N-Block Separable Random Phase Approximation: Application to metal clusters and C60 fullerene

TL;DR

This paper introduces an N-block separable RPA model that simplifies calculations of collective excitations in metal clusters and C60, accurately matching experimental and full RPA results.

Contribution

It generalizes the separable RPA approach to handle multiple collective excitations and reduces computational complexity.

Findings

Accurately describes collective excitations in sodium clusters and C60

Reduces numerical effort compared to full RPA

Achieves good agreement with experimental data

Abstract

Starting from the Random Phase Approximation (RPA), we generalize the schematic model of separable interaction defning subspaces of ph excitations with different coupling constants between them. This ansatz simplifies the RPA eigenvalue problem to a finite, small dimensional system of equations which reduces the numerical effort. Associated dispersion relation and the normalization condition are derived for the new defined unknowns of the system. In contrast with the standard separable approach, the present formalism is able to describe more than one collective excitation even in the degenerate limit. The theoretical framework is applied to neutral and singly charged spherical sodium clusters and C60 fullerene with results in good agreement with full RPA calculations and experimental data.