\cdot
\\
\phi _{m_{N}k_{N}}(\vec{r}_{1}) & \phi _{m_{2}k_{2}}(\vec{r}_{2}) & \cdot
\cdot \cdot & \phi _{m_{N}k_{N}}(\vec{r}_{N})
\end{array}
\right| $         (3)

with a given total orbital angular momentum $L=\sum_{i}(m_{i}-k_{i})$ are composed.

    From the BFs, the eigenstates of the dot are expanded as

                          $\Psi =\sum C_{\alpha
}\psi _{\alpha }$                                                                     (4)

     where  the coefficients $C_{\alpha }$ can be obtained via a procedure of diagonalization.  The $\ \psi _{\alpha }$ are arranged in such a sequence that $<\psi _{\alpha }|H|\psi _{\alpha }>$ $\leq $ $<\psi
_{\alpha +1}|H|$ $\psi _{\alpha +1}>$ . Evidently, in such a sequence, the $\ \psi _{\alpha }$ with a smaller $\alpha $ is more important to the low-lying states, while those with a very large $\alpha $ can be neglected.  The $H$ will be diagonalized step by step. In the first step, $H$ is diagonalized in a smaller space with N$_{a}$ BFs ( $\psi _{1}$ to $\psi
_{N_{a}}$) . Then, $H$ is diagonalized again in a larger space with N$_{b}$ BFs ( from $\psi _{1}$ to $\psi _{N_{b}}$ , and N$_{b}$ is considerably larger than N$_{a}$) . This process repeats again and again until a satisfactory convergency of the lower eigenenergies is achieved.  In the first step, all the $\ \psi _{\alpha 