  It is generally believed that the inhomogeneous
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase appears in a color superconductor
when the pairing between different quark flavors is under the circumstances of
mismatched Fermi surfaces. However, the real crystal structure of the LOFF
phase is still unclear because an exact treatment of 3D crystal structures is
rather difficult. In this work we present a solid-state-like calculation of the
ground-state energy of the body-centered cubic (BCC) structure for two-flavor
pairing by diagonalizing the Hamiltonian matrix in the Bloch space without
assuming a small amplitude of the order parameter. We develop a computational
scheme to overcome the difficulties in diagonalizing huge matrices. Our results
show that the BCC structure is energetically more favorable than the 1D
modulation in a narrow window around the conventional LOFF-normal phase
transition point, which indicates the significance of the higher-order terms in
the Ginzburg-Landau approach.
