Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2609.13098

Accelerating Periodic Coupled Cluster and Algebraic Diagrammatic Construction Theories With Frozen Natural Orbitals

Ning-Yuan Chen, James D. Serna, Alexander Yu. Sokolov

Published Sep 11, 2026• 0 citations
arXivHTMLPDF

Abstract

We present a unified frozen natural orbital (FNO) framework for periodic Gaussian-orbital post-Hartree-Fock calculations with explicit k-point sampling. The approach includes conventional ground-state FNOs together with state-specific (SS-FNO) and state-averaged (SA-FNO) variants constructed from perturbative one-particle density matrices. We implement these approximations for periodic Moller-Plesset perturbation theory, algebraic diagrammatic construction, and equation-of-motion coupled cluster methods in the PySCF software package and benchmark them for correlation energies, equations of state, fundamental band gaps, and quasiparticle band structures of semiconductors and insulators. FNO truncation reproduces canonical results with small errors while substantially reducing computational cost. SS-FNO enables accurate large-basis band-gap calculations, including quadruple-zeta results, whereas SA-FNO efficiently compresses the virtual space for multi-state band-structure calculations. Combined with basis-set and thermodynamic-limit extrapolations, the framework provides a practical route to high-accuracy correlated calculations in periodic systems.

DOI
10.48550/arxiv.2609.13098

Related papers

Open-shell frozen natural orbital approach for quantum eigensolvers

Angela F. Harper, Xiaobing Liu, Scott N. Genin +1 more

We present an open-shell frozen natural orbital (FNO) approach, which utilizes the second-order Z-averaged perturbation theory (ZAPT2), to reduce the restricted open-shell Hartree-Fock virtual space size with controllable accuracy. Our ZAPT2 frozen natural orbital (ZAPT-FNO) selection scheme significantly outperforms the canonical molecular orbital virtual space truncation scheme based on Hartree-Fock orbital energies, especially when using large multiple-polarized and augmented basis sets. We demonstrate that the ZAPT-FNO-selected virtual orbitals lead to a systematic convergence of the correlation energies but, more importantly, to the singlet-triplet T1-S0 energy gaps with respect to the complete active space (CAS) [occupied + virtual] size. We confirm our findings by simulating T1-S0 gaps in H2O2 and O2 molecules using the traditional complete active space configuration interaction (CASCI) approach, as well as in stretched CH2, for which we also employed the iterative qubit coupled cluster (iQCC) method as a quantum eigensolver. Finally, we applied the iQCC method with a ZAPT-FNO-selected active space to the phosphorescent Ir(ppy)3 complex with 260 electrons, where extended basis sets are required to achieve chemical (∼1 mEh) accuracy. In this case, CASCI results are not available; however, the iQCC-computed T1-S0 gaps show robust convergence with an enlarging basis set and CAS size, approaching the experimental value. Thus, the ZAPT-FNO method is very promising for improving the accuracy of quantum chemical modeling in a resource-efficient manner and opens the door to simulating open-shell states of large materials within realistic active space sizes and without compromising on basis-set quality.

arXiv:2511.13677•The Journal of Chemical Physics•Apr 15, 2026•0 citations

Frozen Natural Orbitals for the State-Averaged Driven Similarity Renormalization Group

Chenyang Li, Shuxian Mao, Renke Huang +1 more

We present a reduced-cost implementation of the state-averaged driven similarity renormalization group (SA-DSRG) based on the frozen natural orbital (FNO) approach. The natural orbitals (NOs) are obtained by diagonalizing the one-body reduced density matrix from SA-DSRG second-order perturbation theory (SA-DSRG-PT2). We consider three criteria to truncate the virtual NOs for the subsequent electron correlation treatment beyond SA-DSRG-PT2. An additive second-order correction is applied to the SA-DSRG Hamiltonian to reintroduce correlation effects from the discarded orbitals. The FNO SA-DSRG method is benchmarked on 35 small organic molecules in the QUEST database. When keeping 98–99% of the cumulative occupation numbers, the mean absolute error in the vertical transition energies due to FNO is less than 0.01 eV. Using the same FNO threshold, we observe a speedup of 9 times compared to the conventional SA-DSRG implementation for nickel carbonyl with a quadruple-ζ basis set. The FNO approach enables nonperturbative SA-DSRG computations on chloroiron corrole [FeCl(C 19 H 11 N 4 )] with more than 1000 basis functions, surpassing the current limit of a conventional implementation.

arXiv:2312.07008•Journal of Chemical Theory and Computation•May 15, 2024•5 citations

Frozen natural orbitals for projection-based embedding method and its application to quantum computation

Tong Cheng, Jun Zeng, Minghui Yang

Projection-based embedding offers a robust framework for modeling chemical processes in large molecular systems. It partitions computations into low-level treatments for the environmental subsystems and high-level treatments for the active subsystems. To address the computational bottleneck of applying high-accuracy wavefunction theory to the active regions, we introduce frozen natural orbitals (FNOs) approach. This technique efficiently compresses the virtual orbital space to generate a compact set of natural orbitals, which significantly accelerates the convergence of correlation energy recovery. We evaluated the FNO-based embedding approach in comparison with two alternative virtual space truncation approaches for a diverse range of molecular systems. Our results demonstrate that the FNO-embedded method exhibits superior performance by delivering accurate correlation energies with a substantially fewer number of virtual orbitals. Its potential for quantum computing is also discussed, as this reduction in orbitals can be directly translated to lower qubit requirements and thereby facilitate the quantum simulations on near-term quantum hardware.

The Journal of Chemical Physics•Mar 18, 2026•0 citations

Scaling up electronic structure calculations on quantum computers: The frozen natural orbital based method of increments

Prakash Verma, Lee M. J. Huntington, Marc P. Coons +3 more

The method of increments and frozen natural orbital (MI-FNO) framework is introduced to help expedite the application of noisy, intermediate-scale quantum (NISQ) devices for quantum chemistry simulations. The MI-FNO framework provides a systematic reduction of the occupied and virtual orbital spaces for quantum chemistry simulations. The correlation energies of the resulting increments from the MI-FNO reduction can then be solved by various algorithms, including quantum algorithms such as the phase estimation algorithm and the variational quantum eigensolver (VQE). The unitary coupled-cluster singles and doubles VQE framework is used to obtain correlation energies for the case of small molecules (i.e., BeH2, CH4, NH3, H2O, and HF) using the cc-pVDZ basis set. The quantum resource requirements are estimated for a constrained geometry complex catalyst that is utilized in industrial settings for the polymerization of α-olefins. We show that the MI-FNO approach provides a significant reduction in the quantum bit (qubit) requirements relative to the full system simulations. We propose that the MI-FNO framework can create scalable examples of quantum chemistry problems that are appropriate for assessing the progress of NISQ devices.

arXiv:2002.07901•The Journal of Chemical Physics•Jul 16, 2021•25 citations

Exploring the accuracy of the equation-of-motion coupled-cluster band gap of solids

Evgeny Moerman, Henrique Pereira Coutada Miranda, Alejandro Gallo +7 more

While the periodic equation-of-motion coupled-cluster (EOM-CC) method promises systematic improvement of electronic band gap calculations in solids, its practical application at the singles and doubles level (EOM-CCSD) is hindered by severe finite-size errors in feasible simulation cells. We present a hybrid approach combining EOM-CCSD with the computationally less demanding G W approximation to estimate thermodynamic limit band gaps for several insulators and semiconductors. Our method substantially reduces required cell sizes while maintaining accuracy. Comparisons with experimental gaps and self-consistent G W calculations reveal that deviations in EOM-CCSD predictions correlate with reduced single excitation character of the excited many-electron states. Our work not only provides a computationally tractable approach to EOM-CC calculations in solids but also reveals fundamental insights into the role of single excitations in electronic-structure theory.

arXiv:2501.18667•Physical review. B./Physical review. B•Mar 26, 2025•9 citations

Resolving finite-size errors in EOM-CCSD band gaps of solids with interacting-bath dynamical embedding theory

Jiachen Li, Christopher Hillenbrand, Christian Venturella +2 more

Periodic equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD) has shown promise for quantitative calculations of band structures in solids. However, its steep computational scaling has limited calculations to relatively coarse k-point meshes, leading to sizable finite-size errors and discrepant estimates of thermodynamic-limit band gaps in recent benchmarks. In this work, we revisit EOM-CCSD band gaps for ten semiconductors and insulators using interacting-bath dynamical embedding theory (ibDET), a systematically improvable Green's function embedding framework that enables dense Brillouin-zone sampling at modest computational cost. By pushing the k-point sampling up to 10 × 10 × 10, well beyond the system sizes accessible in canonical periodic EOM-CCSD calculations, we significantly reduce finite-size errors and obtain stable thermodynamic-limit extrapolations. We further compare G0W0@PBE, G0W0@HF, and EOM-CCSD on an equal footing using the same numerical settings in PySCF. We find that EOM-CCSD yields a mean absolute error of 0.32 eV relative to experimental band gaps for a test set of ten semiconductors and insulators, which is lower than that of G0W0@PBE. For ZnO, EOM-CCSD also accurately describes the Zn 3d-band binding energy, despite overestimating the band gap. These results demonstrate that ibDET offers a practical route to high-accuracy many-body electronic structure calculations in periodic systems.

arXiv:2606.12621•The Journal of Chemical Physics•Sep 1, 2026•0 citations
We present a unified frozen natural orbital (FNO) framework for periodic Gaussian-orbital post-Hartree-Fock calculations with explicit k-point sampling. The approach includes conventional ground-state FNOs together with state-specific (SS-FNO) and state-averaged (SA-FNO) variants constructed from perturbative one-particle density matrices. We implement these approximations for periodic Moller-Plesset perturbation theory, algebraic diagrammatic construction, and equation-of-motion coupled cluster methods in the PySCF software package and benchmark them for correlation energies, equations of state, fundamental band gaps, and quasiparticle band structures of semiconductors and insulators. FNO truncation reproduces canonical results with small errors while substantially reducing computational cost. SS-FNO enables accurate large-basis band-gap calculations, including quadruple-zeta results, whereas SA-FNO efficiently compresses the virtual space for multi-state band-structure calculations. Combined with basis-set and thermodynamic-limit extrapolations, the framework provides a practical route to high-accuracy correlated calculations in periodic systems.
We present an open-shell frozen natural orbital (FNO) approach, which utilizes the second-order Z-averaged perturbation theory (ZAPT2), to reduce the restricted open-shell Hartree-Fock virtual space size with controllable accuracy. Our ZAPT2 frozen natural orbital (ZAPT-FNO) selection scheme significantly outperforms the canonical molecular orbital virtual space truncation scheme based on Hartree-Fock orbital energies, especially when using large multiple-polarized and augmented basis sets. We demonstrate that the ZAPT-FNO-selected virtual orbitals lead to a systematic convergence of the correlation energies but, more importantly, to the singlet-triplet T1-S0 energy gaps with respect to the complete active space (CAS) [occupied + virtual] size. We confirm our findings by simulating T1-S0 gaps in H2O2 and O2 molecules using the traditional complete active space configuration interaction (CASCI) approach, as well as in stretched CH2, for which we also employed the iterative qubit coupled cluster (iQCC) method as a quantum eigensolver. Finally, we applied the iQCC method with a ZAPT-FNO-selected active space to the phosphorescent Ir(ppy)3 complex with 260 electrons, where extended basis sets are required to achieve chemical (∼1 mEh) accuracy. In this case, CASCI results are not available; however, the iQCC-computed T1-S0 gaps show robust convergence with an enlarging basis set and CAS size, approaching the experimental value. Thus, the ZAPT-FNO method is very promising for improving the accuracy of quantum chemical modeling in a resource-efficient manner and opens the door to simulating open-shell states of large materials within realistic active space sizes and without compromising on basis-set quality.
We present a reduced-cost implementation of the state-averaged driven similarity renormalization group (SA-DSRG) based on the frozen natural orbital (FNO) approach. The natural orbitals (NOs) are obtained by diagonalizing the one-body reduced density matrix from SA-DSRG second-order perturbation theory (SA-DSRG-PT2). We consider three criteria to truncate the virtual NOs for the subsequent electron correlation treatment beyond SA-DSRG-PT2. An additive second-order correction is applied to the SA-DSRG Hamiltonian to reintroduce correlation effects from the discarded orbitals. The FNO SA-DSRG method is benchmarked on 35 small organic molecules in the QUEST database. When keeping 98–99% of the cumulative occupation numbers, the mean absolute error in the vertical transition energies due to FNO is less than 0.01 eV. Using the same FNO threshold, we observe a speedup of 9 times compared to the conventional SA-DSRG implementation for nickel carbonyl with a quadruple-ζ basis set. The FNO approach enables nonperturbative SA-DSRG computations on chloroiron corrole [FeCl(C 19 H 11 N 4 )] with more than 1000 basis functions, surpassing the current limit of a conventional implementation.
Projection-based embedding offers a robust framework for modeling chemical processes in large molecular systems. It partitions computations into low-level treatments for the environmental subsystems and high-level treatments for the active subsystems. To address the computational bottleneck of applying high-accuracy wavefunction theory to the active regions, we introduce frozen natural orbitals (FNOs) approach. This technique efficiently compresses the virtual orbital space to generate a compact set of natural orbitals, which significantly accelerates the convergence of correlation energy recovery. We evaluated the FNO-based embedding approach in comparison with two alternative virtual space truncation approaches for a diverse range of molecular systems. Our results demonstrate that the FNO-embedded method exhibits superior performance by delivering accurate correlation energies with a substantially fewer number of virtual orbitals. Its potential for quantum computing is also discussed, as this reduction in orbitals can be directly translated to lower qubit requirements and thereby facilitate the quantum simulations on near-term quantum hardware.
The method of increments and frozen natural orbital (MI-FNO) framework is introduced to help expedite the application of noisy, intermediate-scale quantum (NISQ) devices for quantum chemistry simulations. The MI-FNO framework provides a systematic reduction of the occupied and virtual orbital spaces for quantum chemistry simulations. The correlation energies of the resulting increments from the MI-FNO reduction can then be solved by various algorithms, including quantum algorithms such as the phase estimation algorithm and the variational quantum eigensolver (VQE). The unitary coupled-cluster singles and doubles VQE framework is used to obtain correlation energies for the case of small molecules (i.e., BeH2, CH4, NH3, H2O, and HF) using the cc-pVDZ basis set. The quantum resource requirements are estimated for a constrained geometry complex catalyst that is utilized in industrial settings for the polymerization of α-olefins. We show that the MI-FNO approach provides a significant reduction in the quantum bit (qubit) requirements relative to the full system simulations. We propose that the MI-FNO framework can create scalable examples of quantum chemistry problems that are appropriate for assessing the progress of NISQ devices.
While the periodic equation-of-motion coupled-cluster (EOM-CC) method promises systematic improvement of electronic band gap calculations in solids, its practical application at the singles and doubles level (EOM-CCSD) is hindered by severe finite-size errors in feasible simulation cells. We present a hybrid approach combining EOM-CCSD with the computationally less demanding G W approximation to estimate thermodynamic limit band gaps for several insulators and semiconductors. Our method substantially reduces required cell sizes while maintaining accuracy. Comparisons with experimental gaps and self-consistent G W calculations reveal that deviations in EOM-CCSD predictions correlate with reduced single excitation character of the excited many-electron states. Our work not only provides a computationally tractable approach to EOM-CC calculations in solids but also reveals fundamental insights into the role of single excitations in electronic-structure theory.
Periodic equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD) has shown promise for quantitative calculations of band structures in solids. However, its steep computational scaling has limited calculations to relatively coarse k-point meshes, leading to sizable finite-size errors and discrepant estimates of thermodynamic-limit band gaps in recent benchmarks. In this work, we revisit EOM-CCSD band gaps for ten semiconductors and insulators using interacting-bath dynamical embedding theory (ibDET), a systematically improvable Green's function embedding framework that enables dense Brillouin-zone sampling at modest computational cost. By pushing the k-point sampling up to 10 × 10 × 10, well beyond the system sizes accessible in canonical periodic EOM-CCSD calculations, we significantly reduce finite-size errors and obtain stable thermodynamic-limit extrapolations. We further compare G0W0@PBE, G0W0@HF, and EOM-CCSD on an equal footing using the same numerical settings in PySCF. We find that EOM-CCSD yields a mean absolute error of 0.32 eV relative to experimental band gaps for a test set of ten semiconductors and insulators, which is lower than that of G0W0@PBE. For ZnO, EOM-CCSD also accurately describes the Zn 3d-band binding energy, despite overestimating the band gap. These results demonstrate that ibDET offers a practical route to high-accuracy many-body electronic structure calculations in periodic systems.