A Density Matrix Renormalization Group Method Study of Optical Properties of Porphines and Metalloporphines

TL;DR

This study employs the symmetrized DMRG method with the PPP model to analyze the optical properties of porphines and metalloporphines, revealing detailed electronic structures and optical responses consistent with experimental data.

Contribution

It introduces a combined DMRG and PPP model approach to accurately compute optical properties and charge densities of porphines and metalloporphines, including effects of metal ions.

Findings

Charge density rearrangement upon excitation.

Porphine has an 18-annulenic ground state structure.

Metalloporphines show increased charge on metal ions and degenerate excited states.

Abstract

The symmetrized Density-Matrix-Renormalization-Group (DMRG) method is used to study linear and nonlinear optical properties of Free base porphine and metallo-porphine. Long-range interacting model, namely, Pariser-Parr-Pople (PPP) model is employed to capture the quantum many body effect in these systems. The non-linear optical coefficients are computed within correction vector method. The computed singlet and triplet low-lying excited state energies and their charge densities are in excellent agreement with experimental as well as many other theoretical results. The rearrangement of the charge density at carbon and nitrogen sites, on excitation, is discussed. From our bond order calculation, we conclude that porphine is well described by the 18-annulenic structure in the ground state and the molecule expands upon excitation. We have modelled the regular metalloporphine by taking an effective electric field due to the metal ion and computed the excitation spectrum. Metalloporphines have $D_{4h}$ symmetry and hence have more degenerate excited states. The ground state of Metalloporphines show 20-annulenic structure, as the charge on the metal ion increases. The linear polarizability seems to increase with the charge initially and then saturates. The same trend is observed in third order polarizability coefficients.