc. If cvff_ion.frc is in the same directory as your input files you may still want to type /tmp/[your subdirectory]/cvff_ion.frc here for the path.

Then select Forcefield/Potentials and make sure that all of the settings are on Accept.

Potential Action [Accept]

Partial Charge Action [Accept]

Formal Charge Action [Accept]

Once you have successfully assigned parameters to the Mg atom and water molecules you may save the assembly at this point using the Molecule/Put command. Recall that just because you can save the car and mdf files does not mean that they are complete. They should be checked.

If you wish to retrieve the saved file you must use the Molecule/Get command.

You must check your car and mdf files to see that the Mg atom type has been correctly installed. If it has not been type Mg in the column where the atom types are found. For example, the atom type for an oxygen in water is o* and for hydrogen in water h*. Type Mg in this column. Use the vi editor to edit the files.