Magnetic and optical properties of exact PPP states of naphthalene

Abstract

The Pariser-Parr-Pople (PPP) hamiltonian for naphthalene is solve exactly, to all orders in configuration interaction, using diagrammatic (VB) theory. Standard molecular parameters place the ³B_2u, ¹B_2u, and ¹B_2a excitations within 0.3 eV of experiment. VB methods for correlated states are extended to the fine-structure constants D and E of the triplet state, which are found to be better than 0.01 cm^-1 without any adjustable parameters. Negative spin densities are found at the 9.10 carbons. The weak (f=0.0005) oscillator strength of the ¹B_2u transition is related to the absence of electron-hole symmetry on introducing different ionization potential at the 9.10 carbons. The static spin-correlation functions needed for D and E extend the accessible matrix elements over correlated states based on linear combinations of VB diagrams for model hamiltonians with one valence state per site.