\begin{table}%t1
\caption{\label{table:optimise}Orbital optimisations.} 
%\centerline
 {
\begin{tabular}{clc}
\hline\hline\\[-5pt] 
\multicolumn{1}{c}{Orbital}&\multicolumn{1}{l}{Optimised on energy of}
&\multicolumn{1}{c}{Configurations used}\\[5pt]
\cline{1-3}\\[-5pt]
1s &\multicolumn{2}{l}{HF* orbital for \ion{Mg}{v}} \\[3pt] 
2s, 2p & HF* orbitals re-optimised &  \\
       & on 2s2p$^5~^1$P$^{\rm o}$ & 2s2p$^5$\\[3pt]                  
3s & 2s$^2$2p$^3$($^2$D$^{\rm o}$)3s~$^1$D$^{\rm o}$ & 2s$^2$2p$^3$3s \\[3pt]
3p & 2s$^2$2p$^3$($^2$D$^{\rm o}$,$^2$P$^{\rm o}$)3p~$^3$D & 2s$^2$2p$^3$3p \\[3pt]
$\overline{\rm 4s}$ & 2s$^2$2p$^3$($^2$D$^{\rm o})$3s~$^1$D$^{\rm o}$ & 2s$^2$2p$^3$3s,\\ && 2s2p$^3$3s$^2$, 2s2p$^3$3s$\overline{\rm 4s}$,\\ && 2p$^3$3s$^2\overline{\rm 4s}$, 2p$^3$3s$\overline{\rm 4s}^2$\\[3pt] 
$\overline{\rm 4p}$ & 2s$^2$2p$^3$3s~$^5$S$^{\rm o}$ & 2s$^2$2p$^3$3s,\\&& 2s$^2$2p$^2$3s3p, 2s$^2$2p$^2$3s$\overline{\rm 4p}$ \\[3pt]
$\overline{\rm 3d}$ & 2s2p$^5~^1$P$^{\rm o}$ & 2s2p$^5$\\&& 2s$^2$2p$^3$3s, 2s$^2$2p$^3\overline{\rm 3d}$ \\[3pt] 
\hline\\[-3pt]
\end{tabular}}
\par
\smallskip
*HF -- Hatree-Fock orbitals of \cite{clementi}.
\end{table}