I have a large matrix for a 1D zigzag edge model of an otherwise $3\times 3$ tight-binding Hamiltonian (3 basis functions, each corresponding to an atomic orbital), involving the variable $k_x$. The large matrix contains blocks of this $3\times 3$ Hamiltonian for each unit cell involved (I chose ...

Rephrasing the above, what is the pattern in which the electron-density data is stored in the CHGCAR file? I understand that the electron density data in a CHGCAR file is in the form of a 3D Fortran array, but I believe that such electron density data should be stored in 3 columns (NX,NY,NZ). Ins...