\begin{table}%t1[!htbp]
\caption{The configurations used to calculate the 
energy levels and the radiative data.
% The configurations are ordered according to their 
%relative energies  and grouped by odd or even parity.}
\label{tab:conf}}
%\centering
\par
%\scriptsize
%\footnotesize
%\tiny
%\normalsize
\begin{tabular}[c]{llll}
\hline\hline\noalign{\smallskip}
c1: 2s$^2$ & c2: 2s 2p & c3: 2p$^2$ & c4: 2s 3s   \\
c5: 2s 3p & c6: 2s 3d & c7: 2p 3s & c8: 2p 3p   \\
c9: 2p 3d & c10: 2s 4s & c11: 2s 4p & c12: 2s 4d   \\
c13: 2s 4f & c14: 2p 4s & c15: 2p 4p & c16: 2p 4d   \\
c17: 2p 4f & c18: 3s$^2$ & c19: 3s 3p & c20: 3s 3d   \\
c21: 3p$^2$ & c22: 3p 3d & c23: 3d$^2$ & c24: 3s 4s   \\
c25: 3s 4p & c26: 3s 4d & c27: 3p 4s & c28: 3s 4f   \\
c29: 3p 4p & c30: 3d 4s & c31: 3p 4d & c32: 3p 4f   \\
c33: 3d 4p & c34: 3d 4d & c35: 3d 4f & c36: 4s$^2$   \\
c37: 4s 4p & c38: 4s 4d & c39: 4p$^2$ & c40: 4s 4f   \\
c41: 4p 4d & c42: 4p 4f & c43: 4d$^2$ & c44: 4d 4f   \\
c45: 4f$^2$ &  &  &    \\
\hline
\end{tabular}
\normalsize
\end{table}