4.10 TIPOMO - orbital selection

The package provides the program (TIPOMO) to select the $\pi$/$\sigma$ orbitals to be used for the calculation of the contributions to the various kind of density functions discussed before. The current version of the program works well in case of molecules containing second-row atoms and hydrogen atoms. Future releases will fix eventual limitations. When the program is run without argument, a fully conjugated $\pi$-system is assumed. Alternatively, one can issue the number of double bonds as an argument, i.e., TIPOMO $n_{\pi }$. The search of $\pi$-orbitals goes as described in the following.

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  Count how many Hydrogen atoms are in the molecules ($n_{\text{H}}$).

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  Calculate the number of core orbitals $n_{\text{core}}=\text{NATO}-n_{\text{H}}$, where NATO is the total number of atoms.

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  When run without argument, set $n_{\pi }=n_{\text{core}}/2$, which is the correct value in case of fully conjugated $\pi$-systems.

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  For each occupied molecular orbitals, calculate the maximum value of the electron density on the nuclei and sorts these densities by descending order. The first $n_{\text{core}}$ molecular orbitals in the ordered list are designed to be core orbitals.

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  For each of the remaining orbitals, calculate the maximum value of the electron density for each pair of bonded atoms in the bond center position and sorts these densities by ascending order. The first $n_{\pi }$ are designed to be $\pi$-orbitals.

The program can be used in four different ways:

TIPOMO    : write PIG file with pi-orbital indices
TIPOMO -  : write SIG file with sigma-orbital indices
TIPOMO  n : write PIG file with n indices
TIPOMO -n : write SIG file with n indices

Both PIG and SIG files can be used by the IC programs by means of the -qf option. Note that these files contain $n+1$ lines, the first with the value of $n$ and the others with the molecular orbital indices (one per line) designed to be $\pi$ or $\sigma$ orbitals.