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The Journal of Chemical Physics
Article . 2025 . Peer-reviewed
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Redundant parameter dependencies in conventional and quantum linear response and equation of motion theory for unitary parameterized wave functions

Authors: Erik Rosendahl Kjellgren; Peter Reinholdt; Karl Michael Ziems; Stephan P. A. Sauer; Sonia Coriani; Jacob Kongsted;

Redundant parameter dependencies in conventional and quantum linear response and equation of motion theory for unitary parameterized wave functions

Abstract

Extracting molecular properties from a wave function can be performed through the linear response (LR) formalism or, equivalently, the equation of motion (EOM) formalism. For a simple model system, He in a 6-31G basis, it is shown here that calculated excitation energies depend on the specifically chosen orbitals, even when the ground-state is the FCI solution, if the LR is truncated to a singles expansion. This holds for naïve, projected, self-consistent, and state-transfer parameterizations of the LR operators. With a focus on the state-transfer parameterization, this problem is shown to also hold for more complicated systems and is also present when the LR is truncated to singles and doubles. This problem can be alleviated by performing a ground-state constrained trace optimization of the Hessian matrix before performing the LR calculation. It is finally shown that spectra can be further improved for small LR expansions by targeting only a few states in the constrained trace optimization using constrained state-averaged UCC.

Keywords

linear response theory, /dk/atira/pure/core/keywords/TheFacultyOfScience; name=Faculty of Science, excitation energies, Quantum computing

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
0
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