Explanipedia

Cost-effective scalable quantum error mitigation for tiled Ansätze Open

Erik Rosendahl Kjellgren, Stephan P. A. Sauer, Sonia Coriani, Karl Michael Ziems · 2025

We introduce a cost-effective quantum error mitigation technique that builds on the recent Ansatz-based gate and readout error mitigation method (M0). The technique, tiled M0, leverages the unique structure of tiled Ansätze (e.g., tUPS, QN…

Orbital-Optimized Unitary Coupled Cluster for Indirect Nuclear Spin-Spin Coupling Constants within a Quantum Linear Response Framework Open

Peter Reinholdt, Phillip W. K. Jensen, Stephan P. A. Sauer · 2025

We present a quantum linear response (qLR) approach within an active-space framework for computing indirect nuclear spin-spin coupling constants, a key ingredient in NMR spectra predictions. The method employs the unitary coupled cluster (…

Vibrational corrections to molecular properties including relativistic corrections at the level of the Zeroth-Order Regular Approximation Open

Louise Møller Jessen, Ronan Gleeson, Lars Hemmingsen, Stephan P. A. Sauer · 2025

The vibrational averaging module of the Dalton Project was extended to work also with the Amsterdam Density Functional (ADF) program, making it possible to calculate vibrational corrections to properties and at the same time include a trea…

A Computational Study of the Vibrational and Rotational <i>g</i>-Factors of the Diatomic Molecules LiH, LiF, CO, CS, SiO, and SiS Open

A. Ekstrom, Stephan P. A. Sauer · 2025

The purpose of this article is to present theoretical values for the vibrational and rotational g-factors of several diatomic molecules. The calculations were carried out at the multiconfigurational self-consistent field (MCSCF) lev…

Hyperfine Coupling Constants on Quantum Computers: Performance, Errors, and Future Prospects Open

Phillip W. K. Jensen, Gustav Stausbøll Hedemark, Karl Michael Ziems, Erik Rosendahl Kjellgren, Peter Reinholdt , et al. · 2025

We present the first implementation and computation of electron spin resonance isotropic hyperfine coupling constants (HFCs) on a quantum hardware. As illustrative test cases, we compute the HFCs for the hydroxyl radical (OH^•), …

Reduced density matrix and cumulant approximations of quantum linear response Open

Theo Juncker von Buchwald, Erik Rosendahl Kjellgren, Jacob Kongsted, Stephan P. A. Sauer, Sonia Coriani , et al. · 2025

Linear response (LR) is an important tool in the computational chemist's toolbox. It is therefore no surprise that the emergence of quantum computers has led to a quantum version, quantum LR (qLR). However, the current quantum era of near-…

Substantial Magnetic Fields Arising from Ballistic Ring Currents in Single-Molecule Junctions Open

William Bro‐Jørgensen, Stephan P. A. Sauer, Gemma C. Solomon, Marc H. Garner · 2025

When a small electric bias is applied to a single-molecule junction, current will flow through the molecule via a tunneling mechanism. In molecules with a cyclic or helical structure there may be circular currents, giving rise to a unidire…

Critical Limitations in Quantum-Selected Configuration Interaction Methods Open

Peter Reinholdt, Karl Michael Ziems, Erik Rosendahl Kjellgren, Sonia Coriani, Stephan P. A. Sauer , et al. · 2025

Quantum Selected Configuration Interaction (QSCI) methods (also known as Sample-based Quantum Diagonalization, SQD) have emerged as promising near-term approaches to solving the electronic Schrödinger equation with quantum computers. In th…

Substantial Magnetic Fields Arising from Ballistic Ring Currents in Single-molecule Junctions Open

William Bro‐Jørgensen, Stephan P. A. Sauer, Gemma C. Solomon, Marc H. Garner · 2025

When a small electric bias is applied to a single-molecule junction, current will flow through the molecule via a tunneling mechanism. In molecules with a cyclic or helical structure there may be circular currents, giving rise to a uni-dir…

Redundant parameter dependencies in truncated classic and quantum Linear Response and Equation of Motion theory Open

Stephan P. A. Sauer, Sonia Coriani, Jacob Kongsted · 2025

Extracting molecular properties from a wave function can be done 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 here shown that cal…

Exact closed-form expression for unitary spin-adapted fermionic singlet double excitation operators Open

Erik Rosendahl Kjellgren, Karl Michael Ziems, Peter Reinholdt, Stephan P. A. Sauer, Sonia Coriani , et al. · 2025

We derive exact closed-form expressions for the matrix exponential of the anti-Hermitian spin-adapted singlet double excitation fermionic operators. These expressions enable the efficient implementation of such operators within unitary pro…

RPA(D) and HRPA(D): Calculating NMR Spin–Spin Coupling Constants in Free Amino Acid Residues Open

Christoffer H. S. Møller, Stephan P. A. Sauer · 2025

In the pursuit of computational methods which boast both low computational cost and a high degree of accuracy, the SOPPA‐derived methods RPA(D) and HRPA(D) are showing great promise. This study aims to further the benchmarking of these two…

Reply on RC2 Open

Stephan P. A. Sauer · 2025

Reply on RC1 Open

Stephan P. A. Sauer · 2025

Substantial Magnetic Fields Arising from Ballistic Ring Currents in Single-molecule Junctions Open

William Bro‐Jørgensen, Stephan P. A. Sauer, Gemma C. Solomon, Marc H. Garner · 2025

When a small electric bias is applied to a single- molecule junction, current will flow through the molecule via a tunneling mechanism. In molecules with a cyclic or helical structure there may be circular currents, giving rise to a uni-di…

The Impact of Central Bank Digital Currency on Central Bank Profitability, Risk Taking and Capital Open

Ulrich Bindseil, Marco Marrazzo, Stephan P. A. Sauer · 2025

With digital payments becoming more and more popular, many central banks are investigating the issuance of retail central bank digital currency (CBDC) as a new central bank monetary liability in addition to banknotes and commercial bank re…

Understanding and mitigating noise in molecular quantum linear response for spectroscopic properties on quantum computers Open

Karl Michael Ziems, Erik Rosendahl Kjellgren, Stephan P. A. Sauer, Jacob Kongsted, Sonia Coriani · 2025

Absorption spectra of LiH obtained on a quantum computer using quantum linear response, Pauli saving, QWC, and Ansatz-based read-out and gate error mitigation.

Correction: Schaltz et al. A Theoretical Study of Hydrogen Abstraction Reactions in Guanosine and Uridine. Int. J. Mol. Sci. 2023, 24, 8192 Open

Kasper F. Schaltz, Stephan P. A. Sauer · 2024

In the original publication [...]

Self-consistent Quantum Linear Response with a Polarizable Embedding environment Open

Peter Reinholdt, Erik Rosendahl Kjellgren, Karl Michael Ziems, Sonia Coriani, Stephan P. A. Sauer , et al. · 2024

Quantum computing presents a promising avenue for solving complex problems, particularly in quantum chemistry, where it could accelerate the computation of molecular properties and excited states. This work focuses on hybrid quantum-classi…

A Glycosylation Mechanism Case Study: Unraveling the Mechanism of Stereospecific Self-promoted N -Glycosylations Open

Natasha Videcrantz Faurschou, Stephan P. A. Sauer, Christian Pedersen · 2024

In this study, the mechanism of self-promoted N-glycosylations is extensively investigated through kinetic experiments, computational studies, and nucleophilic competition experiments. Based on the findings, the mechanism is proposed to be…

Divergences in classical and quantum linear response and equation of motion formulations Open

Erik Rosendahl Kjellgren, Peter Reinholdt, Karl Michael Ziems, Stephan P. A. Sauer, Sonia Coriani , et al. · 2024

Calculating molecular properties using quantum devices can be performed through the quantum linear response (qLR) or, equivalently, the quantum equation of motion (qEOM) formulations. Different parameterizations of qLR and qEOM are availab…

Understanding and mitigating noise in molecular quantum linear response for spectroscopic properties on quantum computers Open

Karl Michael Ziems, Erik Rosendahl Kjellgren, Stephan P. A. Sauer, Jacob Kongsted, Sonia Coriani · 2024

The promise of quantum computing to circumvent the exponential scaling of quantum chemistry has sparked a race to develop chemistry algorithms for quantum architecture. However, most works neglect the quantum-inherent shot noise, let alone…

Reduced Density Matrix Formulation of Quantum Linear Response Open

Theo Juncker von Buchwald, Karl Michael Ziems, Erik Rosendahl Kjellgren, Stephan P. A. Sauer, Jacob Kongsted , et al. · 2024

The prediction of spectral properties via linear response (LR) theory is an important tool in quantum chemistry for understanding photoinduced processes in molecular systems. With the advances of quantum computing, we recently adapted this…

Electric Field Gradient Calculations for Ice VIII and IX Using Polarizable Embedding: A Comparative Study on Classical Computers and Quantum Simulators Open

Dániel Nagy, Peter Reinholdt, Phillip W. K. Jensen, Erik Rosendahl Kjellgren, Karl Michael Ziems , et al. · 2024

We test the performance of the polarizable embedding variational quantum eigensolver self-consistent field (PE-VQE-SCF) model for computing electric field gradients with comparisons to conventional complete active space self-consistent-fie…

Divergences in classical and quantum linear response and equation of motion formulations Open

Erik Rosendahl Kjellgren, Peter Reinholdt, Karl Michael Ziems, Stephan P. A. Sauer, Sonia Coriani , et al. · 2024

Calculating molecular properties using quantum devices can be done through the quantum linear response (qLR) or, equivalently, the quantum equation of motion (qEOM) formulations. Different parameterizations of qLR and qEOM are available, n…

Performance of range-separated long-range SOPPA short-range density functional theory method for vertical excitation energies Open

Juliane Holst Fuglsbjerg, Dániel Nagy, Hans Jørgen Aa. Jensen, Stephan P. A. Sauer · 2024

In this paper, benchmark results are presented on the calculation of vertical electronic excitation energies using a long-range second-order polarization propagator approximation (SOPPA) description with a short-range density functional th…

On the geometry dependence of the nuclear magnetic resonance chemical shift of mercury in thiolate complexes: A relativistic density functional theory study Open

Haide Wu, Lars Hemmingsen, Stephan P. A. Sauer · 2024

Thiolate containing mercury(II) complexes of the general formula [Hg(SR) ] have been of great interest since the toxicity of mercury was recognized. 199 Hg nuclear magnetic resonance spectroscopy (NMR) is a powerful tool for characterizati…

Subspace Methods for the Simulation of Molecular Response Properties on a Quantum Computer Open

Peter Reinholdt, Erik Rosendahl Kjellgren, Juliane Holst Fuglsbjerg, Karl Michael Ziems, Sonia Coriani , et al. · 2024

We explore Davidson methods for obtaining excitation energies and other linear response properties within the recently developed quantum self-consistent linear response (q-sc-LR) method. Davidson-type methods allow for obtaining only a few…

The variational quantum eigensolver self-consistent field method within a polarizable embedded framework Open

Erik Rosendahl Kjellgren, Peter Reinholdt, Aaron Fitzpatrick, N. Walter Talarico, Phillip W. K. Jensen , et al. · 2024

We formulate and implement the Variational Quantum Eigensolver Self Consistent Field (VQE-SCF) algorithm in combination with polarizable embedding (PE), thereby extending PE to the regime of quantum computing. We test the resulting algorit…

The Importance of Anharmonicity and Solvent Effects on the OH Radical Attack on Nucleobases Open

A. Ekstrom, Vera Staun Hansen, Stephan P. A. Sauer · 2024

Previous theoretical investigations of the reactions between an OH radical and a nucleobase have stated the most important pathways to be the C5-C6 addition for pyrimidines and the C8 addition for purines. Furthermore, the abstraction of a…

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