I need to calculate the "charge" in the channel to try to estimate capacitance for a GNR device ... from some relevant papers, i see the technique many use use is to calculate a small change in charge with respect to gate voltage (for Cgate for example) .. Q = CV, C = dQ/dV ... now, the idea i found in another post was to use the ElecronDensity, then add it up for example over the entire channel to get charge .. I was planning on calculating Q1 at V1, then Q2 and V2, then C = (Q2-Q1)/(V2-V1) .... does this all sound reasonable?

Now, I have been running ElectronDensity all week .. I cannot get it to converge .. my current job is 36 hours running, still on the base calculation .. no points completed yet ... it is taking forever ... i even reduced the k points a bit and the energy range ... it never got to the Elec.Dens. calc yet ... [Update: As Dr. Blom noted, it is the base calculation taking a long time to converge, not the E.D. calculation]

So, I am wondering, I believe i tried before and electron difference density was faster ... is this expected? if so, then wouldn't the method above of calculating difference in charge at two gate voltages give the same answer? In other words if i am interested in the difference at two different gate voltages and not the absolute value of charge or elec dens, then wouldnt both methods give the same answer, if i used either ElectronDensity, or ElectronDifferenceDensity?