Dear APBS users, 

i have been performing electrostatic calculations on a macromolecular complex using APBS with the aim to have an electrostatic binding energy profile along a reaction trajectory (MD frames)...

In order to do this and minimize accuracies I have chosen a focusing approach with grid dimensions of 161 A^3 (cubic grid) and glen variable across three calculations (an initial one (bcfl = zero) and two subsequent focusing calculations (bcfl = focus)) in which the glen was 200, 100 and 75^3 respectively. 

I was wondering how I could calculate, how much of the complex occupies the grid in the three different glen conditions. Is there an empirical relation that allows me to calculate how much (percentage will do) of the complex is actually occupying the grid? 

I would expect that decreasing glen such percentage would increase. 

Can you please advice me on this? 

Thank you very much in advance for any response.