XC Functionals Research Articles

Uncovering the Thermo-Kinetic Origins of Phase Ordering in Mixed-Valence Antimony Tetroxide by First-Principles Modeling.

Phase ordering in the mixed-valence oxide Sb2O4 has been examined by density functional theory (DFT) calculations. We find that the ground-state total energies of the two phases (α and β) are almost degenerate and are highly sensitive to the choice of the approximation to the exchange correlation (xc) functional used in our calculations. Interestingly, with the inclusion of the zero-point energy corrections, the α phase is predicted to be the ground state polymorph for most xc functionals used. We also illustrate the pronounced stereochemical activity of Sb in these polymorphs of Sb2O4, setting an exception to the Keve and Skapski rule. Here, we find that the actual bonding in the α phase is more asymmetric, while the anomalous stability of the β phase could be rationalized from kinetic considerations. We find a non-negligible activation barrier for this α-β phase transition, and the presence of a saddle point (β phase) supports the separation of Sb(III) over a continuous phase transition, as observed in experiments.

Examining the Effect of Exchange-Correlation Approximations in First-Principles Dynamics Simulation of Interfacial Charge Transfer.

We examine the extent to which the exchange-correlation (XC) approximation influences modeling interfacial charge transfer using fewest-switches surface hopping (FSSH) simulations within the single-particle description. A heterogeneous interface between a lithium ion and an extended boron-nitride sheet was considered here, being an extreme case in which wave function localization and energy level alignments are highly sensitive to the XC approximation. The PBE0 hybrid XC approximation yields nonadiabatic couplings (NACs) that are significantly smaller than the values obtained from the PBE-GGA approximation by an order of magnitude for localized electronic states. This difference between the two XC functionals for the calculated NACs was found to derive mainly from the wave function characteristics rather than from the lattice movement although first-principles molecular dynamics trajectories, along which NACs are obtained, differ noticeably between the two XC functionals. Using the NACs and single-particle energy level alignments at different levels of theory, FSSH simulations were performed to model the electron transfer dynamics at the interface. The electron transfer time scale was found to vary as much as, but not more than, 1 order of magnitude. The time scale was found to be quite sensitive to both NACs and energy level alignments. While the order of magnitude consistency for the charge transfer rate is encouraging even for this rather extreme model of heterojunction interface, continued advancement in electronic structure methods is required for quantitatively accurate determination of the transfer rate.

Assessing Density Functional Theory Approaches for Predicting the Structure and Relative Energy of Salicylideneaniline Molecular Switches in the Solid State

The geometrical structures of salicylideneaniline (anil) molecular switches in the solid state have been determined using periodic structure calculations and a variety of density functional theory (DFT) exchange-correlation (XC) functionals, of which several have been tuned for the solid state. The first target was on predicting the unit cell and intramolecular geometrical parameters for three anil derivatives, i.e., the (E)-2-methoxy-6-(pyridine-3-yliminomethyl)phenol (PYV3) and N-(5-chloro-2-hydroxybenzylidene)-aniline (HC) crystals, where the enol (E) form is dominant in the crystalline state at low temperature (∼100 K), and the N-(5-chloro-2-hydroxybenzylidene)-hydroxyaniline (POC) crystal, which is mostly composed of the keto (K) form. The best performance for the unit cell parameters, in comparison with single-crystal X-ray diffraction (XRD) data, is achieved with XC functionals developed for the solid state (PBEsol and PBEsol0) as well as with ωB97X. On the other hand, the differences between the f...

How strongly do hydrogen and water molecules stick to carbon nanomaterials?

The interaction strength of molecular hydrogen and water to carbon nanomaterials is relevant to, among many applications, hydrogen storage, water treatment, and water flow. However, accurate interaction energies for hydrogen and water with carbon nanotubes (CNTs) remain scarce despite the importance of having reliable benchmark data to inform experiments and to validate computational models. Here, benchmark fixed-node diffusion Monte Carlo (DMC) interaction energies are provided for hydrogen and water monomers inside and outside a typical zigzag CNT. The DMC interaction energies provide valuable insight into molecular interactions with CNTs in general and are also expected to be particularly relevant to gas uptake studies on CNTs. In addition, a selection of density functional theory (DFT) exchange-correlation (xc) functionals and force field potentials that ought to be suitable for these systems is compared. An unexpected variation is found in the performance of DFT van der Waals (vdW) models in particular. An analysis of the peculiar discrepancy between different vdW models indicates that medium-range correlation (at circa 3 to 5 Å) plays a key role inside CNTs and is poorly predicted by some vdW models. Using accurate reference information, this work reveals which xc functionals and force fields perform well for molecules interacting with CNTs. The findings will be valuable to future work on these and related systems that involve molecules interacting with low-dimensional systems.

Exact ensemble density functional theory for excited states in a model system: Investigating the weight dependence of the correlation energy

Ensemble density functional theory (eDFT) is an exact time-independent alternative to time-dependent DFT (TD-DFT) for the calculation of excitation energies. Despite its formal simplicity and advantages in contrast to TD-DFT (multiple excitations, for example, can be easily taken into account in an ensemble), eDFT is not standard which is essentially due to the lack of reliable approximate exchange-correlation (xc) functionals for ensembles. Following Smith et al. [Phys. Rev. B 93, 245131 (2016)], we propose in this work to construct an exact eDFT for the nontrivial asymmetric Hubbard dimer, thus providing more insight into the weight dependence of the ensemble xc energy in various correlation regimes. For that purpose, an exact analytical expression for the weight-dependent ensemble exchange energy has been derived. The complementary exact ensemble correlation energy has been computed by means of Legendre--Fenchel transforms. Interesting features like discontinuities in the ensemble xc potential in the strongly correlated limit have been rationalized by means of a generalized adiabatic connection formalism. Finally, functional-driven errors induced by ground-state density-functional approximations have been studied. In the strictly symmetric case or in the weakly correlated regime, combining ensemble exact exchange with ground-state correlation functionals gives relatively accurate ensemble energies. However, when approaching the equiensemble in the strongly correlated regime, this approximation leads to highly curved ensemble energies with negative slope which is unphysical. Using both ground-state exchange and correlation functionals gives much better results in that case. In fact, exact ensemble energies are almost recovered in some density domains. The analysis of density-driven errors is left for future work.

Matildite versus schapbachite: First-principles investigation of the origin of photoactivity inAgBiS2

Recent experiments motivated by solar light harvesting applications have brought a renewed interest in $\mathrm{AgBi}{\mathrm{S}}_{2}$ as an environmentally friendly material with appealing photovoltaic properties. The lack of detailed knowledge on its bulk structural and electronic structure however inhibits further development of this material. Here we have investigated by first-principles quantum mechanical methods models of the two most commonly reported $\mathrm{AgBi}{\mathrm{S}}_{2}$ crystal structures, the room temperature matildite structure, and the metastable schapbachite. Density functional theory (DFT) based calculations using the Perdew-Burke-Ernzerhof exchange-correlation (xc) functional reveal that matildite can be 0.37 eV per $\mathrm{AgBi}{\mathrm{S}}_{2}$ stoichiometry unit more stable than a schapbachite structure in bulk, and that the latter, in its ordered form, may display a metallic electronic structure, precluding its use for solar light harvesting. This points out the fact that $\mathrm{AgBi}{\mathrm{S}}_{2}$ nanocrystals used in solar cells should present a structure based on matildite. Matildite is found to be an indirect gap semiconductor, with an estimated band gap of $\ensuremath{\sim}1.5\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ according to DFT based calculations using the more accurate hybrid xc functionals. These reveal that hole effective mass is twice that of electron effective mass, with concomitant consequences for the generated exciton. Hybrid DFT calculations also show that matildite has a high dielectric constant pertinent to that of an ionic semiconductor and slightly higher than that of PbS, a material that has been extensively used in solar cells in its nanocrystalline form. The calculated Bohr exciton radius of 4.6 nm and the estimated absorption coefficient of ${10}^{5}\phantom{\rule{4pt}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ within the solar light spectrum are well in line with those experimentally reported in the literature.

Global reaction route mapping of water-catalysed gas phase oxidation of glyoxylic acid with hydroxyl radical

In order to assess the potential role of a single water molecule as a catalyst, the gas-phase oxidation reaction of hydroxyl radical with glyoxylic acid has been investigated by the means of quantum mechanical computations using CCSD(T), MP2 and DFT methods. The pre-reaction complexes along the oxidation pathways are systematically explored through a global reaction route mapping method. The computations reveal that a single water molecule stabilizes the pre-reaction complexes as well as respective transition states, resulting in the lowering of the energy barrier, however, the transition state theory computed rate constants for the water-catalysed pathways are found to be an order of magnitude lower than that for the water-free pathways. Notably, the abstraction of formyl hydrogen is observed to be most favourable both in the presence and absence of a single water molecule. Besides these, a couple of triple-proton exchange pathways involving simultaneous proton transfer between the glyoxylic acid, OH radical and a single water molecule are also explored. All the pathways are observed to proceed through conventional free radical mechanism when analysed using BHandHLYP exchange–correlation (XC) functional of DFT. However, DFT method using other XC functionals revealed that one of the relevant acidic H-abstraction pathways proceeds through a proton-coupled electron-transfer mechanism and also results in the dissociation of glyoxylic acid. The pathways for trans form of glyoxylic acid has also been compared with those explored for the cis form. The standard Gibbs free-energy profiles for the reactions studied indicate that the hydrogen abstraction, particularly in trans-glyoxylic acid, may be more feasible than the dissociation, particularly at lower temperatures. This study may assist future investigation of similar atmospheric reactions.

Electronic excitation and injection of Ru-N3 dye anchored to TiO2 surface

A step-by-step theoretical protocol based on the density functional theory (DFT) and time-dependent DFT (TD-DFT) has been performed to study a Ruthenium polypyridyl complex named cis-dithiocyanatobis-(4,4′-dicarboxy-2,2′-bipyridine) ruthenium(II) (N3) sensitized TiO2 solar cell including dye excitations and electronic injection. Three binding structures of N3 anchored to a TiO2 nanoparticle (TiO2)38 have been adopted. The electronic structures and optical properties of N3 dye in gas phase, in solutions (with the explicit and implicit solvent models), and interfaced with TiO2 have been calculated. The hybrid DFT exchange-correlation (XC) functional B3LYP and PBE0, the newly-modified PBE0 functional PBE0-1/3, and the long-range corrected DFT (LRC-DFT) XC functional Cam-B3LYP have been applied. It is found that both the DFT XC functionals and molecular environments play a crucial role on molecular properties, which affect both the spectral lineshapes and peak positions. Coupled with PCM model, TD-PBE0-1/3 produces the best result compared with the experimental spectrum of N3 in CH2Cl2, TD-B3LYP slightly underestimates the excitation energies, and TD-Cam-B3LYP overestimates the excitation energies of 0.4–0.5eV. As the solvent polarity increases, the electronic absorption spectra of N3 dye blue shift. The absorption manners of N3 anchored to (TiO2)38 affect the electronic excitations, leading to different electronic injection pathways. Two of three anchoring manners favor the interfacial electronic transfer. In the end, three possible electronic injection pathways from the different parts of the excited dye to TiO2 nanoparticle have been suggested, indicating the different timescales of electron injections.

Implementation Strategies for Orbital-dependent Density Functionals

The development of density functional theory (DFT) has been focused primarily on two main pillars: (1) the pursuit of more accurate exchange-correlation (XC) density functionals; (2) the feasibility of computational implementation when dealing with many-body systems. In this context, this work is aimed on using one-dimensional quantum systems as theoretical laboratories to investigate the implementation of orbital functionals (OFs) of density. By definition, OFs are those which depend only implicitly on the density, via an explicit formulation in terms of Kohn-Sham orbitals. Typical examples are the XC functionals arising from the Perdew-Zunger self-interaction correction (PZSIC). Formally, via Kohn-Sham equations, the implementation of OFs must be performed by means of the optimized effective potential method (OEP), which is known by requiring an excessive computational effort even when dealing with few electrons systems. Here, we proceed a systematical investigation aiming to simplify or avoid the OEP procedure, taking as reference the implementation of the PZSIC correction applied to one-dimensional Hubbard chains.

Kinetic‐energy‐density dependent semilocal exchange‐correlation functionals

AbstractWe present the theory of semilocal exchange‐correlation (XC) energy functionals which depend on the Kohn–Sham kinetic energy density (KED), including the relevant class of meta‐generalized gradient approximation (meta‐GGA) functionals. Thanks to the KED ingredient, meta‐GGA functionals can satisfy different exact constraints for XC energy and can be made one‐electron self‐correlation free. This leads to a better accuracy over a wider range of properties with respect to GGAs, often reaching the accuracy of hybrid functionals, but at much reduced computational cost. An extensive survey of the relevant literature on existing KED dependent XC functionals is provided, considering nonempirical, semi‐empirical, and fully empirical ones. A deeper analysis and a wide benchmark are presented for functionals derived considering only exact constraints and parameters obtained from model and/or atomic systems.

Electronic properties of the FeSe/STO interface from first-principle calculations

We perform first-principle calculations of the FeSe monolayer on STO with the focus on three central aspects. First, compared to experiment, the bulk lattice constant of FeSe is too small in LDA, PBEsol and Perdew–Burgke–Ernzerhof (PBE) type exchange-correlation (xc) functionals while in bulk SrTiO3 (STO) LDA over-binds, PBE under-binds and PBEsol agrees best with experiment. Thus, the strain in the FeSe monolayer on STO depends on the xc functional and, especially in the non-magnetic state, is strongly overestimated and best described in PBEsol. In agreement with earlier work, we find that the band structure of the checkerboard antiferromagnetic configuration agrees best with experiment where, in addition, the relative strain on FeSe is best described. Second, our focus is on the crystal structure of the interface itself. The FeSe/STO distance depends weakly on the presence of magnetism and PBE results agree best with recent experimental data. We find that a double -layer below the FeSe relaxes to a structure in disagreement with experimental data. On the other hand, considering the effect of oxygen-vacancies in the single terminated slab within the virtual crystal approximation, in agreement with recent experiment, the FeSe monolayer Ti layer distance increases for a small vacancy concentration (<20%). Third, we investigate the charge-transfer to FeSe due to oxygen-vacancies in STO. Interestingly, we find negligible charge transfer for small concentrations—only above 20% a significant charge transfer is observed.

Assessing the influence of van der Waals corrected exchange-correlation functionals on the anisotropic mechanical properties of coinage metals

Current materials-related calculations employ density-functional theory (DFT), commonly using the (semi-)local-density approximations for the exchange-correlation (xc) functional. The difficulties in arriving at a reasonable description of van der Waals (vdW) interactions by DFT-based models is to date a big challenge. In this work, we use various flavors of vdW-corrected DFT xc functionals---ranging from the quasiempirical force-field add-on vdW corrections to self-consistent nonlocal correlation functionals---to study the bulk lattice and mechanical properties (including the elastic constants and anisotropic indices) of the coinage metals (copper, silver, and gold). We critically assess the reliability of the different vdW-corrected DFT methods in describing their anisotropic mechanical properties which have been less reported in the literature. In the context of this work, we regard that our results reiterate the fact that advocating a so-called perfect vdW-inclusive xc functional for describing the general physics and chemistry of these coinage metals could be a little premature. These challenges to modern-day functionals for anisotropically strained coinage metals (e.g., at the faceted surfaces of nanostructures) may well be relevant to other strained material systems.

Synthesis, Crystal Structure and Comparative DFT Studies of a 1D Ni(II) Polymeric Complex of 2-Hydroxypyridine-N-oxide

A novel Nickel (II) complex of 2-hydroxypyridine-N-oxide has been prepared and characterized by X-ray crystal structure analysis, FT-IR, UV spectra and thermogravimetry. The X-ray diffraction study reveals that the nickel complex is a 1D linear polymer in space group Pī with a = 6.250(1), b = 8.746(2), c = 9.462(2) A, α = 81.76(3)o, β = 79.55(3)o and γ = 81.17(3)o. Two nickel ions are present in the unit cell related by the crystallographic centre of symmetry at ½ ½ ½. There are two different short non-bonded Ni to Ni separations in the polymeric structure: 3.454 and 3.467 A respectively. Both room temperature magnetic moment measurements, and theoretical calculations are in favor of a simple paramagnetic system. As a complementary study, plane wave pseudopotential DFT calculations were performed, utilizing eight different XC functionals. The PBE and PBE0 functionals reproduce well the X-ray crystal structure of the complex, while the HSE functional gives a band gap which corresponds reasonably to the experimentally estimated value. The results of antimicrobial properties and thermal analysis of the complex are also reported. The preparation, crystallization and X-ray analysis of a novel 1D polymeric Nickel (II) complex of 2-hydroxypyridine-N-oxide and its characterization by FT-IR, UV spectra, thermogravimetry and possible therapeutics via antimicrobial studies are described.

Importance of finite-temperature exchange correlation for warm dense matter calculations.

The effects of an explicit temperature dependence in the exchange correlation (XC) free-energy functional upon calculated properties of matter in the warm dense regime are investigated. The comparison is between the Karasiev-Sjostrom-Dufty-Trickey (KSDT) finite-temperature local-density approximation (TLDA) XC functional [Karasiev etal., Phys. Rev. Lett. 112, 076403 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.076403] parametrized from restricted path-integral Monte Carlo data on the homogeneous electron gas (HEG) and the conventional Monte Carlo parametrization ground-state LDA XC [Perdew-Zunger (PZ)] functional evaluated with T-dependent densities. Both Kohn-Sham (KS) and orbital-free density-functional theories are used, depending upon computational resource demands. Compared to the PZ functional, the KSDT functional generally lowers the dc electrical conductivity of low-density Al, yielding improved agreement with experiment. The greatest lowering is about 15% for T=15 kK. Correspondingly, the KS band structure of low-density fcc Al from the KSDT functional exhibits a clear increase in interband separation above the Fermi level compared to the PZ bands. In some density-temperature regimes, the deuterium equations of state obtained from the two XC functionals exhibit pressure differences as large as 4% and a 6% range of differences. However, the hydrogen principal Hugoniot is insensitive to the explicit XC T dependence because of cancellation between the energy and pressure-volume work difference terms in the Rankine-Hugoniot equation. Finally, the temperature at which the HEG becomes unstable is T≥7200 K for the T-dependent XC, a result that the ground-state XC underestimates by about 1000 K.

Critical Assessment of Time-Dependent Density Functional Theory for Excited States of Open-Shell Systems: II. Doublet-Quartet Transitions

Compared with closed-shell systems, open-shell systems place three additional challenges to time-dependent density functional theory (TD-DFT) for electronically excited states: (a) the spin-contamination problem is a serious issue; (b) the exchange-correlation (XC) kernel may be numerically instable; and (c) the single-determinant description of open-shell ground states readily becomes energetically instable. Confined to flip-up single excitations, the spin-contamination problem can largely be avoided by using the spin-flip TD-DFT (SF-TD-DFT) formalism, provided that a noncollinear XC kernel is employed. As for the numerical instabilities associated with such a kernel, only an ad hoc scheme has been proposed so far, viz., the ALDA0 kernel, which amounts to setting the divergent components (arising from density gradients and kinetic energy density) simply to zero. The ground-state instability problem can effectively be avoided by introducing the Tamm-Dancoff approximation (TDA) to TD-DFT. Therefore, on a general basis, the SF-TDA/ALDA0 Ansatz is so far the only promising means within the TD-DFT framework for flip-up single excitations of open-shell systems. To assess systematically the performance of SF-TDA/ALDA0, in total 61 low-lying quartet excited states of the benchmark set of 11 small radicals [J. Chem. Theory Comput. 2016, 12, 238] are investigated with various XC functionals. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as benchmark, it is found that the mean absolute errors of SF-TDA/ALDA0 with the SAOP (statistical averaging of model orbital potentials), global hybrid, and range-separated hybrid functionals are in the range of 0.2-0.4 eV. This is in line not only with the typical accuracy of TD-DFT for singlet and triplet excited states of closed-shell systems but also with the gross accuracy of spin-adapted TD-DFT for spin-conserving excited states of open-shell systems.

Comparative assessment of density functional methods for evaluating essential parameters to simulate SERS spectra within the excited state energy gradient approximation

The prospect of challenges in reproducing and interpretation of resonance Raman properties of molecules interacting with metal clusters has prompted the present research initiative. Resonance Raman spectra based on the time-dependent gradient approximation are examined in the framework of density functional theory using different methods for representing the exchange-correlation functional. In this work the performance of different XC functionals in the prediction of ground state properties, excitation state energies, and gradients are compared and discussed. Resonance Raman properties based on time-dependent gradient approximation for the strongly low-lying charge transfer states are calculated and compared for different methods. We draw the following conclusions: (1) for calculating the binding energy and ground state geometry, dispersion-corrected functionals give the best performance in comparison to ab initio calculations, (2) GGA and meta GGA functionals give good accuracy in calculating vibrational frequencies, (3) excited state energies determined by hybrid and range-separated hybrid functionals are in good agreement with EOM-CCSD calculations, and (4) in calculating resonance Raman properties GGA functionals give good and reasonable performance in comparison to the experiment; however, calculating the excited state gradient by using the hybrid functional on the hessian of GGA improves the results of the hybrid functional significantly. Finally, we conclude that the agreement of charge-transfer surface enhanced resonance Raman spectra with experiment is improved significantly by using the excited state gradient approximation.

Perspective: How good is DFT for water?

Kohn-Sham density functional theory (DFT) has become established as an indispensable tool for investigating aqueous systems of all kinds, including those important in chemistry, surface science, biology, and the earth sciences. Nevertheless, many widely used approximations for the exchange-correlation (XC) functional describe the properties of pure water systems with an accuracy that is not fully satisfactory. The explicit inclusion of dispersion interactions generally improves the description, but there remain large disagreements between the predictions of different dispersion-inclusive methods. We present here a review of DFT work on water clusters, ice structures, and liquid water, with the aim of elucidating how the strengths and weaknesses of different XC approximations manifest themselves across this variety of water systems. Our review highlights the crucial role of dispersion in describing the delicate balance between compact and extended structures of many different water systems, including the liquid. By referring to a wide range of published work, we argue that the correct description of exchange-overlap interactions is also extremely important, so that the choice of semi-local or hybrid functional employed in dispersion-inclusive methods is crucial. The origins and consequences of beyond-2-body errors of approximate XC functionals are noted, and we also discuss the substantial differences between different representations of dispersion. We propose a simple numerical scoring system that rates the performance of different XC functionals in describing water systems, and we suggest possible future developments.

Structural and response properties of all BaTiO3 phases from density functional theory using the projector-augmented-wave methods

A study of ground state properties of bulk BaTiO3 perovskite crystal was conducted using first-principles density functional theory with local-density approximation (LDA) and generalized-gradient approximation (GGA), using the projector-augmented wave methods. Two different PAW potentials developed by Jollet–Torrent–Holzwarth (JTH) and Garrity–Bennett–Rabe–Vanderbilt (GBRV) are employed in the calculations. This study emphasize on electronic, structural and response properties of all BaTiO3 phases using different exchange correlation (XC) functionals and PAW potentials. Lattice parameters, cohesion energy, bulk modulus, Born effective charge, spontaneous polarization and charge densities of all BaTiO3 phases are calculated. In addition, gamma point phonon frequencies are computed with LDA. Structural and vibrational properties predicted using the two PAW potentials are consistent with experimental and previous theoretical studies for all BaTiO3 phases. It is observed that calculations with GGA yields structural properties much closer to reported experimental values than LDA. Spontaneous polarization computed using Berry phase approach for the three structures in ferroelectric phase are consistent with other theoretical results, but differ considerably from experimental values. The deviation of lattice parameters computed using different XC functionals directly affects the computed spontaneous polarization. An analysis of phonon mode symmetries and frequencies conformed to experimental findings in the literature.

Density functional theory study on the magnetic properties of Co3O4 with normal spinel structure

The magnetic properties of Co3O4 with a normal spinel structure were investigated via the full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). The exchange and correlation effects between electrons were treated with a standard generalized gradient approximation (GGA) from Perdew–Burke–Ernzerhof (PBE), as a function of the on-site Coulomb U term, the GGA−PBE+U method, and a B3PW91 hybrid functional with different Hartree–Fock exchange admixtures. Were calculated all of these exchange–correlation (XC) functionals both with and without spin–orbit coupling (SOC). The objective for these calculations was to predict the ground-state magnetic structure of Co3O4 crystal using different XC functionals and to investigate the influence that SOC had on these results. All of our calculations confirmed that the collinear antiferromagnetic (AFM) order was energetically more favorable than the ferromagnetic (FM) one, which agrees with experimental findings. This conclusion was not influenced by the XC functional type employed or whether the spin–orbit effect was used. Thus, the present work does not confirm the recent DFT plane wave pseudopotential results that when including spin–orbit effects, the calculations determined that the collinear FM state had lower energy than the AFM one.

Benchmarking TD-DFT against Vibrationally Resolved Absorption Spectra at Room Temperature: 7-Aminocoumarins as Test Cases.

Time-dependent density functional theory (TD-DFT) is usually benchmarked by evaluating how the vertical excitation energies computed by using different exchange-correlation (XC) functionals compare with the maximum of the absorption spectra. However, the latter does not necessarily coincide with the vertical energies because it is affected by the vibronic band structure that has to be properly taken into account. In this work, we have evaluated the performance of several functionals belonging to different families in reproducing the vibronic structure (band shape) of four 7-aminocoumarin molecules of technological interest, whose spectra have been recorded in methylcyclohexane and acetonitrile solvents. In order to compare the computed vibronic spectra with the experimental ones in the most consistent way, the effect of temperature, often neglected, was also taken into account. We have found that no single functional provides simultaneously accurate band positions and shapes, but the combination of ωB97X vibronic couplings with PBE0 vertical energies can lead to very satisfactory results. In addition to the assessment of XC functionals, several adiabatic and vertical models proposed in the literature to compute vibrationally resolved electronic spectra have been tested and validated with respect to experiments. On these grounds, the adiabatic Hessian model has been used to perform a complete analysis of the ωB97X/PBE0 vibronic transitions contributing to the final band shapes of the investigated aminocoumarin molecules.