arXiv subjects

R. Podeszwa

Publications and source records attributed to R. Podeszwa.

2 recordsLinked to original sources

arXiv2002

Electronic correlation in cyclic polyenes. Behavior of approximate coupled-pair theories for large rings

We investigate the cyclic polyenes (annulenes) C_{M}H_{M}, described by the Pariser--Parr--Pople (PPP) model, by means of the approximate coupled-pair theories (ACP, ACPQ). For the systems with the spectroscopic value of the PPP resonance integral beta=2.5 eV, the ACP method breaks down for M >= 446, and the ACPQ method--for M>194. In the ACPQ method, for M>170, two close lying solutions have been observed that become quasi-degenerate for M >= 198. The results indicate that the ACP and ACPQ methods cannot be applied to the one-dimensional metallic case.

physics.chem-ph↗

arXiv2002

Multiple solutions of coupled-cluster equations for PPP model of [10]annulene

Multiple (real) solutions of the CC equations (corresponding to the CCD, ACP and ACPQ methods) are studied for the PPP model of [10]annulene, C_{10}H_{10}. The long-range electrostatic interactions are represented either by the Mataga--Nishimoto potential, or Pople's R^{-1} potential. The multiple solutions are obtained in a quasi-random manner, by generating a pool of starting amplitudes and applying a standard CC iterative procedure combined with Pulay's DIIS method. Several unexpected features of these solutions are uncovered, including the switching between two CCD solutions when moving between the weakly and strongly correlated regime of the PPP model with Pople's potential.

physics.chem-ph↗