BONDS — Print only non-zero elements of final two-center bond order matrix.
The bond order between pairs of atoms is calculated and printed. In this context a bond is defined as the sum of the squares of the density matrix elements connecting any two atoms. For ethane, ethylene, and acetylene the carbon-carbon bond orders are roughly 1.00, 2.00, and 3.00 respectively. The diagonal terms are the valences calculated from the atomic terms only and are defined as the sum of the bonds the atom makes with other atoms. This type of analysis is carried out by the Coulson method (see Chapter 17, References for references). In UHF wavefunctions (alpha and beta density matrices) the calculated valence will be somewhat incorrect. Only non-zero bond order values will be printed, which makes the output easier to read and for larger molecules this significantly reduces the size of the output.
This option is the same as ESP except that it prints the bond order for all atom pairs in a simple matrix format. This keyword should be used if the output is to be read by another program that expects the bond information in the older AMPAC format.
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