yes dear, you are right but i want to write a code for geometry of fcc and i wrote it but i don't know how can i apply periodic boundary condition on for cubic? i mean i must connect the topest point to lowest point of lattice i don't know how can i show this?
but i supposed that each site has 12 neighbours and if take an array like this for nearest neighbours :
(number of neighber ,number of site )
foe example: (3,4) shows the third neughbour of 4th spin,
and then try to fill it, i used this way :
if i show each point of fcc with n=i*a1 + j*a2 + k*a3 in which, a1 ,a2, a3 are translation vector , then i ,j ,z are integer numbers
then the cubic dimension is L*L*L and each site of lattice can be shown by :
n=i+j*L+k*L^2
and i can calculate the "n" of all of 12 neighbours of each site. but i don't know how use peridic condition in all of 3 direction of x,y,z?