Is there a way to describe the charge across the device as a function of voltage?

Suppose I were to write the current across an ideal capacitor having terminals t1 and t2 and capacitance c. The code might look something like this:

   I(t1,t2) <+ c*ddt(V(t1,t2));

I'm trying to come up with a code that will instead keep track of the charge across the device like this:

Q(t1, t2) <+ .... ;

Where Q would keep track of the charge across the terminals.

Thank you for any feedback.