  Structure of cold nuclear matter at subnuclear densities for the proton
fraction $x=0.5$, 0.3 and 0.1 is investigated by quantum molecular dynamics
(QMD) simulations. We demonstrate that the phases with slablike and rodlike
nuclei, etc. can be formed dynamically from hot uniform nuclear matter without
any assumptions on nuclear shape, and also systematically analyze the structure
of cold matter using two-point correlation functions and Minkowski functionals.
In our simulations, we also observe intermediate phases, which has complicated
nuclear shapes. It is found out that these phases can be characterized as those
with negative Euler characteristic. Our result implies the existence of these
kinds of phases in addition to the simple ``pasta'' phases in neutron star
crusts and supernova inner cores.
  In addition, we investigate the properties of the effective QMD interaction
used in the present work to examine the validity of our results. The resultant
energy per nucleon $\epsilon_{n}$ of the pure neutron matter, the proton
chemical $\mu_{p}^{(0)}$ in pure neutron matter and the nuclear surface tension
$E_{\rm surf}$ are generally reasonable in comparison with other nuclear
interactions.
