I am trying to simulate an infinite 2D triangular lattice in Comsol for phononic band structure but I am confused that how should I use periodic floquet boundary conditions on the unit-cell.
A unit cell that I am using is given below.
It has 6 sides, L1,L2,...,L6. In the case of a square lattice, we simply just select floquet boundary conditions on both pairs of opposite sides because k_x and k_y are parallel to those sides.
Now, the pair of opposite sides (i.e. L1 and L4, L2 and L5, and L3 and L6) are not parallel to the k vectors. How do we define boundary conditions now?
(I am trying to calculate the band structure on \Gamma, K and M points which are defined on this orthogonal k_x, k_y axis.)
Is there any other way to define k axis and simualte triangular lattice?