  We present a new method to calculate Lyapunov exponents of rigid diatomic
molecules in three dimensions (12N dimensional phase space). The spectra of
Lyapunov exponents are obtained for 32 rigid diatomic molecules interacting
through the Weeks-Chandler-Anderson(WCA) potential for various bond length and
densities, and compared with those in Y.-H. Shin et al. [Phys. Rev. E 64,
041106 (2001)]. Our algorithm is easy to implement and total CPU time is
relatively inexpensive.
