Low-Lying ππ* States of Heteroaromatic Molecules: A Challenge for Excited State Methods

Prlj, Antonio; Sandoval‐Salinas, María Eugenia; Casanova, David; Jacquemin, Denis; Corminbœuf, Clémence

doi:10.1021/acs.jctc.6b00245

Cited by 66 publications

(98 citation statements)

References 79 publications

(162 reference statements)

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“…Excitations that can only be represented by transitions between multiple orbital pairs that have no common orbitals are unlikely to be well described on account of their natively multiconfigurational nature. A rather well-known example of the latter are the L b dark states in polyaromatic compounds 75. 4 Applications4.1 Comparison of SGM to MOM and IMOM…”

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confidence: 99%

Excited State Orbital Optimization via Minimizing the Square of the Gradient: General Approach and Application to Singly and Doubly Excited States via Density Functional Theory

Hait

Head‐Gordon

2020

J. Chem. Theory Comput.

164

297

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We present a general approach to converge excited state solutions to any quantum chemistry orbital optimization process, without the risk of variational collapse.The resulting Square Gradient Minimization (SGM) approach only requires analytic energy/Lagrangian orbital gradients and merely costs 3 times as much as ground state orbital optimization (per iteration), when implemented via a finite difference approach.SGM is applied to both single determinant ∆SCF and spin-purified Restricted Open-Shell Kohn-Sham (ROKS) approaches to study the accuracy of orbital optimized DFT excited states. It is found that SGM can converge challenging states where the Maximum Overlap Method (MOM) or analogues either collapse to the ground state or fail to converge. We also report that ∆SCF/ROKS predict highly accurate excitation 1 arXiv:1911.04709v1 [physics.chem-ph] 12 Nov 2019 energies for doubly excited states (which are inaccessible via TDDFT). Singly excited states obtained via ROKS are also found to be quite accurate, especially for Rydberg states that frustrate (semi)local TDDFT. Our results suggest that orbital optimized excited state DFT methods can be used to push past the limitations of TDDFT to doubly excited, charge-transfer or Rydberg states, making them a useful tool for the practical quantum chemist's toolbox for studying excited states in large systems. IntroductionAccurate quantum chemical methods for modeling electronic excited states are essential for gaining insight into the photophysics and photochemistry of molecules and materials. The most widely used technique for excited state calculations at present is time dependent density functional theory (TDDFT), 1-5 on account of its relatively low computational complexity (O(N 2−3 ), where N is the molecule size) and reasonable accuracy for many problems. 6,7 TDDFT excited states are computed via determining the linear response of a ground state DFT solution to time-dependent external electric fields, 5 permitting simultaneous modeling of multiple excited states. In principle, TDDFT is formally exact 1 when the exact exchangecorrelation (xc) ground state functional is employed, although lack of that functional, and the need for the widely used adiabatic local density approximation 3-5 (ALDA) prevents this from being the case in practice. ALDA in fact restricts utility of TDDFT to single excitations out of the reference alone, with large errors arising whenever the target excited state has significant double (or higher) excitation character. 8-11 Furthermore, TDDFT is known to systematically underestimate excitation energies for charge-transfer 5,12-14 and Rydberg 8,15 states, and yields qualitatively erroneous potential energy surfaces along single bond dissociation coordinates. 16 These effects originally stem from errors in the ground state DFT solution like delocalization error 17,18 or spin symmetry breaking, 19,20 but the linear response protocol augments these deficiencies in the reference to catastrophic levels in excited states, on account of insufficient or...

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confidence: 99%

Excited State Orbital Optimization via Minimizing the Square of the Gradient: General Approach and Application to Singly and Doubly Excited States via Density Functional Theory

Hait

Head‐Gordon

2020

J. Chem. Theory Comput.

164

297

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“…[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. [48][49][50][51] It is the purpose of this Communication to introduce a generally applicable and intuitive method for the analysis of excited-state correlation effects and to exemplify its power in the above-mentioned cases of exciton correlation and ionic/ covalent wavefunction character. The second case derives from quasidegeneracies induced by approximate symmetries [41] and plays a role even for common smaller molecules such as butadiene, benzene, and naphthalene.…”

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confidence: 99%

“…[27,42] This distinction has existed since the early days of molecular quantum mechanics [41] but the quantification of covalent and ionic character is still quite cumbersome requiring specialised VB protocols [43] and has remained an active research topic. [48][49][50][51] It is the purpose of this Communication to introduce a generally applicable and intuitive method for the analysis of excited-state correlation effects and to exemplify its power in the above-mentioned cases of exciton correlation and ionic/ covalent wavefunction character. [48][49][50][51] It is the purpose of this Communication to introduce a generally applicable and intuitive method for the analysis of excited-state correlation effects and to exemplify its power in the above-mentioned cases of exciton correlation and ionic/ covalent wavefunction character.…”

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confidence: 99%

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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“…Characterizing aromatic exciplexes involves a number of challenges for electronic structure methods. Several methods fail to give the correct ordering for the valence π → π * excitations of linear acene monomers . Calculating binding energies presents further difficulties.…”

Section: Introductionmentioning

confidence: 99%

“…π * excitations of linear acene monomers. [11][12][13][14] Calculating binding energies presents further difficulties. If molecules P and Q have a minimum-energy separation r 0 in the excited state, the binding energy E B is defined here as the difference between the energy of the molecules at r 0 and at infinite separation, with attractive interaction energies defined as positive for convenience:…”

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confidence: 99%

Multireference exciplex binding energies: Basis set convergence and error

Krueger

Blanquart

2018

Int J of Quantum Chemistry

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In multichromophore systems, characterization of electronic structure requires characterization of exciplexes, electron‐hole pairs delocalized over multiple molecules. Computing exciplex binding energy requires an accurate description of both the noncovalent interactions between the chromophores and their excited electronic states. The critical role of basis set selection for accurate description of noncovalent interactions is well known, but for some of the most accurate excited‐state methods, basis set dependence is incompletely understood. In this work, the impact of basis set size and diffuseness on CASSCF/NEVPT2 binding energies is determined for three systems in their lowest singlet excited states: the benzene excimer, the cis‐butadiene‐benzene exciplex, and the benzene‐naphthalene exciplex. We demonstrate that excellent CBS binding energies may be obtained using the moderately‐sized jun‐cc‐pV(D + d)Z and jun‐cc‐pV(T + d)Z basis sets and a simple N−3 model. Repeating this procedure with the N = 3, 4 basis sets from the most diffuse basis set family applied to each system yields a binding energy of 56.6 ± 1.2 kJ/mol for the benzene excimer and binding energies of 11.1 ± 0.5 kJ/mol and 19.2 ± 1.7 kJ/mol for the cis‐butadiene‐benzene exciplex and the benzene‐naphthalene exciplex, respectively.

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Low-Lying ππ* States of Heteroaromatic Molecules: A Challenge for Excited State Methods

Cited by 66 publications

References 79 publications

Excited State Orbital Optimization via Minimizing the Square of the Gradient: General Approach and Application to Singly and Doubly Excited States via Density Functional Theory

Excited State Orbital Optimization via Minimizing the Square of the Gradient: General Approach and Application to Singly and Doubly Excited States via Density Functional Theory

Visualisation of Electronic Excited‐State Correlation in Real Space

Multireference exciplex binding energies: Basis set convergence and error

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