Article
Chemistry, Physical
Sarai Dery Folkestad, Henrik Koch
Summary: In this work, we extend the multilevel coupled cluster framework to include triplet excitation energies and use approximate correlated natural transition orbitals (CNTOs) to generate active orbitals. The multilevel approach provides computational savings while maintaining high accuracy. We compare the performance of MLCCSD and MLCC2 to their standard coupled cluster counterparts and demonstrate proof-of-concept calculations of singlet-triplet gaps for potential use in organic light-emitting diodes.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2023)
Article
Chemistry, Physical
Soumi Haldar, Tamoghna Mukhopadhyay, Achintya Kumar Dutta
Summary: The article presents a novel and cost-effective approach to improve the CC2 model by using a second similarity transformation of the Hamiltonian to include higher-order terms. The newly developed ST-EOM-CC2 model shows significant improvement in excitation energies of Rydberg and charge-transfer excited states while retaining good performance for valence excited states.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Diata Traore, Emmanuel Giner, Julien Toulouse
Summary: The basis-set correction method based on density-functional theory corrects the energy calculated by a wave-function method with a given basis set by a density functional. This method accelerates the convergence of ground-state energies to the complete-basis-set limit by incorporating short-range electron correlation effects missing in the basis set. In this work, the method is extended to a linear-response formalism for calculating excited-state energies, and it is shown to significantly accelerate the basis convergence of excited-state total energies.
JOURNAL OF CHEMICAL PHYSICS
(2023)
Article
Chemistry, Physical
F. D. Vila, K. Kowalski, B. Peng, J. J. Kas, J. J. Rehr
Summary: The challenging many-body excitations in X-ray photoemission spectra have been addressed with a novel cumulant-based method that extends to double excitations. Experimental results demonstrate that the double contributions can reduce errors in core binding energy and improve the quasiparticle-satellite gap.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2022)
Article
Chemistry, Physical
Ciro A. Guido, Amara Chrayteh, Giovanni Scalmani, Benedetta Mennucci, Denis Jacquemin
Summary: The computational protocol cLR(2) effectively describes solvatochromism and fluorosolvatochromism by coupling the polarizable continuum model with time-dependent density functional theory. It is especially beneficial for modeling bright excitations with significant charge-transfer character and cases where an accurate balance between states of various polarities should be restored.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2021)
Article
Chemistry, Physical
A. J. C. Varandas
Summary: This study discusses the relationship between cost-effectiveness and accuracy in electronic structure calculations, utilizing advanced computational tools and methods to enhance precision and efficiency. By developing accurate hybrid post-CBS extrapolation schemes and validating their effectiveness, the approach proposed here shows promise for high-accuracy quantum chemistry, with further improvements and considerations for efficiency.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2021)
Article
Chemistry, Physical
Andreas Dreuw, Antonia Papapostolou, Adrian L. Dempwolff
Summary: Algebraic diagrammatic construction (ADC) schemes are ab initio methods that can calculate excited electronic states and electron-detached and -attached states. These methods have great potential for molecular applications such as calculating absorption spectra, photoelectron spectra, and electron attachment processes. ADC originates from Green's function or propagator theory, but recent developments heavily rely on intermediate state representation or effective Liouvillian formalisms. The different approaches for calculating excitation energies, ionization potentials, and electron affinities are related and provide a consistent description of these quantities at equivalent theory levels with comparable errors. Most quantum chemical program packages include ADC methods, but the most complete ADC suite of methods can be found in the recent release of Q-Chem.
JOURNAL OF PHYSICAL CHEMISTRY A
(2023)
Article
Chemistry, Physical
Simon Thomas, Florian Hampe, Stella Stopkowicz, Juergen Gauss
Summary: In this paper, we discuss the mathematical perspective on the occurrence of complex energy values in coupled-cluster calculations, showing that ground-state energy is generally real in the presence of real-valued Hamiltonian matrices, and complex excitation energies mainly occur in conical intersections. Symmetry can prevent the occurrence of complex energy values in complex Hamiltonian systems, and the real part of complex energy values can serve as a good approximation to the full configuration-interaction energy.
Article
Chemistry, Multidisciplinary
Hector H. Corzo, Andreas Erbs Hillers-Bendtsen, Ashleigh Barnes, Abdulrahman Y. Zamani, Filip Pawlowski, Jeppe Olsen, Poul Jorgensen, Kurt V. Mikkelsen, Dmytro Bykov
Summary: This study addresses the computational challenges of investigating complex chemical systems using ab-initio methodologies. The researchers introduce the Divide-Expand-Consolidate (DEC) approach, which is a linear-scaling, massively parallel framework, as a viable solution for coupled cluster (CC) theory. They also present the cluster perturbation theory to mitigate the inherent limitations of DEC. Furthermore, they propose the CPS (D-3) model, derived from a CC singles parent and a doubles auxiliary excitation space, for efficient computation of excitation energies in large molecular systems. Overall, this study provides new algorithms and frameworks that can significantly improve the calculation of molecular properties.
FRONTIERS IN CHEMISTRY
(2023)
Article
Chemistry, Physical
Niels Kristian Madsen, Rasmus Berg Jensen, Ove Christiansen
Summary: The first implementation of tensor-decomposed vibrational coupled cluster response theory for calculating vibrational excitation energies is presented in this study, where the CP-VCC algorithm has been generalized to allow transformations with the Jacobian matrix and a new eigenvalue solver is introduced. Numerical results show that errors introduced by tensor decomposition can be controlled by numerical thresholds, and the approach allows for black-box calculations with minimal user input. Efficient computation of eigenstates of PAHs without explicitly constructed tensors is also demonstrated, improving memory and CPU time compared to full-tensor versions.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Mathematics
Jin-Cai Kang, Xiao-Qi Liu, Chun-Lei Tang
Summary: In this study, we investigate the coupling of the Schrodinger equation with a neutral scalar field in non-radial symmetric space H-1(R-2). By employing the Nehari manifold, Moser iteration, and some analytical techniques, we obtain a positive ground state solution to the problem that is both classical and spherically symmetric. The solution and its derivatives up to order 2 exhibit exponential decay at infinity. Additionally, we analyze the asymptotic behavior of the solutions in the sense of the Chern-Simons limit. Our work serves as a supplement and extension to the research conducted by Han et al. (2014) [12], where they heavily rely on the symmetry of the workspace.
JOURNAL OF DIFFERENTIAL EQUATIONS
(2023)
Article
Chemistry, Physical
Edward F. Valeev, Robert J. Harrison, Adam A. Holmes, Charles C. Peterson, Deborah A. Penchoff
Summary: Optimizing nearly exact orthonormal orbitals in real space using a multiresolution spectral element basis allows for evaluation of energy of arbitrary states of atoms and molecules. This method provides more accurate electronic energies compared to Gaussian AO bases, and is suitable for high-end models of correlated electronic states. The approach can optimize over 100 fully correlated numerical orbitals on a single computer node, with significant room for improvement.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2023)
Article
Chemistry, Physical
Antoine Marie, Fabris Kossoski, Pierre-Francois Loos
Summary: In this study, the structure of the energy landscape of variational CC is explored and compared with the traditional version. By investigating two model systems under weak and strong correlation conditions, the performance of variational pCCD (VpCCD) and traditional pCCD is evaluated against their CI equivalent.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Chemistry, Physical
Iryna Knysh, Jose D. J. Villalobos-Castro, Ivan Duchemin, Xavier Blase, Denis Jacquemin
Summary: The change of molecular dipole moment induced by photon absorption is important for interpreting optical spectra. While time-dependent density functional theory (TD-DFT) is commonly used to predict excited-state dipoles (mu(ES)), this study shows that the many-body Green's function Bethe-Salpeter equation (BSE) is a valuable alternative with decreased dependency on exchange-correlation functional. The BSE method is not only suitable for transition energies and oscillator strengths, but also for properties related to the excited-state density.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2023)
Article
Chemistry, Physical
Dipanjali Halder, V. S. Prasannaa, Rahul Maitra
Summary: In this paper, a unitary variant of a double exponential coupled cluster theory is developed to handle molecular strong correlation with arbitrary electronic complexity. Using the Hartree-Fock determinant as the reference, the theory introduces a sequential product of parameterized unitary Ansatze, making the implementation simpler in classical computers and hybrid quantum-classical variational quantum eigensolver frameworks.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Timais Janz, Manuel Gueterbock, Fabian Mueller, Martin Quick, Ilya N. Ioffe, Florian A. Bischoff, Sergey A. Kovalenko
Article
Chemistry, Physical
Jakob S. Kottmann, Florian A. Bischoff, Edward F. Valeev
JOURNAL OF CHEMICAL PHYSICS
(2020)
Article
Chemistry, Physical
Sebastian Radunz, Werner Kraus, Florian A. Bischoff, Franziska Emmerling, Harald Rune Tschiche, Ute Resch-Genger
JOURNAL OF PHYSICAL CHEMISTRY A
(2020)
Article
Chemistry, Physical
Marc Reimann, Florian A. Bischoff, Joachim Sauer
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2020)
Article
Chemistry, Multidisciplinary
Fabian Mueller, Julius B. Stueckrath, Florian A. Bischoff, Laura Gagliardi, Joachim Sauer, Sreekanta Debnath, Marcel Jorewitz, Knut R. Asmis
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2020)
Article
Quantum Science & Technology
Phillip W. K. Jensen, Lasse Bjorn Kristensen, Jakob S. Kottmann, Alan Aspuru-Guzik
Summary: The study introduces a quantum algorithm that samples the set of energies within a target energy-interval without the need for good approximations of the target energy-eigenstates. Initial applications involve amplifying excited states on molecular hydrogen, with resource and runtime estimates provided for direct and iterative amplification protocols.
QUANTUM SCIENCE AND TECHNOLOGY
(2021)
Article
Chemistry, Physical
Jakob S. Kottmann, Philipp Schleich, Teresa Tamayo-Mendoza, Alan Aspuru-Guzik
Summary: This study introduces a basis-set-free approach for the variational quantum eigensolver, utilizing an adaptive representation of molecular wave functions to directly determine system-specific representations of qubit Hamiltonians without globally defined basis sets. The use of pair-natural orbitals at the level of second-order perturbation theory results in compact qubit Hamiltonians with high numerical accuracy. Initial applications with compact Hamiltonians on up to 22 qubits have been demonstrated, showing reductions in quantum circuits through the structure of the pair-natural orbitals.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2021)
Article
Quantum Science & Technology
Zi-Jian Zhang, Thi Ha Kyaw, Jakob S. Kottmann, Matthias Degroote, Alan Aspuru-Guzik
Summary: This work presents a method for constructing reduced-size entangler pools leveraging classical algorithms, which ranks and screens entanglers based on mutual information between qubits in classically approximated ground state. Numerical experiments demonstrate that a reduced entangler pool can achieve the same numerical accuracy as the original pool, paving a new way for adaptive construction of ansatz circuits in variational quantum algorithms.
QUANTUM SCIENCE AND TECHNOLOGY
(2021)
Article
Chemistry, Physical
Julius B. Stueckrath, Florian A. Bischoff
Summary: This study presents a highly accurate numerical implementation for computing molecular Kohn-Sham effective potentials based on a Hartree-Fock wavefunction and density, using the RKS approach. The method represents potentials and orbitals in a multiresolution wavelet basis to avoid issues related to basis set incompleteness, and successfully removes oscillating potentials. The implementation allows for the generation of benchmark quality molecular Kohn-Sham potentials, with a special emphasis on the role of nodal planes in calculations demonstrated in HCN and benzene.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2021)
Article
Quantum Science & Technology
Jakob S. Kottmann, Sumner Alperin-Lea, Teresa Tamayo-Mendoza, Alba Cervera-Lierta, Cyrille Lavigne, Tzu-Ching Yen, Vladyslav Verteletskyi, Philipp Schleich, Abhinav Anand, Matthias Degroote, Skylar Chaney, Maha Kesibi, Naomi Grace Curnow, Brandon Solo, Georgios Tsilimigkounakis, Claudia Zendejas-Morales, Artur F. Izmaylov, Alan Aspuru-Guzik
Summary: Variational quantum algorithms are promising for near-term quantum computers, but lack standardized methods in algorithmic development. Heuristics are crucial, leading to a high demand for flexible and reliable ways to implement, test, and share new ideas. tequila is a Python development package designed for fast and flexible implementation, prototyping, and deployment of novel quantum algorithms.
QUANTUM SCIENCE AND TECHNOLOGY
(2021)
Article
Quantum Science & Technology
Jakob S. Kottmann, Mario Krenn, Thi Ha Kyaw, Sumner Alperin-Lea, Alan Aspuru-Guzik
Summary: The parameters of quantum systems grow exponentially with the number of particles, posing challenges to numerical simulations on classical computers. The concept of quantum computer designed quantum hardware is applied to quantum optics to address limitations in quantum device design and verification due to small system sizes. By mapping complex experimental setups to gate-based quantum circuits, digital quantum simulation of experiments and designing setups for entangled photonic systems are explored, promising to be a useful tool for future quantum device design.
QUANTUM SCIENCE AND TECHNOLOGY
(2021)
Article
Chemistry, Physical
Sreekanta Debnath, Marcel Jorewitz, Knut R. Asmis, Fabian Mueller, Julius B. Stueckrath, Florian A. Bischoff, Joachim Sauer
Summary: The infrared photodissociation spectra of He-tagged (Al2O3)(n)FeO+ (n = 2-5) were measured and assigned using calculated harmonic IR spectra from density functional theory (DFT). The substitution of Fe for Al at 3-fold oxygen coordination sites resulted in elongation of metal oxygen bonds without significantly perturbing the Al-O network structure. Unlike Al2FeO4+ (n = 1), valence isomerism was not observed in this study due to a smaller M:O ratio (M = Al, Fe) and decreasing electron affinities with increasing cluster size.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2022)
Article
Chemistry, Multidisciplinary
Jakob S. Kottmann, Abhinav Anand, Alan Aspuru-Guzik
Summary: The study developed computationally affordable and encoding independent gradient evaluation procedures for unitary coupled-cluster type operators applicable on quantum computers, allowing for evaluation of the gradient of an expectation value using four similar expectation values to reduce cost and enabling the construction of differentiable objective functions. Initial applications were illustrated through extended adaptive approaches for electronic ground and excited states.
Article
Optics
Florian A. Bischoff