calcaultions using same nc file

[esp]

I ran transmission calcs and got a Ids vs Vgs curve like attached
tfet1.gif

I ran similar curves at different Vds, 0.4, 0.5, 0.6 ... all using same nc file, and always saving to same nc when done .. then i went back to the 0.5V vds versiob

Now I am seeing something very strange ... i ran a Vds sweep at a fixed Vgs, as attached:
tfet2.gif

Now I realized I did not take the minimum current point into consideration and I used Vgs = 0.5, which is not what I wanted to do .. so i ran again with Vgs = 0.25 ... but now the results look very odd .. and I am wondering if it has something to do with me using the same nc file every time i calculate ... ?  can the calculations get messed up if starting from the same nc file under many different biases? looks wierd
tfet3.gif

[esp]

i could of course run a fresh calculation, but it takes so long i wanted to start from the same one

[Anders Blom]

Honestly, I have no idea - it's not possible to tell from the plots if you have done it right or wrong. In fact, I can't even tell what numbers are what, the scales are different and the points too, and plot 3 has no labels on the axes. Sorry.

[esp]

well the only plot with no axes is plot 3 ... plot 3 is the same as 2 (Ids versus Vds) except it is at Vgs=0.25 instead of Vgs=0.5 ...

My question though does not depend on the plots .. I am asking whether I can use the same nc file with the initial calc completed, to compute transmission for many different biases, different Vds, different Vgs ... for example for the vds sweep, i save the object ids as biasSweep1, 2, 3, 4, 5 .... then i use a different Vds and/or Vgs... and save over it .. the question is, will the nc file or the initial calc (which I am reading in , using update() and saving again) get messed up by doing this?

[esp]

I suppose i can just run a fresh calculation and get my answer .. thank you

[Anders Blom]

It depends a bit on how you use object IDs. If you write an object to the file with the same object ID as an existing one, it will be overwritten, otherwise appended to the file. There is no risk of destroying anything unless you make a mistake in the IDs.

[esp]

ok that is all I wanted to know .. even so, i dont understand why the Id vs Vds curve is so different at Vgs=0.25 than it is at Vgs=0.5, so I am just going to run everything again for piece of mind  .. thank you

[Anders Blom]

Congratulations on hitting 300 posts I still lead though

[esp]

haha .. well this forum is invaluable . at least for some like me who has not used this type of simulator before ... you and the others at Quantumwise are indeed very wise to realize that this support can bring this tool to a much larger audience ... I am not a semiconductor person at all, i am interested more in circuit level and architecture level concepts, but we found we needed some solid cutting edge device simulations as a baseline, in order to do some higher level studies .. I surveyed all the tools available and i chose ATK based of course on the fact that it uses a very robust and complete set of algorithms, but also that it had the python interface . i work almost exclusively in python ... i use the GUI only to make sure the structures i make in python make sense ... anyway ... this forum is very useful and without your help I would not have gotten very far i think ...