One-Body Properties and their Perturbative Accuracy with Aufbau Suppressed Coupled Cluster Theory

Oct 26, 2026

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The paper derives and implements the one-body reduced density matrix calculation for Aufbau suppressed coupled cluster (ASCC). Using excited-state natural orbitals from the 1-RDM, it refines ASCC solutions for valence and Rydberg systems by repeatedly solving ASCC equations in successive natural-orbital bases to reduce dependence on initial molecular orbitals. For small molecules with available high-level benchmarks, ASCC dipole moments match linear response and equation-of-motion coupled cluster accuracy when perturbative completeness is preserved.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages24

Reading Time1 h 0 min

AccessFree to download

Introduction

State-specific excited-state methods and their limitations

ASCC motivation and comparison to linear response approaches

One-body properties from the 1-RDM and analytic derivatives

arXiv :2512 .07804v2 [physics .chem-ph] 19 Mar 2026 One-Body Properties and their Perturbative Accuracy with Aufbau Suppressed Coupled Cluster Theory Conor Bready,1 Harrison Tuckman,1 and Eric Neuscamman1, 2, a) 1) Department of Chemistry, University of California, Berkeley, California 94720, USA 2) Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA (Dated: 20 March 2026) We derived and implemented the calculation of the one-body reduced density matrix for Aufbau suppressed coupled cluster theory, from which excited state natural orbitals and one-body properties, like atomic populations and dipole moments, are obtained. We utilized the natural orbitals to refine the ASCC solution for simple valence and Rydberg systems, exploring the process of repeatedly solving the ASCC equations in successive natural orbital bases to achieve independence from the starting molecular orbitals. For dipole moments in small molecules where high-level comparison data is available, we find that the accuracy of ASCC essentially matches that of linear response and equation-of-motion coupled cluster as long as care is taken topreserve the response’s perturbative completeness. I. INTRODUCTION The proper manipulation of electronic excited states to perform intended chemical tasks requires knowledge of both the necessary excitation energy and the characteristic properties of the desired state. Many linear responsebased methods such as time dependent density functional theory (TD-DFT) 1–3 and equation of motion coupled cluster theory (EOM-CC)4–6 are able to provide both energies and properties quite accurately.7–9 However, these linear response methods, unlike state-specific methods, are dependent upon the proper behavior of the ground state, which has the potential to be problematic when the excited state’s optimal geometry is far from that of the ground state’s.10 , 11 Approaches such as the spinflip method for both TD-DFT 12 , 13 and EOM-CC, 14 , 15 or double ionization potential and double electron affinity for just EOM-CC, 16–21 help ameliorate the problems that arise due to this multi-configurational character while still maintaining a single-reference formalism; however, this requires chemical knowledge that the newly chosen reference must itself remain well-behaved at the interested geometry. On the other hand, Aufbau suppressed coupled cluster (ASCC)22 provides a state-specific approach, bypassing the reliance that a different potential energy surface still yields reasonable results. Furthermore, ASCC maintains all of the benefits of coupled cluster theory (CC), providing an interesting candidate for the evaluation of excited state properties. After some adjustments informed by extending the perturbative analysis performed by Tuckman et al.23 to property evaluations, we demonstrate that ASCC’s response can be just as accurate as other excited state CC counterparts, with the potential to be more accurate for charge transfer systems where ASCC has previously excelled.24 In addition to the benefits of state-specific methods when exploring structures outside of their optimal ground a) Electronic mail: [eneuscamman@berkeley.edu](eneuscamman@berkeley.edu) state geometries, these methods also have the benefits of orbital relaxations tailored to the excited state itself. Many approaches utilize this concept of trying to optimize the excited state orbitals, including various methods in DFT,25–42 CASSCF,43–48 CI,49–56 perturbation theory,57–59 CC,60–65 variational Monte Carlo,66–77 and more. Likewise, ASCC was recently shown to benefit from its intrinsic orbital relaxations by demonstrating near independence from the reference provided.78 Generically, utilizing state-specific orbitals often results in amore accurate description of the excited state itself and is therefore incredibly valuable when comparing to experiments. Derivatives of this accurate energy expression with respect to one-body per

FAQs

What does the paper implement for Aufbau suppressed coupled cluster theory?

It derives and implements the calculation of the one-body reduced density matrix (1-RDM) for ASCC, enabling excited-state natural orbitals and one-body properties.

How are ASCC solutions refined to reduce dependence on starting orbitals?

The natural orbitals are used to iteratively solve ASCC equations in successive natural-orbital bases, aiming for independence from the initial molecular orbitals.

How accurate are ASCC dipole moments compared with other coupled-cluster approaches?

For small molecules with high-level comparison data, ASCC dipole moments match the accuracy of linear response and equation-of-motion coupled cluster, provided perturbative completeness is maintained.

Oct 26, 2026

Upload by Damian