A Combined Selected Configuration Interaction and Many-Body Treatment of Static and Dynamical Correlation in Oligoacenes

Schriber, Jeffrey B.; Hannon, Kevin P.; Li, Chenyang; Evangelista, Francesco A.

doi:10.1021/acs.jctc.8b00877

Cited by 64 publications

(80 citation statements)

References 104 publications

(225 reference statements)

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“…For instance, adiabatic ST gaps are known to be sensitive to the optimized geometries, which can result in variations on the order of 1-3 kcal/mol. 66 Overall, given the uncertainties due to the treatment of temperature, solvent, and molecular geometries in these acene calculations, ph-AFQMC with single-determinant trial wavefunctions gives satisfactory agreement with both experiments and other highly-accurate electronic structure methods, and moreover can scale with near-perfect parallel efficiency to systems as large as pentacene in a triple-zeta basis, which has 146 electrons and 856 basis functions.…”

Section: Polyacenesmentioning

confidence: 76%

“…This empirical finding is consistent with previous studies of polyacenes using other wavefunction methods which show little basis set dependence. 32,42,66 Our ph-AFQMC calculations utilize the spin-projection technique detailed in Ref. 55.…”

Section: Restricted Hf (Uhf) Restricted Hf (Rhf) and Its Open-shell mentioning

confidence: 99%

“…AFQMC in the cc-pVTZ basis are shown inTable 7, alongside predictions from state-of-the-art ab initio methods and available experimental data. When more than one experimental value is given in Ref 66,. we choose the value that is closest to that shown in Ref 42…”

mentioning

confidence: 99%

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Singlet–Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo

Shee

Arthur

Zhang

et al. 2019

J. Chem. Theory Comput.

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The energy gap between the lowest-lying singlet and triplet states is an important quantity in chemical photocatalysis, with relevant applications ranging from triplet fusion in optical upconversion to the design of organic light-emitting devices. The ab initio prediction of singlet-triplet (ST) gaps is challenging due to the potentially biradical nature of the involved states, combined with the potentially large size of relevant molecules. In this work, we show that phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) can accurately predict ST gaps for chemical systems with singlet states of highly biradical nature, including a set of 13 small molecules and the ortho-, meta-, and para-isomers of benzyne. With respect to gas-phase experiments, ph-AFQMC using CASSCF trial wavefunctions achieves a mean averaged error of ∼1 1 arXiv:1905.13316v1 [physics.chem-ph] 30 May 2019 kcal/mol. Furthermore, we find that in the context of a spin-projection technique, ph-AFQMC using unrestricted single-determinant trial wavefunctions, which can be readily obtained for even very large systems, produces equivalently high accuracy. We proceed to show that this scalable methodology is capable of yielding accurate ST gaps for all linear polyacenes for which experimental measurements exist, i.e. naphthalene, anthracene, tetracene, and pentacene. Our results suggest a protocol for selecting either unrestricted Hartree-Fock or Kohn-Sham orbitals for the single-determinant trial wavefunction, based on the extent of spin-contamination. These findings pave the way for future investigations of specific photochemical processes involving large molecules with substantial biradical character.

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Section: Polyacenesmentioning

confidence: 76%

Section: Restricted Hf (Uhf) Restricted Hf (Rhf) and Its Open-shell mentioning

confidence: 99%

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Singlet–Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo

Shee

Arthur

Zhang

et al. 2019

J. Chem. Theory Comput.

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“…However, it should be noted for completeness that the domain-averaged Fermi hole, [54] used for analysing exchange effects and chemical bonding in the ground state, and a recently proposed analysis of spin correlation densities [55] follow similar ideas. We will show below that this is an immensely powerful tool that provides intuitive insight into intricate excited-state correlation effects.…”

Section: Felix Plasser* [A]mentioning

confidence: 92%

Visualisation of Electronic Excited‐State Correlation in Real Space

Plasser

2019

ChemPhotoChem

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A method for the visualisation of excited-state electron correlation is introduced and shown to address two notorious problems in excited-state electronic structure theory, the analysis of excitonic correlation and the distinction between covalent and ionic wavefunction character. The method operates by representing the excited state in terms of electron and hole quasiparticles, fixing the hole on a fragment of the system and observing the resulting conditional electron density in real space. The application of this approach to oligothiophene, an exemplary conjugated polymer, illuminates excitonic correlation effects of its excited states in unprecedented clarity and detail. A study of naphthalene shows that the distinction between the ionic and covalent states of this molecule, which has so far only been achieved using elaborate valence-bond theory protocols, arises naturally in terms of electron-hole avoidance and enhanced overlap, respectively. More generally, the method is relevant for any excited state that cannot be described by a single electronic configuration.Electronically excited states of molecules form the underpinnings of a wide range of processes of utmost scientific interest, such as light-driven natural processes [1,2] photochemical reactions, [3] signalling and sensing, [4] and the operation of organoelectronic materials. [5,6] Computational photochemistry has become an indispensable part of scientific investigations in these areas through two main tasks, the interpretation of experimental results and the prediction of unknown photophysical properties. Indeed, the predictive power of computational photochemistry has steadily increased over the recent years due to the tremendous effort spent in the development of new methods as well as rapid progress in computer technology. [7][8][9][10][11][12] However, the interpretation of this wealth of computational data can act as a significant impediment in practical work. Therefore, a number of analysis tools have been developed to quantify excited-state properties [13][14][15][16][17] and to visualise the molecular orbitals (MOs) involved and their location in space in a compact and rigorous way. [18][19][20][21][22][23] However, the above-mentioned visualisation tools -and the MO picture itself -break down if the information of interest does not lie in the MOs themselves but in the interaction of different quasidegenerate electronic configurations. Such cases are widespread and two notorious failures of the MO picture relate to excitons in extended systems [24][25][26] and to ionic/ covalent wavefunction character in alternant hydrocarbons. [27,28] The first case is related to the emergence of band structure in large systems, which leads to excited states formed as a superposition of many different electronic configurations whose description requires moving from the MO picture to a representation in terms of correlated electron and hole quasiparticles. [26,[29][30][31] Previous attempts of visualising the ensuing correlated electron-hole distribution ha...

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“…[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] In particular, low-order MRPT methods have been very successful at computing accurate energies of large strongly correlated systems, due to their relatively low computation cost and ability to treat large active spaces with up to ∼ 30 orbitals. [51][52][53][54][55][56][57][58] Despite significant advances, application of conventional MRPT methods to a wider range of prob-lems, such as simulating excited-state or spectroscopic properties, is hindered by a number of limitations. For example, computation of transition intensities in MRPT is not straightforward due to complexity of the underlying response equations.…”

Section: Introductionmentioning

confidence: 99%

Second-Order Multireference Algebraic Diagrammatic Construction Theory for Photoelectron Spectra of Strongly Correlated Systems

Chatterjee

Sokolov

2019

J. Chem. Theory Comput.

116

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We present a second-order formulation of multi-reference algebraic diagrammatic construction theory [Sokolov, A. Yu. J. Chem. Phys. 2018, 149, 204113] for simulating photoelectron spectra of strongly correlated systems (MR-ADC(2)). The MR-ADC(2) method uses second-order multi-reference perturbation theory (MRPT2) to efficiently obtain ionization energies and spectral densities for many photoelectron transitions in a single computation. In contrast to conventional MRPT2 methods, MR-ADC(2) provides information about ionization of electrons in all orbitals (i.e., core and active) and allows to compute transition properties in straightforward and efficient way. Although equations of MR-ADC(2) depend on four-particle reduced density matrices, we demonstrate that computation of these large matrices can be completely avoided without introducing any approximations. The resulting MR-ADC(2) implementation has a lower computational scaling compared to conventional MRPT2 methods. We present results of MR-ADC(2) for photoelectron spectra of small molecules, carbon dimer, and equally-spaced hydrogen chains (H 10 and H 30 ) and outline directions for future developments.

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A Combined Selected Configuration Interaction and Many-Body Treatment of Static and Dynamical Correlation in Oligoacenes

Cited by 64 publications

References 104 publications

Singlet–Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo

Singlet–Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo

Visualisation of Electronic Excited‐State Correlation in Real Space

Second-Order Multireference Algebraic Diagrammatic Construction Theory for Photoelectron Spectra of Strongly Correlated Systems

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