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The Coupled Cluster (CC) method is used to compute the electronic correlation energy in atoms and molecules and often leads to highly accurate results. However, due to its single-reference nature, standard CC in its projected form fails to…

A unitary coupled-cluster (UCC) form for the wavefunction in the variational quantum eigensolver has been suggested as a systematic way to go beyond the mean-field approximation and include electron correlation in solving quantum chemistry…

Quantum Physics · Physics 2018-09-12 Ilya G. Ryabinkin , Tzu-Ching Yen , Scott N. Genin , Artur F. Izmaylov

Many quantum algorithms rely on a quality initial state for optimal performance. Preparing an initial state for specific applications can considerably reduce the cost of probabilistic algorithms such as the well studied quantum phase…

Quantum Physics · Physics 2024-12-10 Alexandre Fleury , James Brown , Erika Lloyd , Maritza Hernandez , Isaac H. Kim

We present a quantum-classical hybrid algorithm that simulates electronic structures of periodic systems such as ground states and quasiparticle band structures. By extending the unitary coupled cluster (UCC) theory to describe crystals in…

Quantum Physics · Physics 2022-02-16 Nobuyuki Yoshioka , Takeshi Sato , Yuya O. Nakagawa , Yu-ya Ohnishi , Wataru Mizukami

Immense interest in quantum computing has prompted development of electronic structure methods that are suitable for quantum hardware. However, the slow pace at which quantum hardware progresses, forces researchers to implement their ideas…

Quantum Physics · Physics 2025-02-26 Ilya G. Ryabinkin , Seyyed Mehdi Hosseini Jenab , Scott N. Genin

Unitary coupled cluster (UCC), originally developed as a variational alternative to the popular traditional coupled cluster method, has seen a resurgence as a functional form for use on quantum computers. However, the number of excitors…

Chemical Physics · Physics 2021-01-07 Maria-Andreea Filip , Alex J. W. Thom

The unitary coupled cluster (UCC) approximation is one of the more promising wave-function ans\"atze for electronic structure calculations on quantum computers via the variational quantum eigensolver algorithm. However, for large systems…

Quantum Physics · Physics 2021-09-30 Jia Chen , Hai-Ping Cheng , James K. Freericks

The variational quantum eigensolver (VQE) algorithm combines the ability of quantum computers to efficiently compute expectation values with a classical optimization routine in order to approximate ground state energies of quantum systems.…

The recently introduced coupled cluster (CC) downfolding techniques for reducing the dimensionality of quantum many-body problems recast the CC formalism in the form of the renormalization procedure allowing, for the construction of…

Quantum Physics · Physics 2021-11-08 Nicholas P. Bauman , Karol Kowalski

Shallow, CNOT-efficient quantum circuits are crucial for performing accurate computational chemistry simulations on current noisy quantum hardware. Here, we explore the usefulness of non-iterative energy corrections, based on the method of…

Chemical Physics · Physics 2023-05-03 Ilias Magoulas , Francesco A. Evangelista

We introduce a unitary coupled-cluster (UCC) ansatz termed $k$-UpCCGSD that is based on a family of sparse generalized doubles (D) operators which provides an affordable and systematically improvable unitary coupled-cluster wavefunction…

Quantum Physics · Physics 2019-01-07 Joonho Lee , William J. Huggins , Martin Head-Gordon , K. Birgitta Whaley

In truncated coupled-cluster (CC) theories, non-variational and/or generally complex ground-state energies can occur. This is due to the non-Hermitian nature of the similarity transformed Hamiltonian matrix in combination with CC…

Chemical Physics · Physics 2023-09-22 Tanner Culpitt , Erik I. Tellgren , Fabijan Pavosevic

The coupled cluster method (CCM) is a method of quantum many-body theory that may provide accurate results for the ground-state properties of lattice quantum spin systems even in the presence of strong frustration and for lattices of…

Strongly Correlated Electrons · Physics 2009-11-11 D. J. J. Farnell , J. Schulenburg , J. Richter , K. A. Gernoth

Quantum chemistry calculations of large, strongly correlated systems are typically limited by the computation cost that scales exponentially with the size of the system. Quantum algorithms, designed specifically for quantum computers, can…

Multicomponent systems are defined as chemical systems that require a quantum mechanical description of two or more different types of particles. Non-Born-Oppenheimer electron-nuclear interactions in molecules, electron-hole interactions in…

Chemical Physics · Physics 2015-10-21 Benjamin H. Ellis , Somil Aggarwal , Arindam Chakraborty

Quantum computing and quantum Monte Carlo (QMC) are respectively the state-of-the-art quantum and classical computing methods for understanding many-body quantum systems. Here, we propose a hybrid quantum-classical algorithm that integrates…

Quantum Physics · Physics 2025-11-17 Yukun Zhang , Yifei Huang , Jinzhao Sun , Dingshun Lv , Xiao Yuan

We recently proposed a novel approach to converging electronic energies equivalent to high-level coupled-cluster (CC) computations by combining the deterministic CC($P$;$Q$) formalism with the stochastic configuration interaction (CI) and…

Chemical Physics · Physics 2021-03-23 J. Emiliano Deustua , Jun Shen , Piotr Piecuch

A major difficulty in quantum simulation is the adequate treatment of a large collection of entangled particles, synonymous with electron correlation in electronic structure theory, with coupled cluster (CC) theory being the leading…

Chemical Physics · Physics 2024-06-06 Zachary W. Windom , Daniel Claudino , Rodney J. Bartlett

We introduce a multicomponent unitary coupled cluster framework for quantum simulations of molecular systems that incorporate both electronic and nuclear quantum effects beyond the Born-Oppenheimer approximation. Using the…

The development of multireference coupled cluster (MRCC) techniques has remained an open area of study in electronic structure theory for decades due to the inherent complexity of expressing a multi-configurational wavefunction in the…

Chemical Physics · Physics 2023-05-24 Maria-Andreea Filip , Alex J. W. Thom
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