Double Time Window Targeting Technique: Real time DMRG dynamics in the PPP model

TL;DR

This paper introduces the double time window targeting (DTWT) technique, an efficient adaptive DMRG method for real-time dynamics in the PPP model, revealing faster charge and spin propagation due to long-range correlations in conjugated polymers.

Contribution

The paper develops the DTWT method combining pace keeping and time-step targeting algorithms, enabling accurate real-time DMRG simulations of the PPP model with long-range interactions.

Findings

Charge propagates faster than spin in the PPP model.

Long-range correlations increase electron propagation speeds.

Simple Hubbard model renormalization cannot capture PPP dynamics.

Abstract

We present a generalized adaptive time-dependent density matrix renormalization group (DMRG) scheme, called the {\it double time window targeting} (DTWT) technique, which gives accurate results with nominal computational resources, within reasonable computational time. This procedure originates from the amalgamation of the features of pace keeping DMRG algorithm, first proposed by Luo {\it et. al}, [Phys.Rev. Lett. {\bf 91}, 049701 (2003)], and the time-step targeting (TST) algorithm by Feiguin and White [Phys. Rev. B {\bf 72}, 020404 (2005)]. Using the DTWT technique, we study the phenomena of spin-charge separation in conjugated polymers (materials for molecular electronics and spintronics), which have long-range electron-electron interactions and belong to the class of strongly correlated low-dimensional many-body systems. The issue of real time dynamics within the Pariser-Parr-Pople (PPP) model which includes long-range electron correlations has not been addressed in the literature so far. The present study on PPP chains has revealed that, (i) long-range electron correlations enable both the charge and spin degree of freedom of the electron, to propagate faster in the PPP model compared to Hubbard model, (ii) for standard parameters of the PPP model as applied to conjugated polymers, the charge velocity is almost twice that of the spin velocity and, (iii) the simplistic interpretation of long-range correlations by merely renormalizing the {\it U} value of the Hubbard model fails to explain the dynamics of doped holes/electrons in the PPP model.