arXiv subjects

Denis Jacquemin

Publications and source records attributed to Denis Jacquemin.

At least 37 records · Page 2Linked to original sources

arXiv2021

Reference Energies for Intramolecular Charge-Transfer Excitations

In the aim of completing our previous efforts devoted to local and Rydberg transitions in organic compounds, we provide a series of highly-accurate vertical transition energies for intramolecular charge-transfer transitions occurring in ($π$-conjugated) molecular compounds. To this end we apply a composite protocol consisting of linear-response CCSDT excitation energies determined with Dunning's double-$ζ$ basis set corrected by CC3/CCSDT-3 energies obtained with the corresponding triple-$ζ$ basis. Further basis set corrections (up to \emph{aug}-cc-pVQZ) are obtained at the CCSD and CC2 level. We report 30 transitions obtained in 17 compounds. These reference values are then used to benchmark a series of wave function (CIS(D), SOPPA, RPA(D), EOM-MP2, CC2, CCSD, CCSD(T)(a)*, CCSDR(3), CCSDT-3, CC3, ADC(2), ADC(3), and ADC(2.5)), the Green's function-based Bethe-Salpeter equation (BSE) formalism performed on top of the partially self-consistent ev$GW$ scheme considering two different starting points (BSE/ev$GW$@HF and BSE/ev$GW$@PBE0), and TD-DFT combined with several exchange-correlation functionals (B3LYP, PBE0, M06-2X, CAM-B3LYP, LC-$ω$HPBE, $ω$B97X, $ω$B97X-D, and M11).

physics.chem-ph↗

arXiv2021

Benchmarking TD-DFT and Wave Function Methods for Oscillator Strengths and Excited-State Dipole Moments

Using a set of oscillator strengths and excited-state dipole moments of near full configuration interaction (FCI) quality determined for small compounds, we benchmark the performances of several single-reference wave function methods (CC2, CCSD, CC3, CCSDT, ADC(2), and ADC(3/2)) and time-dependent density-functional theory (TD-DFT) with various functionals (B3LYP, PBE0, M06-2X, CAM-B3LYP, and $ω$B97X-D). We consider the impact of various gauges (length, velocity, and mixed) and formalisms: equation of motion (EOM) \emph{vs} linear response (LR), relaxed \emph{vs} unrelaxed orbitals, etc. Beyond the expected accuracy improvements and a neat decrease of formalism sensitivy when using higher-order wave function methods, the present contribution shows that, for both ADC(2) and CC2, the choice of gauge impacts more significantly the magnitude of the oscillator strengths than the choice of formalism, and that CCSD yields a notable improvement on this transition property as compared to CC2. For the excited-state dipole moments, switching on orbital relaxation appreciably improves the accuracy of both ADC(2) and CC2, but has a rather small effect at the CCSD level. Going from ground to excited states, the typical errors on dipole moments for a given method tend to roughly triple. Interestingly, the ADC(3/2) oscillator strengths and dipoles are significantly more accurate than their ADC(2) counterparts, whereas the two models do deliver rather similar absolute errors for transition energies. Concerning TD-DFT, one finds: i) a rather negligible impact of the gauge on oscillator strengths for all tested functionals (except for M06-2X); ii) deviations of ca.~0.10 D on ground-state dipoles for all functionals; iii) the better overall performance of CAM-B3LYP for the two considered excited-state properties.

physics.chem-ph↗

arXiv2021

QUESTDB: a database of highly-accurate excitation energies for the electronic structure community

We describe our efforts of the past few years to create a large set of more than 500 highly-accurate vertical excitation energies of various natures ($π\to π^*$, $n \to π^*$, double excitation, Rydberg, singlet, doublet, triplet, etc) in small- and medium-sized molecules. These values have been obtained using an incremental strategy which consists in combining high-order coupled cluster and selected configuration interaction calculations using increasingly large diffuse basis sets in order to reach high accuracy. One of the key aspect of the so-called QUEST database of vertical excitations is that it does not rely on any experimental values, avoiding potential biases inherently linked to experiments and facilitating theoretical cross comparisons. Following this composite protocol, we have been able to produce theoretical best estimate (TBEs) with the aug-cc-pVTZ basis set for each of these transitions, as well as basis set corrected TBEs (i.e., near the complete basis set limit) for some of them. The TBEs/aug-cc-pVTZ have been employed to benchmark a large number of (lower-order) wave function methods such as CIS(D), ADC(2), CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, ADC(3), CC3, NEVPT2, and others (including spin-scaled variants). In order to gather the huge amount of data produced during the QUEST project, we have created a website [https://lcpq.github.io/QUESTDB_website] where one can easily test and compare the accuracy of a given method with respect to various variables such as the molecule size or its family, the nature of the excited states, the type of basis set, etc. We hope that the present review will provide a useful summary of our effort so far and foster new developments around excited-state methods.

physics.chem-ph↗

arXiv2020

A Mountaineering Strategy to Excited States: Highly-Accurate Oscillator Strengths and Dipole Moments of Small Molecules

This work presents a series of highly-accurate excited-state properties obtained using high-order coupled-cluster (CC) calculations performed with a series of diffuse containing basis sets, as well as extensive comparisons with experimental values. Indeed, we have computed both the main ground-to-excited transition property, the oscillator strength, as well as the ground- and excited-state dipole moments, considering {thirteen} small molecules (hydridoboron, hydrogen chloride, water, hydrogen sulfide, boron fluoride, carbon monoxide, dinitrogen, ethylene, formaldehyde, thioformaldehyde, nitroxyl, {fluorocarbene}, and silylidene). We systematically include corrections up to the quintuple (CCSDTQP) in the CC expansion and extrapolate to the complete basis set limit. When comparisons with experimental measurements are possible, that is, when a number of consistent experimental data can be found, theory typically provides values falling within the experimental error bar for the excited-state properties. Besides completing our previous studies focussed on transition energies (\textit{J.~Chem.~Theory Comput.} \textbf{14} (2018) 4360--4379, \textit{ibid.}~\textbf{15} (2019) 1939--1956, \textit{ibid.}~\textbf{16} (2020) 1711--1741, and \textit{ibid.}~\textbf{16} (2020) 3720--3736), this work also provides ultra-accurate dipoles and oscillator strengths that could be employed for future theoretical benchmarks.

physics.chem-ph↗

arXiv2020

The Bethe-Salpeter Equation Formalism: From Physics to Chemistry

The Bethe-Salpeter equation (BSE) formalism is steadily asserting itself as a new efficient and accurate tool in the ensemble of computational methods available to chemists in order to predict optical excitations in molecular systems. In particular, the combination of the so-called $GW$ approximation, giving access to reliable ionization energies and electron affinities, and the BSE formalism, able to model UV/Vis spectra, has shown to provide accurate singlet excitation energies with a typical error of $0.1$--$0.3$ eV. With a similar computational cost as time-dependent density-functional theory (TD-DFT), BSE is able to provide an accuracy on par with the most accurate global and range-separated hybrid functionals without the unsettling choice of the exchange-correlation functional, resolving further known issues (\textit{e.g.}, charge-transfer excitations). In this \textit{Perspective} article, we provide a historical overview of BSE, with a particular focus on its condensed-matter roots. We also propose a critical review of its strengths and weaknesses in different chemical situations.

physics.chem-ph↗

arXiv2020

Pros and Cons of the Bethe-Salpeter Formalism for Ground-State Energies

The combination of the many-body Green's function $GW$ approximation and the Bethe-Salpeter equation (BSE) formalism has shown to be a promising alternative to time-dependent density-functional theory (TD-DFT) for computing vertical transition energies and oscillator strengths in molecular systems. The BSE formalism can also be employed to compute ground-state correlation energies thanks to the adiabatic-connection fluctuation-dissipation theorem (ACFDT). Here, we study the topology of the ground-state potential energy surfaces (PES) of several diatomic molecules near their equilibrium bond length. Thanks to comparisons with state-of-art computational approaches (CC3), we show that ACFDT@BSE is surprisingly accurate, and can even compete with lower-order coupled cluster methods (CC2 and CCSD) in terms of total energies and equilibrium bond distances for the considered systems. However, we sometimes observe unphysical irregularities on the ground-state PES in relation with difficulties in the identification of a few $GW$ quasiparticle energies.

physics.chem-ph↗

arXiv2020

A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Exotic Molecules and Radicals

Aiming at completing the sets of FCI-quality transition energies that we recently developed (\textit{J.~Chem.~Theory Comput.} \textbf{14} (2018) 4360--4379, \textit{ibid.}~\textbf{15} (2019) 1939--1956, and \textit{ibid.}~\textbf{16} (2020) 1711--1741), we provide, in the present contribution, ultra-accurate vertical excitation energies for a series of "exotic" closed-shell molecules containing F, Cl, P, and Si atoms and small radicals, such as CON and its variants, that were not considered to date in such investigations. This represents a total of 81 high-quality transitions obtained with a series of diffuse-containing basis sets of various sizes. For the exotic compounds, these transitions are used to perform benchmarks with a vast array of lower-level models, $\textit{i.e.}$ CIS(D), EOM-MP2, (SOS/SCS)-CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, (SOS-)ADC(2), and ADC(3). Additional comparisons are made with literature data. For the open-shell compounds, we have compared the performances of both the unrestricted and restricted open-shell CCSD and CC3 formalisms.

physics.chem-ph↗

arXiv2020

A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Medium Size Molecules

Following our previous work focussing on compounds containing up to 3 non-hydrogen atoms [\emph{J. Chem. Theory Comput.} {\bfseries 14} (2018) 4360--4379], we present here highly-accurate vertical transition energies obtained for 27 molecules encompassing 4, 5, and 6 non-hydrogen atoms. To obtain these energies, we use equation-of-motion coupled cluster theory up to the highest technically possible excitation order for these systems (CC3, EOM-CCSDT, and EOM-CCSDTQ), selected configuration interaction (SCI) calculations (with tens of millions of determinants in the reference space), as well as the multiconfigurational $n$-electron valence state perturbation theory (NEVPT2) method. All these approaches are applied in combination with diffuse-containing atomic basis sets. For all transitions, we report at least CC3/\emph{aug}-cc-pVQZ vertical excitation energies as well as CC3/\emph{aug}-cc-pVTZ oscillator strengths for each dipole-allowed transition. We show that CC3 almost systematically delivers transition energies in agreement with higher-level methods with a typical deviation of $\pm 0.04$ eV, except for transitions with a dominant double excitation character where the error is much larger. The present contribution gathers a large, diverse and accurate set of more than 200 highly-accurate transition energies for states of various natures (valence, Rydberg, singlet, triplet, $n \rightarrow π^*$, $π\rightarrow π^*$, \ldots). We use this series of theoretical best estimates to benchmark a series of popular methods for excited state calculations: CIS(D), ADC(2), CC2, STEOM-CCSD, EOM-CCSD, CCSDR(3), CCSDT-3, CC3, as well as NEVPT2. The results of these benchmarks are compared to the available literature data.

physics.chem-ph↗

arXiv2020

The Quest For Highly Accurate Excitation Energies: A Computational Perspective

We provide an overview of the successive steps that made possible to obtain increasingly accurate excitation energies with computational chemistry tools, eventually leading to chemically accurate vertical transition energies for small- and medium-size molecules. First, we describe the evolution of \textit{ab initio} methods employed to define benchmark values, with originally Roos' CASPT2 method, then the CC3 method as in the renowned Thiel set, and more recently the resurgence of selected configuration interaction methods. The latter method has been able to deliver consistently, for both single and double excitations, highly accurate excitation energies for small molecules, as well as medium-size molecules with compact basis sets. Second, we describe how these high-level methods and the creation of representative benchmark sets of excitation energies have allowed to assess fairly and accurately the performance of computationally lighter methods. We conclude by discussing the future theoretical and technological developments in the field.

physics.chem-ph↗

arXiv2019

Is ADC(3) as Accurate as CC3 for Valence and Rydberg Transition Energies?

The search for new \emph{ab initio} models rapidly delivering accurate excited state energies and properties is one of the most active research lines of theoretical chemistry. Along with these methodological developments, the performances of known methods are constantly reassessed thanks to the emergence of new benchmark values. In this Letter, we show that, in contrast to previous claims, the third-order algebraic diagrammatic construction, ADC(3), does not yield transition energies of the same quality as the third-order coupled cluster method, CC3. There is indeed a significant difference in terms of accuracy between the two approaches, as we clearly and unambiguously demonstrate here thanks to extensive comparisons with several hundreds high-quality vertical transition energies obtained with FCI, CCSDTQ, and CCSDT. Direct comparisons with experimental 0-0 energies of small- and medium-size organic molecules support the same conclusion, which holds for both valence and Rydberg transitions, as well as singlet and triplet states. In regards of these results, we introduce a composite approach that we named ADC(2.5) which consists in averaging the ADC(2) and ADC(3) excitation energies. Although ADC(2.5) does not match the CC3 accuracy, it significantly improves the ADC(3) results, especially for vertical energies. We hope that the present contribution will stimulate further developments and, in particular, improvements of the ADC-type methods which have the indisputable advantage of being computationally lighter than their equivalent-order CC variants.

physics.chem-ph↗

arXiv2019

Influence of Pseudopotentials on Excitation Energies From Selected Configuration Interaction and Diffusion Monte Carlo

Due to their diverse nature, the faithful description of excited states within electronic structure theory methods remains one of the grand challenges of modern theoretical chemistry. Quantum Monte Carlo (QMC) methods have been applied very successfully to ground state properties but still remain generally less effective than other non-stochastic methods for electronically excited states. Nonetheless, we have recently reported accurate excitation energies for small organic molecules at the fixed-node diffusion Monte Carlo (FN-DMC) within a Jastrow-free QMC protocol relying on a deterministic and systematic construction of nodal surfaces using the selected configuration interaction (sCI) algorithm known as CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively). Albeit highly accurate, these all-electron calculations are computationally expensive due to the presence of core electrons. One very popular approach to remove these chemically-inert electrons from the QMC simulation is to introduce pseudopotentials (also known as effective core potentials). Taking the water molecule as an example, we investigate the influence of Burkatzki-Filippi-Dolg (BFD) pseudopotentials and their associated basis sets on vertical excitation energies obtained with sCI and FN-DMC methods. Although these pseudopotentials are known to be relatively safe for ground state properties, we evidence that special care may be required if one strives for highly accurate vertical transition energies. Indeed, comparing all-electron and valence-only calculations, we show that using pseudopotentials with the associated basis sets can induce differences of the order of 0.05 eV on the excitation energies. Fortunately, a reasonable estimate of this shift can be estimated at the sCI level.

physics.chem-ph↗

arXiv2019

Evaluating 0-0 Energies with Theoretical Tools: a Short Review

For a given electronic excited state, the 0-0 energy ($T_0$ or $T_{00}$) is the simplest property allowing straightforward and physically-sound comparisons between theory and (accurate) experiment. However, the computation of 0-0 energies with \emph{ab initio} approaches requires determining both the structure and the vibrational frequencies of the excited state, which limits the quality of the theoretical models that can be considered in practice. This explains why only a rather limited, yet constantly increasing, number of works have been devoted to the determination of this property. In this contribution, we review these efforts with a focus on benchmark studies carried out for both gas phase and solvated compounds. Over the years, not only as the size of the molecules increased, but the refinement of the theoretical tools has followed the same trend. Though the results obtained in these benchmarks significantly depend on both the details of the protocol and the nature of the excited states, one can now roughly estimate, in the case of valence transitions, the overall accuracy of theoretical schemes as follows: $1$ eV for CIS, $0.2$--$0.3$ eV for CIS(D), $0.2$--$0.4$ eV for TD-DFT when one employs hybrid functionals, $0.1$--$0.2$ eV for ADC(2) and CC2, and $0.04$ eV for CC3, the latter approach being the only one delivering chemical accuracy on a near-systematic basis.

physics.chem-ph↗

arXiv2019

General Approach To Compute Phosphorescent OLED Efficiency

Phosphorescent organic light-emitting diodes (PhOLEDs) are widely used in the display industry. In PhOLEDs, cyclometalated Ir(III) complexes are the most widespread triplet emitter dopants to attain red, e.g., Ir(piq)3 (piq = 1-phenylisoquinoline), and green, e.g., Ir(ppy)3 (ppy = 2-phenylpyridine), emissions, whereas obtaining operative deep-blue emitters is still one of the major challenges. When designing new emitters, two main characteristics besides colors should be targeted: high photostability and large photoluminescence efficiencies. To date, these are very often optimized experimentally in a trial-and-error manner. Instead, accurate predictive tools would be highly desirable. In this contribution, we present a general approach for computing the photoluminescence lifetimes and efficiencies of Ir(III) complexes by considering all possible competing excited-state deactivation processes and importantly explicitly including the strongly temperature-dependent ones. This approach is based on the combination of state-of-the-art quantum chemical calculations and excited-state decay rate formalism with kinetic modeling, which is shown to be an efficient and reliable approach for a broad palette of Ir(III) complexes, i.e., from yellow/orange to deep-blue emitters.

physics.chem-ph↗

arXiv2019

Modelling the photochrome-TiO2 interface with Bethe-Salpeter and TD-DFT methods

Hybrid organic/inorganic-semiconductor systems have important applications in both molecular electronics and in photo-responsive materials. The characterization of the interface and of the electronic excited-states of these hybrid systems remains a challenge for state-of-the-art computational methods, as the systems of interest are large. In the present investigation, we present for the first time a many-body Green's function Bethe-Salpeter investigation of a series of photochromic molecules adsorbed onto TiO2 nanoclusters. Based on these studies, the performance of TD-DFT is assessed. Using a state-of-the-art computational protocol, the photochromic properties of different hybrid systems are assessed. This work shows that qualitatively different conclusions can be reached with TD-DFT relying on various exchange-correlation functionals for such organic/inorganic interfaces, and paves the way to more accurate simulation of many materials.

physics.chem-ph↗

arXiv2019

Thermal equilibration between excited states or solvent effects: unveiling the origins of anomalous emissions in heteroleptic Ru(II) complexes

In this manuscript we present a computational study on the photoluminescence properties of several heteroleptic [Ru(H)(CO)(N^N)(tpp)2]+ complexes (tpp = triphenylphosphine). A special focus is set on disentangling the temperature-dependent emissive properties. Experimentally, when cooling a solution of [Ru(H)(CO)(dmphen)(tpp)2]+ (dmphen = 5,6-dimethyl-1,10-phenanthroline) from room to cryogenic temperature, a partial emission switch from metal-to-ligand charge transfer (3MLCT) to ligand-centered (3LC) phosphorescence is observed, resulting in dual photoluminescence. Two different origins of the anomalous emissions are possible, i.e., thermal equilibration between electronically excited states or different excited state solvent relaxation effects. Our calculations are in favor of the thermally equilibrated scenario. This computational investigation highlights the importance of controlling the temperature-dependent emissive behavior for optoelectronic applications.

physics.chem-ph↗

arXiv2018

Reference Energies for Double Excitations

Excited states exhibiting double excitation character are notoriously difficult to model using conventional single-reference methods, such as adiabatic time-dependent density-functional theory (TD-DFT) or equation-of-motion coupled cluster (EOM-CC). In the present work, we provide accurate reference excitation energies for transitions involving a substantial amount of double excitation using a series of increasingly large diffuse-containing atomic basis sets. Our set gathers 20 vertical transitions from 14 small- and medium-size molecule. Depending on the size of the molecule, selected configuration interaction (sCI) and/or multiconfigurational calculations are performed in order to obtain reliable estimates of the vertical transition energies. In addition, coupled cluster approaches including at least contributions from iterative triples are assessed. Our results clearly evidence that the error in CC methods is intimately related to the amount of double excitation character of the transition. For "pure" double excitations (i.e. for transitions which do not mix with single excitations), the error in CC3 can easily reach 1 eV, while it goes down to few tenths of an eV for more common transitions (like in \emph{trans}-butadiene) involving a significant amount of singles. As expected, CC approaches including quadruples yield highly accurate results for any type of transitions. The quality of the excitation energies obtained with multiconfigurational methods is harder to predict. We have found that the overall accuracy of these methods is highly dependent of both the system and the selected active space. The inclusion of the $σ$ and $σ^*$ orbitals in the active space, even for transitions involving mostly $π$ and $π^*$ orbitals, is mandatory in order to reach high accuracy. A theoretical best estimate (TBE) is reported for each transition.

physics.chem-ph↗

arXiv2018

Chemically Accurate 0-0 Energies with not-so-Accurate Excited State Geometries

Using a series of increasingly refined wavefunction methods able to tackle electronic excited states, namely ADC(2), CC2, CCSD, CCSDR(3) and CC3, we investigate the interplay between geometries and 0-0 energies. We show that, due to a strong and nearly systematic error cancelation between the vertical transition and geometrical reorganization energies, CC2 and CCSD structures can be used to obtain chemically-accurate 0-0 energies, though the underlying geometries are rather far from the reference ones and would deliver significant errors for many chemical and physical properties. This indicates that obtaining 0-0 energies matching experiment does not demonstrate the quality of the geometrical parameters. In contrast, accurate computation of vertical excitation energies is mandatory in order to reach chemical accuracy. By determining CC3 total energies on CCSD structures, we model a large set of compounds (including radicals) and electronic transitions (including singlet-triplet excitations) and successfully reach chemical accuracy in a near systematic way. Indeed, for this particular set, our protocol delivers a mean absolute error as small as $0.032$ eV, chemical accuracy (error smaller than $1$ kcal.mol$^{-1}$ or $0.043$ eV) being obtained in 80\%\ of the cases. In only three cases the error exceeds $0.15$ eV which is of the order of the typical error provided by TD-DFT or second-order wavefunction methods for this particular property. The present composite protocol is therefore very effective despite the fact that the geometries may not be considered as very accurate.

physics.chem-ph↗

arXiv2018

A Mountaineering Strategy to Excited States: Highly-Accurate Reference Energies and Benchmarks

Striving to define very accurate vertical transition energies, we perform both high-level coupled cluster (CC) calculations (up to CCSDTQP) and selected configuration interaction (sCI) calculations (up to several millions of determinants) for 18 small compounds. By systematically increasing the order of the CC expansion, the number of determinants in the CI expansion as well as the size of the one-electron basis set, we have been able to reach near full CI (FCI) quality transition energies. These calculations are carried out on CC3/aug-cc-pVTZ geometries, using a series of increasingly large atomic basis sets systematically including diffuse functions. In this way, we define a list of 110 transition energies for states of various characters to be used as references for further calculations. Benchmark transition energies are provided at the aug-pVTZ level as well as with additional basis set corrections, in order to obtain results close to the complete basis set limit. These reference data are used to benchmark a series of twelve excited-state wave function methods accounting for double and triple contributions, namely ADC(2), ADC(3), CIS(D), CIS(D$_\infty$), CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, CC3, CCSDT and CCSDTQ. It turns out that CCSDTQ yields a negligible difference with the extrapolated CI values with a mean absolute error as small as $0.01$ eV, whereas the coupled cluster approaches including iterative triples are also very accurate (mean absolute error of $0.03$ eV). Consequently, CCSDT-3 and CC3 can be used to define reliable benchmarks. This observation does not hold for ADC(3) that delivers quite large errors for this set of small compounds, with a clear tendency to overcorrect its second-order version, ADC(2). Finally, we discuss the possibility to use basis set extrapolation approaches so as to tackle more easily larger compounds.

physics.chem-ph↗