Internally contracted multireference coupled-cluster theory in a multistate framework

Aoto, Yuri Alexandre; Köhn, Andreas

doi:10.1063/1.4941604

Cited by 32 publications

(30 citation statements)

References 42 publications

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“…Another possibility to access excited states is the multistate version of the ic-MRCC method, which has been presented recently by Aoto and Köhn. 251 Not too much experience is available yet, but it is hoped that in this way it will be possible to describe state crossing (also with the ground state). Promising results have been presented for LiF and BeF.…”

Section: Multireference Coupled Cluster Methodsmentioning

confidence: 99%

“…Promising results have been presented for LiF and BeF. 251 The relation of pIC-MRCC to EOM-CC led to its straightforward generalization for multiple states. In the so-called MR-EOMCC method of Nooijen and coworkers, [252][253][254] instead of diagonalizing H in the MRCIS space as in pIC-MRCC, the space is now extended by the inclusion of up to double excitations into the active space.…”

Section: Multireference Coupled Cluster Methodsmentioning

confidence: 99%

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Multireference Approaches for Excited States of Molecules

et al. 2018

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Understanding the properties of electronically excited states is a challenging task that becomes increasingly important for numerous applications in chemistry, molecular physics, molecular biology, and materials science. A substantial impact is exerted by the fascinating progress in time-resolved spectroscopy, which leads to a strongly growing demand for theoretical methods to describe the characteristic features of excited states accurately. Whereas for electronic ground state problems of stable molecules the quantum chemical methodology is now so well developed that informed nonexperts can use it efficiently, the situation is entirely different concerning the investigation of excited states. This review is devoted to a specific class of approaches, usually denoted as multireference (MR) methods, the generality of which is needed for solving many spectroscopic or photodynamical problems. However, the understanding and proper application of these MR methods is often found to be difficult due to their complexity and their computational cost. The purpose of this review is to provide an overview of the most important facts about the different theoretical approaches available and to present by means of a collection of characteristic examples useful information, which can guide the reader in performing their own applications.

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Section: Multireference Coupled Cluster Methodsmentioning

confidence: 99%

Section: Multireference Coupled Cluster Methodsmentioning

confidence: 99%

Multireference Approaches for Excited States of Molecules

et al. 2018

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“…Relaxing the reference coefficients is in fact one of the main reasons for the particular accuracy of the resulting method and it has been shown that it thus unifies state-specific and multistate coupled-cluster theories. 141 The success of the method comes at a price of high complexity of the underlying equations, in particular due to the non-commutativity of the cluster operator manifold. 138 The current Molpro implementation still relies on a symbolic code (called GeCCo) that is generated by the automatized evaluation of the underlying secondquantized operator algebra.…”

Section: Internally Contracted Multireference Coupled-clustermentioning

confidence: 99%

The Molpro quantum chemistry package

Werner

Knowles

Manby

et al. 2020

The Journal of Chemical Physics

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994

737

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Molpro is a general purpose quantum chemistry software package with a long development history. It was originally focused on accurate wavefunction calculations for small molecules but now has many additional distinctive capabilities that include, inter alia, local correlation approximations combined with explicit correlation, highly efficient implementations of single-reference correlation methods, robust and efficient multireference methods for large molecules, projection embedding, and anharmonic vibrational spectra. In addition to conventional input-file specification of calculations, Molpro calculations can now be specified and analyzed via a new graphical user interface and through a Python framework.

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“…This unphysical behavior inherent of SA-CASSCF must be cured a posteriori by multistate variants of MRPT 4,85−87 or MRCC. 88…”

Section: Introductionmentioning

confidence: 99%

Benchmarks for Electronically Excited States with CASSCF Methods

Helmich‐Paris

2019

J. Chem. Theory Comput.

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The accuracy of three different complete active space (CAS) self-consistent field (CASSCF) methods is investigated for the electronically excited-state benchmark set of SchreiberM.SchreiberM.18397056J. Chem. Phys.2008128134110. Comparison of the CASSCF linear response (LR) methods MC-RPA and MC-TDA and the state-averaged (SA) CASSCF method is made for 122 singlet excitation energies and 69 oscillator strengths. Of all CASSCF methods, when considering the complete test set, MC-RPA performs best for both excitation energies and oscillator strengths with a mean absolute error (MAE) of 0.74 eV and 51%, respectively. MC-TDA and SA-CASSCF show a similar accuracy for the excitation energies with a MAE of ∼1 eV with respect to more accurate coupled cluster (CC3) excitation energies. The opposite trend is observed for the subset of n → π* excitation energies for which SA-CASSCF exhibits the least deviations (MAE 0.65 eV). By looking at s-tetrazine in more detail, we conclude that better performance for the n → π* SA-CASSCF excitation energies can be attributed to a fortunate error compensation. For oscillator strengths, SA-CASSCF performs worst for the complete test set (MAE 100%) as well as for the subsets of n → π* (MAE 192%) and π → π* excitations (MAE 84.9%). In general, CASSCF gives the worst performance for excitation energies of all excited-state ab initio methods considered so far due to lacking the major part of dynamic electron correlation, though MC-RPA and TD-DFT (BP86) show similar performance. Among all LR-type methods, LR-CASSCF oscillator strengths are the ones with the least accuracy for the same reason. As state-specific orbital relaxation effects are accounted for in LR-CASSCF, oscillator strengths are significantly more accurate than those of MS-CASPT2. Our findings should encourage further developments of response theory-based multireference methods with higher accuracy and feasibility.

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Internally contracted multireference coupled-cluster theory in a multistate framework

Cited by 32 publications

References 42 publications

Multireference Approaches for Excited States of Molecules

Multireference Approaches for Excited States of Molecules

The Molpro quantum chemistry package

Benchmarks for Electronically Excited States with CASSCF Methods

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