The prediction of spectral properties via linear response (LR) theory is an important tool in quantum chemistry for understanding photo-induced processes in molecular systems. With the advances of quantum computing, we recently adapted this method for near-term quantum hardware using a truncated active space approximation with orbital rotation, named quantum linear response (qLR). In an effort to reduce the classic cost of this hybrid approach, we here derive and implement a reduced density matrix (RDM) driven approach of qLR. This allows for the calculation of spectral properties of moderately sized molecules with much larger basis sets than so far possible. We report qLR results for benzene and R-methyloxirane with a cc-pVTZ basis set and study the effect of shot noise on the valence and oxygen K-edge absorption spectra of H2O in the cc-pVTZ basis.
@article{arxiv.2404.16586,
title = {Reduced density matrix formulation of quantum linear response},
author = {Theo Juncker von Buchwald and Karl Michael Ziems and Erik Rosendahl Kjellgren and Stephan P. A. Sauer and Jacob Kongsted and Sonia Coriani},
journal= {arXiv preprint arXiv:2404.16586},
year = {2024}
}