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Il Nuovo Cimento (1955-1965)

, Volume 17, Issue 5, pp 644–664 | Cite as

On the non-orthogonality problem in the semi-empirical MO-LCAO method

  • G. Del Re
Article

Summary

An explicit correlation between semi-empirical MO-LCAO calculations forπ-systems including and not including overlap is derived and discussed under the assumption that overlap integrals, when taken into account, are proportional to the corresponding bond integrals. It is shown that, so far as atomic charges are concerned, the introduction of overlap makes practically no difference in the results. On the contrary all other quantities undergo sometimes serious changes. This is shown by means of a few numerical examples; it gives some support to the idea that the practice of neglecting overlap may not be so sound as has been believed.

Riassunto

Il metodo semi-empirico MO-LCAO viene di solito applicato ai sistemiπ trascurando gli integrali di ricoprimento. Nel presente lavoro vengono posti in diretta, esplicita correlazione calcoli in cui si trascurano tali integrali e calcoli in cui essi vengono introdotti sotto la condizione restrittiva che siano proporzionali agli integrali di legame. Diviene cosí possibile discutere in modo particolareggiato l’effetto dell’introduzione degli integrali di ricoprimento. Per quanto concerne le cariche atomiche, l’introduzione del ricoprimento non produce alcun cambiamento. Tutte le altre quantità vengono invece profondamente modificate, come mostrano sia le formule generali che alcuni esempi numerici. Contrariamente a quanto si è creduto, il trascurare gli integrali di ricoprimento non è lecito in generale, e può influire anche sulla validità quantitativa dei risultati dei calcoli MO-LCAO.

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Copyright information

© Società Italiana di Fisica 1960

Authors and Affiliations

  • G. Del Re
    • 1
  1. 1.Quantum Chemistry GroupUniversity of UppsalaUppsala

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