In NEGF calculations, the C direction is always considered the transport direction, and transmission can only be calculated when the A and B directions are orthogonal to C in the unit cell. However, for a monoclinic structure, no matter how I cleave it, the A and B directions are never orthogonal to C.
My current approach is to cleave the surface first, add vacuum along the C direction (above and below the surface), perform structure optimization only on the surface layers, and then switch the B and C directions for the transmission calculation.
However, even after doing this, the C (formerly B) direction is still not orthogonal to the other axes.
How can I solve this issue?
