Dear All

I like to make a graphene bilayer. I wanted to use "honeycomb" definition in the lattice library but I found something strange! The strange thing is the definition of vertexes:

<UNITCELL name="honeycomb" dimension="2"> <VERTEX><COORDINATE>0 0</COORDINATE></VERTEX> <VERTEX><COORDINATE>-0.288665771484375 0.5773468017578125</COORDINATE></VERTEX> ....... ......

</UNITCELL>

I don't know how these two numbers "-0.288665771484375 0.5773468017578125" were generated ( they are near to "-1/(2*sqrt(3)), 1/sqrt(3)" !) I think if we suppose the vertex coordinate is defined according to the lattice vectors (.i.e. a1=[1 0], a2=[1/2 sqrt(3)/2]), then the correct numbers should be: "-1/3, 2/3" (-1/3*a1+2/3*a2). So the correct "UNITCELL" should be:

<UNITCELL name="honeycomb" dimension="2"> <VERTEX><COORDINATE>0 0</COORDINATE></VERTEX> <VERTEX><COORDINATE>-1/3 2/3</COORDINATE></VERTEX> ....... ......

</UNITCELL>

I checked the new "UNITCELL", and I found the lattice is more like to graphene. If I am wrong please correct me.

Thanks

Kaveh Edalat