Zirconia is a technologically relevant material widely employed in catalysis owing to its thermal stability, acid–base surface properties, and optical response, enabling applications both as a solid acid catalyst and as a photocatalytic material. Even so, the relatively low specific surface area of bulk zirconia may limit its catalytic performance, making supported systems and mixed oxides attractive alternatives for enhancing dispersion and surface accessibility. Among these, zirconia–alumina mixed oxides have attracted significant attention because of the strong interfacial interactions established between both phases, which may involve a migration of Zr4⁺ species into the subsurface region of alumina, leading to the formation of structurally stable mixed oxide domains. This behavior has been associated with modifications in the electronic structure and surface reactivity of the material. In the present work, the UV absorption spectrum of the mixed oxide was calculated, and reasonable agreement was achieved with the measured gap and spectrum, reinforcing the existence of the mixed oxide. The bandgap was determined as 6.47 eV, close to the experimental values, and the simulated spectrum shows good agreement with the experimental profile. The geometry of the mixed oxide was optimized with and without constraint at the DFT/PBE level with periodic boundary conditions, a plane-wave basis set for valence electrons, and projected augmented waves (PAW) to treat core electrons. Excited-state optical properties were evaluated by solving the Bethe–Salpeter equation (BSE) on top of GW quasiparticle energies, allowing an accurate description of electron–hole interactions and optical transitions. All calculations were done in VASP software.

We have investigated the electronic structure and morphology of thin films of the electron-donor poly[(2,6-(4,8-bis(5-(2-ethylhexylthio)-4-fluorothiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5(1 ',3 '-di-2-thienyl-5 ',7 '-bis(2-ethylhexyl)benzo[1 ',2 '-c:4 ',5 '-c ']dithiophene-4,8-dione)] (PBDB-T-SF), the non-fullerene acceptor (NFA) poly[[1,2,3,6,7,8-hexahydro-2,7-bis(2-octyldodecyl)-1,3,6,8-dioxobenzo[lmn][3,8]phenanthroline-4,9-diyl][2,2 '-bithiophene]-5,5 '-diyl] (P(NDI2OD-T2)) and their blend. Angle-resolved near-edge X-ray absorption fine structure (NEXAFS) in total electron yield detection mode was employed to probe the C 1s, N 1s and S 2p absorption edges. The results indicate a preferential face-on orientation of the naphthalene diimide unit in the acceptor, and an edge-on orientation for the thiophene rings. A preferential edge-on orientation was also observed for the electron-donor polymer. Analysis of the blend's NEXAFS spectra suggests an accumulation of the NFA component on the surface of the film. The investigated films were also characterized by X-ray photoelectron spectroscopy (XPS), attesting the presence of thiophene in all the samples and imide in the films containing the NFA polymer. The XPS results further indicate that the acceptor material is accumulated in the surface of the blend film. Finally, the analysis was complemented by ab initio calculations at the multi-configurational level for transitions at C 1s, N 1s and S 2p absorption edges, with spin-orbit effects included for the latter. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

An important class of ligands studied recently is N-heterocyclic carbenes (NHCs) with potential application as a photosensor for solar cells. In this work we investigate organometallic complexes based on [Fe(CNC)2]2+ (CNC = 2,6-bis[3-isopropylimidazol-2-ylidene]pyridine). We selected d6 metals, namely Co(III), Mn(I) and Cr(0), with the same ligands and applied CASSCF/NEVPT2 and TDDFT methods. It is shown that TDDFT is a suitable method, agreeing well with CASSCF/NEVPT2. The potential for use as a photosensor follows the order: Mn(I), Cr(0), Fe(II), and Co(III). The [Mn(CNC)2]+ is shown to the best candidates for photosensitizer due to the higher absorption band in the region of maximum solar radiation and most effective intersystem crossing (ISC) to the triplet state, followed very closely by [Cr(CNC)2].

(1) Background: Ionizing radiation in the Earth’s atmosphere drives key chemical transformations affecting atmospheric composition. Despite their environmental relevance, experimental data on proton collisions with hydrofluorocarbons remain limited, and theoretical models for total cross-sections and stopping power are still underdeveloped. (2) Methods: This study applies Rudd’s semiempirical model to calculate proton impact ionization cross-sections for the CF3CH2F molecule, considering contributions from both outer and inner electron shells. The model enables the estimation of differential cross-sections and the average energy of secondary electrons. In addition, we calculate the photoionization cross-sections using a discretized representation of the continuum—the so-called pseudo-spectrum—obtained through TDDFT with PBE0 as an exchange–correlation functional and compare it with the cross-section obtained for proton impact in the high-energy limit. (3) Results: The Rudd model proves highly adaptable and suitable for numerical applications. However, its validation is hindered by the scarcity of experimental data. Existing models, such as SRIM and Bethe–Bloch, show significant discrepancies due to their limited applicability at intermediate energies and lack of molecular structure consideration. (4) Conclusions: A comparison between the Rudd and BEB models reveals strong agreement in the analyzed energy range. This consistency stems from both models accounting for the molecular structure of the target, as well as from the fact that protons and electrons possess charges of the same magnitude, supporting a coherent description of ionization processes at these energies.

The photoabsorption and infrared spectra (IR) of molecular systems are heavily influenced by aggregation. In the electronic spectra, the vibronic coupling effect is of utmost importance. Although treating both effects simultaneously can be challenging, it is often the only way to explain the experimental spectrum of molecular clusters. In this work, we study IR spectra and the vibronic coupling effect in the electronic photoabsorption spectra in molecular systems composed of benzene (monomer, dimers, and crystal). Photoabsorption spectra were generated using the direct vibronic coupling method at the density functional theory (DFT) level. We also simulated the spectra with the Liouville-Lanczos approach by calculating the electronic transitions along the main inducing modes for two forbidden transitions (1A1g → 1B2u and 1A1g → 1B1u). DFT was also applied to simulate IR spectra. For the monomer, vibronic coupling was crucial to induce the first and second forbidden transitions. On the other hand, molecular aggregation was sufficient to induce the first and second forbidden transitions in almost all dimers. However, when the vibronic coupling is evaluated for the clusters, the band in the energy range of the 1A1g → 1B1u transition is affected both by the aggregation itself and the inducing modes. Moreover, some inducing modes drastically change the allowed 1A1g → 1E1u transition, depending on the dimer under study due to symmetry breaking. In terms of IR spectra, clear signatures are present. For instance, the intensities of the C-H stretching modes decrease as aggregation increases. This work shows that aggregation impacts the band shapes differently in relation to the benzene aggregate structure and the excitation under analysis.

The study of molecular aggregation effects on the electronic spectrum is essential for the development of optoelectronic devices. However, investigating the entire valence absorption spectrum of aggregates using quantum mechanical methods is a challenging task. In this work, we perform systematic simulations of the absorption spectrum of benzene molecular clusters up to 35 eV applying two approaches based on time-dependent density functional theory. The results show that depending on the dimer packing, different energy shifts occur for the symmetry allowed π→π^* transition, in comparison to the monomer. The transition intensity increases for the band around 6 eV for larger aggregates from the monomer to dimers and tetramer, indicating the occurrence of the symmetry forbidden (in D_6h point group) ^1A_1g→ ^1B_1u transition. The benzene crystal exhibits a large redshift following the experimental spectrum. Also, the continuum regions of all spectra show a good agreement with the experiments both in gas and solid phases. Geometry optimization of the monomer was carried out with Gaussian 09 software using the PBE0/def2-TZVP level of theory. We used dimers and tetramer molecular geometries extracted from the experimental crystal structure. The absorption spectra were directly obtained by the Liouville-Lanczos TDDFT approach with plane waves basis set or indirectly by TDDFT pseudo-spectra calculated in a L^2 basis followed by analytic continuation procedure to obtain complex polarizability. The former is available at Quantum ESPRESSO, and the latter was calculated using Gaussian 09 with the post-processing performed with a code previously developed in our group.

Five-membered heterocyclic compounds containing nitrogen atoms are important biomolecule building blocks. In addition to their fundamental biological importance, these molecular structures are used in several technological applications. Consequently, it is essential to develop techniques that allow the characterization of these fundamental systems. We address this issue by performing simulations of K-edge NEXAFS spectra by applying a time-dependent density functional theory (TDDFT) and an inner-shell multiconfigurational self-consistent field (IS-MCSCF) of selected molecules. Also, vibronic coupling simulations were considered for the TDDFT computations. Surprisingly, molecular orbital binding energies do not reproduce the order of the transition energies obtained by IS-MCSCF, indicating a possible breakdown of the orbital picture concerning the NEXAFS spectrum. In general, the TDDFT and IS-MCSCF results are compatible and are in close agreement with experimental data. Moreover, vibronic coupling and vertical transition results were very similar. Finally, it is important to mention that, to the best of our knowledge, this is the first time that the IS-MCSCF method has been applied to molecular systems of this size.

The vicinal effect on chlorination reactions of diols was investigated by computational methods. Applying density functional theory (DFT) combined with polarizable continuum model (PCM) and explicit solvent molecules, we demonstrated the effect of hydration on the leaving and vicinal hydroxyl group in SN2 reactions of selected alcohols. Our results point out to the importance of intermolecular hydrogen bonds as a stabilizing factor in reaction pre-complexes and alcohols with vicinal hydroxyl groups, highlighting the importance of solute-solvent network formation. This indicates the significance of adequately describing the solvent in the study of reaction mechanisms, in special when the interaction with solute molecules and ions are strong. Also, we found a “vinical effect” on the reactivity, in other words, alcohols with vicinal hydroxyl groups exhibit higher activation energies when compared to related monoalcohols. Moreover, 1,3-propanediol and 1,3-butanediol present the highest activation energies.

(1) Background: Fragmentation after double and triple photoionization of the CCl4 molecule in the valence, Cl 2p, and C 1s regions have been reported; (2) Methods: We have used photoion-photoion (PIPICO) coincidence technique combined with synchrotron radiation. In addition, ab initio quantum mechanical calculations were done at multiconfigurational self-consistent and multireference configuration interaction to describe ground and inner-shell states; (3) Results: We have observed coincidences involving singly and doubly charged fragments coming from the doubly and triply ionized molecule. We have also found a well agreement between the quantum mechanical calculations and the total ion yield spectrum. It is shown that the Cl+ ion is the predominant product resulting from the fragmentation of the doubly and triply charged CCl4 molecule. The CCl+ + Cl+ pair is the dominant coincidence in the spectra from valence up to the C 1s edge; (4) Conclusions: The kinetic energy of the fragments is compatible with the Coulomb explosion model.

We present a theoretical study of the coincidence detection process of molecular fragments arising from the dissociation of an excited molecule. We follow an approach proposed in a previous work in which we computed the probability of coincidence detection by applying two detection operators to the molecular wave function in the asymptotic regime, where the atoms are infinitely separated. That approach led us to predict the existence of interference in the probability distribution for the temporal coincidence spectrum due to the different possible rotational levels during the molecular dissociation. In this work, we investigate the detection of H(2s) atoms arising from the dissociation of the hydrogen molecule in the doubly excited state 1Q2 1Eg+ considering a thermal molecular sample excited to the state of interest by electron impact. We refine the previous results, bringing them closer to what is expected experimentally, by computing the occupations of each relevant rotational level from the determination of the generalized oscillator strength with rovibrational resolution.

In the present work, we revisit the spectrum of the hexacyanocobaltate(III) ion, [Co(CN)6]3-, which has been considered a prototype complex in the coordination chemistry, with modern quantum chemistry methods. The main features have been describing by revealing the role of different effects, such as vibronic coupling, solvation and spin-orbit coupling. The UV-vis spectrum is composed by two bands (1A1g → 1T1g and 1A1g → 1T2g), characterized by singlet-singlet metal-centered transitions, and a more intense third one, characterized by charge transfer transition. There is also a small band shoulder. The first two are symmetry-forbidden transitions in the Oh group. Their intensity can only be explained by a vibronic coupling mechanism. For the band shoulder, additional to vibronic coupling, spin-orbit coupling is also necessary, since the transition is characterized as singlet to triplet, 1A1g → 3T1g.

The discovery of C60, C60+, and C70 in the interstellar medium has ignited a profound interest in the astrochemistry of fullerene and related systems. In particular, the presence of diffuse interstellar bands and their association with C60+ has led to the hypothesis that hydrogenated derivatives, known as fulleranes, may also exist in the interstellar medium and contribute to these bands. In this study, we systematically investigated the structural and spectroscopic properties of C60Hn+q (n = 0-4, q = 0,1) using an automated global minimum search and density functional theory calculations. Our results revealed novel global minimum structures for C60H2 and C60H4, distinct from previous reports. Notably, all hydrogenated fullerenes exhibited lower ionization potentials and higher proton affinities compared to C60. From an astrochemical perspective, our results exposed the challenges in establishing definitive spectroscopic criteria for detecting fulleranes using mid-infrared and UV-Vis spectroscopies. However, we successfully identified distinct electronic transitions in the near-infrared range that serve as distinctive signatures of cationic fulleranes. We strongly advocate for further high-resolution experimental studies to fully explore the potential of these transitions for the interstellar detection of fulleranes.

Molybdenum carbide (Mo2C) can be employed as catalyst and the nature of the active sites and reactants are often investigated by adsorption of probe molecules, applying infrared spectroscopy (IR). However, IR analysis is a complex task and theoretical simulations can help. In order to study the adsorption and IR analysis of acrylic acid over Mo2C, we have performed DFT calculations and compared to the experimental results. Radical and dimer formation on the carbide surface were also considered. It was shown that the energetic selection is not enough to rationalize the experimental IR spectrum. The most favorable specie is the adsorbed acrylic acid in the parallel mode. In the limit of dimer formation, the hydrogen bonds great stabilize the parallel adsorption. On the other hand, simulated IR spectra are compatible to parallel dimer as well as parallel and orthogonal monomers. Finally, we identified three possible desorption pathways indicating different desorption temperatures.

The microsolvation effect was investigated on bimolecular nucleophilic substitution (SN2$S_N2$) mechanism for chlorination of methanol, ethanol, and propanol using water as explicit solvent. Based on theoretical calculations, within Density Functional Theory (DFT) combined with polarizable continuum model (PCM) and explicit solvent molecules, it was possible to compare the effect of hydration on the nucleophile and on the leaving group, for the main extremal points of potential surfaces, that is, pre-complex, transition state (TS), and post-complex. The possible disposition of water molecules was also investigated raging from one to four explicit molecules. This study was carefully and systematically done for methanol and the main conclusions were used to guide the corresponding study for ethanol and propanol. The results point out to an increase of activation energy with the number of explicit water molecules, showing the importance of hydrogen bond on the stabilization of structures, effect not captured by PCM alone.

A comparison of four approaches to account the vibronic coupling in photoabsorption is performed. The methods considered are nuclear ensemble (NE), direct vibronic coupling (DVC), adiabatic Hessian (AH), and vertical gradient (VG). The case study is the symmetry-forbidden $$\tilde{X}$$ $$^{1}$$ A $$_1$$ $$\rightarrow$$ $$\tilde{A}$$ $$^{1}$$ A $$_2$$ (n $$\rightarrow$$ $$\pi ^*$$ ) transition in formaldehyde. Being forbidden in the equilibrium geometry, this transition is entirely induced by vibronic coupling and constitutes an appropriate case to study the performance of different methods. From DVC, it is found that mode 1 (C=O out-of-plane bending) is the most inducing, followed by mode 6 (in-plane C-H asymmetric stretching) and finally by mode 2 (in-plane C-H asymmetric bending). We were able to correlate 17 out of 20 structures obtained from NE with these modes, showing that these two methods, although different in principle, give comparable results. The simulated spectra were obtained for all methods and compared, and each one has its own advantage. In what concerns the transition studied, NE gives the best description of the spectrum, DVC is the only one that easily gives an absolute value for OOS, and AH and VG are the computationally less expensive methods. From the latter two, VG is the less demanding on computational grounds, since it does not require the excited state Hessian.

A detailed description of a method proposed to compute total photoionization and photodetachment cross sections of atoms and molecules relying just on L\(^2\) basis sets is presented. The method consists of an analytical continuation procedure based on Padé approximants. It has the advantage of treating the discrete and continuum part of the spectra at the same level with a flexible choice of the correlated electronic structure approximations. Herein, we present results obtained at the coupled cluster singles and doubles (CCSD) and time-dependent density functional theory (TDDFT) level. Examples of L\(^2\) basis sets adequate and inadequate to reproduce the continuum region of the spectrum are given for the CCSD photoionization cross section of He. Also, a brief review of recent applications of the method is presented, together with original TDDFT results for the total photoionization cross section of formic acid, HCOOH, and the photodetachment cross section of the formate anion, HCOO\(^-\).

A new reaction mechanism for the glycerol chlorination is proposed. This mechanism is based on theoretical calculations within density functional theory combined with polarizable continuum model . Two possibilities were investigated, the first is the S(N)2 chlorination forming mono- and dichlorinated products and the second one is through an ester intermediate formed by glycerol esterification in the presence of acetic acid as catalyst. Our results indicate that the first chlorination reaction can occur in the absence of the catalyst and the main product is 3-monochloropropane-1,2-diol (1-MCP). The inhibitory role of water in the second chlorination is also revealed, that is, water formation suppresses the second chlorination when reaction is conducted in the absence of a carboxylic acid. In the presence of the catalyst, oxonium species are formed as reaction intermediates and the main products are 1-MCP and 1,3-dichloropropan-2-ol (1,3-DCP). Our results are in agreement with the experimental data, which indicate that the 1,3-DCP is the main product when an acid catalyst is employed and, also, there is no significant formation of 2-monochloropropane-1,2-diol and 1,2-dichloropropan-3-ol .

Rotational spectroscopy plays a major role in the field of observational astrochemistry, enabling the detection of more than 200 species including a plethora of complex organic molecules in different space environments. Those line detections allow correctly determining the sources and physical properties, as well as exploring their morphology, evolutionary stage, and chemical evolution pathways. In this context, quantum chemistry is a powerful tool to the investigation of the molecular inventory of astrophysical environments, guiding laboratory experiments and assisting in both line assignments and extrapolation of the experimental data to unexplored frequency ranges. In the present work, we start by briefly reviewing the rotational model Hamiltonian for asymmetric tops beyond the rigid-rotor approximation, including rotational-vibrational, centrifugal, and anharmonic effects. Then, aiming at further contributing to the recording and analysis of laboratory microwave spectroscopy by means of accessible, less demanding quantum chemical methods, we performed density functional theory (DFT) calculations of the spectroscopic parameters of astrochemically relevant species, followed by their rotational spectrum simulations. Furthermore, dispersion-correction effects combined with different functionals were also investigated. Case studies are the asymmetric tops H2CO, H2CS, c-HCOOH, t-HCOOH, and HNCO. Spectroscopic parameter predictions were overall very close to experiment, with mean percentage errors smaller than 1% for zeroth order and $\sim 5\%$ for first-order constants. We discuss the implications and impacts of those constants on spectrum simulations, and compare line-frequency predictions at millimeter wavelengths. Moreover, theoretical spectroscopic parameters of c-HCOOH and HNCO are introduced for the first time in this work.

A theoretical study of the K-shell total photoabsorption and photoionization cross section spectra of water and ammonia bonded to benzene (C6H6) and the polycyclic aromatic hydrocarbons (PAHs) naphthalene (C10H8), coronene (C24H12) and circumcoronene (C54H18) by van der Waals (vdW) forces is presented. The discretized electronic pseudospectra at the oxygen and nitrogen K-edges, covering the discrete and the continuum spectral regions, were obtained at the time-dependent density functional theory (TDDFT) level with dispersion correction. An analytic continuation procedure based on the Padé approximants was used in order to obtain the K-shell cross sections of the structures at the discrete and the continuum regions of the spectra. By examining the electronic spectra of water and ammonia bonded to coronene and circumcoronene, we observed that our results agree well with the experiments performed with graphene. This work provides a quantum mechanical interpretation to the NEXAFS experiments of water and ammonia adsorbed on graphene in terms of a physisorption model of these molecules by van der Waals forces.