Reference excitation energies of increasingly large molecules: a QMC study of cyanine dyes

Alice Cuzzocrea; Saverio Moroni; Anthony Scemama; Claudia Filippi

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arXiv · 2111.09640

Reference excitation energies of increasingly large molecules: a QMC study of cyanine dyes

Alice Cuzzocrea·Saverio Moroni·Anthony Scemama·Claudia Filippi

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Abstract

We revisit here the lowest vertical excitations of cyanine dyes using quantum Monte Carlo and leverage on recent developments to systematically improve on previous results. In particular, we employ a protocol for the construction of compact and accurate multi-determinant Jastrow-Slater wave functions for multiple states, which we have recently validated on the excited-state properties of several small prototypical molecules. Here, we obtain quantum Monte Carlo excitation energies in excellent agreement with high-level coupled cluster for all the cyanines where the coupled cluster method is applicable. Furthermore, we push our protocol to longer chains, demonstrating that quantum Monte Carlo is a viable methodology to establish reference data at system sizes which are hard to reach with other high-end approaches of similar accuracy. Finally, we determine which ingredients are key to an accurate treatment of these challenging systems and rationalize why a description of the excitation based on only active $π$ orbitals lacks the desired accuracy for the shorter chains.

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Alice Cuzzocrea, Saverio Moroni, Anthony Scemama, Claudia Filippi. 2021-11-19. Reference excitation energies of increasingly large molecules: a QMC study of cyanine dyes. https://arxiv.org/abs/2111.09640

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