Effect of semi-empirical parameters on the simple random-phase approximation calculations of conjugated hydrocarbons

✍ Scribed by B. Guha Niyogi; D. C. Mukherjee; A. B. Sannigrahi

• Publisher: John Wiley and Sons
• Year: 1977
• Tongue: English
• Weight: 662 KB
• Volume: 12
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/qua.560120405

✦ Synopsis

Abstract

Singlet‐singlet transition energies, oscillator strengths, triplet energy levels, and the ground state correlation energy of a number of conjugated hydrocarbons have been calculated by the simple random‐phase approximation (RPA) within the framework of the Pariser‐Parr‐Pople (PPP) model. The effect of semi‐empirical parameters in such calculations has been examined in detail. A set of parameters has been deduced from these parametric studies which is found to yield results for the singlet spectra of the molecules in excellent agreement with experiment. It is, however, not possible to treat the triplet states using these same parameters, since they produce triplet instabilities in all the molecules. The triplet instability problem associated with semi‐empirical RPA calculations has been discussed in detail.