armchair width is odd

[sam1026]

please tell me why the width of the armchair GNR is odd and zigzag GNR is even?

[zh]

I guess that no one can understand what is the meaning of "odd" and "even" in your question.

The width of GNR can be roughly estimated by the C-C bond length of graphene sheet, e.g., armchair:   x *sqrt(3)* d_{C-C}; zigzag:  x* 3* d_{C-C}, where the value of "x" roughly depends on the number of hexagonal rings perpendicular to the edge direction.

[sam1026]

Dear Professor, sorry i was unable to mention the type of problem. Actually, this is the GFET snapshot in VNL, when i select the width to be odd for ZAZ it says not possible but when the width of the AZA is selected even it says same error. thankyou

[Umberto Martinez]

Actually it says "Width must be an even number" when you select ZAZ
and "Width must be an odd number" when you select AZA

this is the width of the ribbons belonging to the electrodes.
You have this constrain in order to match properly the different Z and A parts of the device.

[sam1026]

Thankyou firstly  so,does it mean actually the electrodes ( left and right )only.

should it not be is this not necessary for the i.e. the central electrode too?

i will really appreciate if you can tell me the reason too 

thanks   

[Umberto Martinez]

Follow the new version of the initial part of the Graphene Device tutorial http://quantumwise.com/documents/tutorials/latest/GrapheneDevice/index.html/chap.buildingdevice.html

and everything will be clear

As stated there,
"Note that the width of the two electrodes is dictated by the width of the central region created before."

[sam1026]

thanks