A simple approach to the state-specific MR-CC using the intermediate Hamiltonian formalism

Giner, Emmanuel; David, Grégoire; Scemama, Anthony; Malrieu, Jean‐Paul

doi:10.1063/1.4940781

Cited by 20 publications

(24 citation statements)

References 58 publications

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“…Dissociation curves. Difference with respect to the Full-CI energy using the MR-CCSD method presented in ref15 and with the MR-CCSD method proposed in this work, as well as the CAS-SD and the dressed CAS-SD.…”

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confidence: 96%

Alternative definition of excitation amplitudes in multi-reference state-specific coupled cluster

Garniron

Giner

Malrieu

et al. 2017

The Journal of Chemical Physics

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A central difficulty of state-specific Multi-Reference Coupled Cluster (MR-CC) in the multi-exponential Jeziorski-Monkhorst formalism concerns the definition of the amplitudes of the single and double excitation operators appearing in the exponential wave operators. If the reference space is a complete active space (CAS), the number of these amplitudes is larger than the number of singly and doubly excited determinants on which one may project the eigenequation, and one must impose additional conditions. The present work first defines a state-specific reference-independent operator T∼^ which acting on the CAS component of the wave function |Ψ⟩ maximizes the overlap between (1+T∼^)|Ψ⟩ and the eigenvector of the CAS-SD (Singles and Doubles) Configuration Interaction (CI) matrix |Ψ⟩. This operator may be used to generate approximate coefficients of the triples and quadruples, and a dressing of the CAS-SD CI matrix, according to the intermediate Hamiltonian formalism. The process may be iterated to convergence. As a refinement towards a strict coupled cluster formalism, one may exploit reference-independent amplitudes provided by (1+T∼^)|Ψ⟩ to define a reference-dependent operator T^ by fitting the eigenvector of the (dressed) CAS-SD CI matrix. The two variants, which are internally uncontracted, give rather similar results. The new MR-CC version has been tested on the ground state potential energy curves of 6 molecules (up to triple-bond breaking) and two excited states. The non-parallelism error with respect to the full-CI curves is of the order of 1 mE.

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confidence: 96%

Alternative definition of excitation amplitudes in multi-reference state-specific coupled cluster

Garniron

Giner

Malrieu

et al. 2017

The Journal of Chemical Physics

Self Cite

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“…To treat even larger systems, the increase of the number of determinants in the CIPSI expansion must be kept under control. Instead of targeting the near full CI limit, simpler models can be used in the spirit of what is done in MRCC approaches [95] or by defining effective Hamiltonians in the reference space modelling the effect of the external space (so-called internally decontracted approaches).…”

Section: Summary and Some Perspectivesmentioning

confidence: 99%

“…We emphasize that the idea of selecting determinants is not limited to the entire space of determinants but can be used to make CI expansion to converge in a subset of determinants chosen a priori. For example, efficient and accurate selected CASCI, CISD, or even MRCC [95] calculations can be performed. Note that going beyond CASCI and implementing a selected CASSCF approach (CASCI with optimization of molecular orbitals)…”

Section: Summary and Some Perspectivesmentioning

confidence: 99%

Using CIPSI Nodes in Diffusion Monte Carlo

Caffarel

Applencourt

Giner

et al. 2016

ACS Symposium Series

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Several aspects of the recently proposed DMC-CIPSI approach consisting in using selected Configuration Interaction (SCI) approaches such as CIPSI (Configuration Interaction using a Perturbative Selection done Iteratively) to build accurate nodes for diffusion Monte Carlo (DMC) calculations are presented and discussed. The main ideas are illustrated with a number of calculations for diatomics molecules and for the benchmark G1 set.

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“…Multiple external plugins were developed by the authors. For instance, one can nd a multi-reference coupled cluster program, 116,132 interfaces with the quantum Monte Carlo programs QMC=Chem, 133 QMCPack 134 and CHAMP, 135 an implementation of the shi ed-Bk method, 45 a program combining CIPSI with RSDFT, 136 a four-component relativistic RSDFT code, 137 and many others.…”

Section: The Plugin Systemmentioning

confidence: 99%

Quantum Package 2.0: An Open-Source Determinant-Driven Suite of Programs

Garniron¹,

Applencourt²,

Gasperich³

et al. 2019

Preprint

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<div> <div> <div> <p> </p><div> <div> <div> <p>Quantum Package is an open-source programming environment for quantum chemistry specially designed for wave function methods. Its main goal is the development of determinant-driven selected configuration interaction (sCI) methods and multi-reference second-order perturbation theory (PT2). The determinant-driven framework allows the programmer to include any arbitrary set of determinants in the reference space, hence providing greater method- ological freedoms. The sCI method implemented in Quantum Package is based on the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) algorithm which complements the variational sCI energy with a PT2 correction. Additional external plugins have been recently added to perform calculations with multireference coupled cluster theory and range-separated density-functional theory. All the programs are developed with the IRPF90 code generator, which simplifies collaborative work and the development of new features. Quantum Package strives to allow easy implementation and experimentation of new methods, while making parallel computation as simple and efficient as possible on modern supercomputer architectures. Currently, the code enables, routinely, to realize runs on roughly 2 000 CPU cores, with tens of millions of determinants in the reference space. Moreover, we have been able to push up to 12 288 cores in order to test its parallel efficiency. In the present manuscript, we also introduce some key new developments: i) a renormalized second-order perturbative correction for efficient extrapolation to the full CI limit, and ii) a stochastic version of the CIPSI selection performed simultaneously to the PT2 calculation at no extra cost. </p> </div> </div> </div> </div> </div> </div>

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A simple approach to the state-specific MR-CC using the intermediate Hamiltonian formalism

Cited by 20 publications

References 58 publications

Alternative definition of excitation amplitudes in multi-reference state-specific coupled cluster

Alternative definition of excitation amplitudes in multi-reference state-specific coupled cluster

Using CIPSI Nodes in Diffusion Monte Carlo

Quantum Package 2.0: An Open-Source Determinant-Driven Suite of Programs

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