DFT Functionals Research Articles

(Invited) Insight into Aqueous and Non-Aqueous Electrolyte Structure, Transport and Interfacial Properties from Molecular Modeling

Insight into Aqueous and Non-Aqueous Electrolyte Structure, Transport and Interfacial Properties from Molecular Modeling A molecular scale insight into ion transport and decomposition is important for understanding deficiencies of the currently used aqueous and non-aqueous electrolytes. In this presentation I will summarize progress made towards improving molecular scale understanding of the structure and electrochemistry for a wide range of aqueous and non-aqueous electrolytes. Modeling of non-aqueous electrolytes will focus on the competitive solvent and salt reduction at the passivated electrochemical interfaces using Born Oppenheimer Molecular Dynamics (BOMD) simulations using DFT functionals. These BOMD simulations included critical factors needed to realistically represent electrolyte reactivity at electrodes such as explicit description of the substrate – electrolyte interactions; accurate representation of electrolyte structure, ion pairing and aggregation near an electrode; and collection of sufficient statistics from multiple unique simulations that were initiated with differing initial configurations. For example, 20 BOMD simulations starting from different initial conditions using 2.0M LiPF6 in THF tetrahydrofuran/2-methyl tetrahydrofuran showed no solvent decomposition nor HF formation while only LiF formation was observed as a result of LiPF6 salt decomposition.1 The most frequently observed reduction events included a PF6 − coordinated to Li+ cations from the electrolyte and LiF surface that lead to anion defluorination and formation of 3LiF and PF3 gas. The solvent separated LiPF6 and did not actively participate in reduction. When surface defects in LiF were present near a high population of PF6 − the anions there was a preference for the LiPF6 reduction and repair the SEI without ether solvent decomposition. Interestingly, a number of fast diffusion events for F- from the electrolyte | LiF interface to the LiF-lithium metal interface was observed that would be expected to occur during Li stripping indicating that F- re-arrangement in the thin LiF passivation films should be also considered. 1 Electrolyte reduction at the passivated interfaces from these simulations will be contrasted with other solvents ranging from ethers with mixed salts or carbonates and results from the representative quantum chemistry (QC) calculations performed on the small model electrolyte clusters to estimate oxidation and reduction.In the second part of the presentation the non-reactive molecular dynamics (MD) using APPLE&P polarizable force field to examine bulk and interfacial properties of the lithium and zinc aqueous electrolytes and electrochemical interfaces with the focus on the transport mechanism and relative contribution to charge flux from the anions and cations.2 Combined together information from these modeling scales suggests numerous strategies for stabilizing the electrolyte – electrode interfaces for numerous aggressive high energy density cathodes combined coupled with graphite and metal anodes. References Chen, J.; Li, Q.; Pollard, T. P.; Fan, X.; Borodin, O.; Wang, C., Electrolyte design for Li metal-free Li batteries. Materials Today 2020.Borodin, O.; Self, J.; Persson, K. A.; Wang, C.; Xu, K., Uncharted Waters: Super-Concentrated Electrolytes. Joule 2020, 4 (1), 69-100.

Electronic energy gap closure and metal-insulator transition in dense liquid hydrogen

Using Quantum Monte Carlo (QMC) calculations, we investigate the insulator-metal transition observed in liquid hydrogen at high pressure. Below the critical temperature of the transition from the molecular to the atomic liquid, the fundamental electronic gap closure occurs abruptly, with a small discontinuity reflecting the weak first-order transition in the thermodynamic equation of state. Above the critical temperature, molecular dissociation sets in while the gap is still open. When the gap closes, the decay of the off-diagonal reduced density matrix shows that the liquid enters a gapless, but localized phase: there is a cross-over between the insulating and the metallic liquids. Compared to different DFT functionals, our QMC calculations provide larger values for the fundamental gap and the electronic density of states close to the band edges, indicating that optical properties from DFT potentially benefit from error cancellations.

Formation energy puzzle in intermetallic alloys: Random phase approximation fails to predict accurate formation energies

We performed density functional calculations to estimate the formation energies of intermetallic alloys. We used two semilocal approximations, the generalized gradient approximation (GGA) by Perdew-Burke-Ernzerhof (PBE) and the strongly constrained and appropriately normed (SCAN) meta-GGA. In addition, we utilized two nonlocal DFT functionals, the hybrid HSE06, and the state-of-the-art random phase approximation (RPA). The nonlocal functionals such as HSE06 and RPA yield accurate formation energies of binary alloys with completely-filled d-band metals, where semilocal functionals underperform. The accuracy at the nonlocal functionals is greatly reduced when a partially-filled d-band metal is present in an alloy, while PBE-GGA outperforms in these cases. We show that the accurate prediction of formation energies by any DFT method depends on its ability to predict the accurate electronic properties, e.g., valence d-band contribution to the density of states (DOS). The SCAN meta-GGA often corrects the PBE-DOS, however, it does not provide accurate formation energies compared to PBE. This is assumed to be due to the lack of proper error cancellation that should be expected due to the similar bulk nature of both alloys and their constituents, which may improve with the modification of meta-GGA ingredients. RPA yields too negative formation energies of alloys with partially-filled d-band metals. RPA results can be corrected by restoring the exchange-correlation kernel, thereby improving the short-range electron-electron correlation in metallic densities.

An improved seminumerical Coulomb and exchange algorithm for properties and excited states in modern density functional theory.

A seminumerical algorithm capable of performing large-scale (time-dependent) density functional theory (TD-DFT) calculations to extract excitation energies and other ground-state and excited-state properties is outlined. The algorithm uses seminumerical integral techniques for evaluating Coulomb and exchange parts for a set of density matrices as occurring in standard TD-DFT or similar methods for the evaluation of vibrational frequencies. A suitable optimized de-aliasing procedure is introduced. The latter does not depend on further auxiliary quantities and retains the symmetry of a given density matrix. The algorithm is self-contained and applicable to any orbital basis set available without the need for further auxiliary basis sets or optimized de-aliasing grids. Relativistic two-component excited-state TD-DFT calculations are reported for the first time using the developed seminumerical algorithm for standard and local hybrid density functional approximations. Errors are compared with the widely used "resolution of the identity" (RI) approximations for Coulomb (RI-J) and exchange integrals (RI-K). The fully seminumerical algorithm does not exhibit an enlarged error for standard DFT functionals compared to the RI approximation. For the more involved local hybrid functionals and within strong external fields, accuracy is even considerably improved.

Double-Hybrid DFT Functionals for the Condensed Phase: Gaussian and Plane Waves Implementation and Evaluation.

Intermolecular interactions play an important role for the understanding of catalysis, biochemistry and pharmacy. Double-hybrid density functionals (DHDFs) combine the proper treatment of short-range interactions of common density functionals with the correct description of long-range interactions of wave-function correlation methods. Up to now, there are only a few benchmark studies available examining the performance of DHDFs in condensed phase. We studied the performance of a small but diverse selection of DHDFs implemented within Gaussian and plane waves formalism on cohesive energies of four representative dispersion interaction dominated crystal structures. We found that the PWRB95 and B97X-2 functionals provide an excellent description of long-ranged interactions in solids. In addition, we identified numerical issues due to the extreme grid dependence of the underlying density functional for PWRB95. The basis set superposition error (BSSE) and convergence with respect to the super cell size are discussed for two different large basis sets.

Structural Stability of the CO2 @sI Hydrate: a Bottom-Up Quantum Chemistry Approach on the Guest-Cage and Inter-Cage Interactions.

Through reliable first-principles computations, we have demonstrated the impact of CO2 molecules enclathration on the stability of sI clathrate hydrates. Given the delicate balance between the interaction energy components (van der Waals, hydrogen bonds) present on such systems, we follow a systematic bottom-up approach starting from the individual 512 and 512 62 sI cages, up to all existing combinations of two-adjacent sI crystal cages to evaluate how such clathrate-like models perform on the evaluation of the guest-host and first-neighbors inter-cage effects, respectively. Interaction and binding energies of the CO2 occupation of the sI cages were computed using DF-MP2 and different DFT/DFT-D electronic structure methodologies. The performance of selected DFT functionals, together with various semi-classical dispersion corrections schemes, were validated by comparison with reference ab initio DF-MP2 data, as well as experimental data from x-ray and neutron diffraction studies available. Our investigation confirms that the inclusion of the CO2 in the cage/s is an energetically favorable process, with the CO2 molecule preferring to occupy the large 512 62 sI cages compared to the 512 ones. Further, the present results conclude on the rigidity of the water cages arrangements, showing the importance of the inter-cage couplings in the cluster models under study. In particular, the guest-cage interaction is the key factor for the preferential orientation of the captured CO2 molecules in the sI cages, while the inter-cage interactions seems to cause minor distortions with the CO2 guest neighbors interactions do not extending beyond the large 512 62 sI cages. Such findings on these clathrate-like model systems are in accord with experimental observations, drawing a direct relevance to the structural stability of CO2 @sI clathrates.

Halogen Bond of Halonium Ions: Benchmarking DFT Methods for the Description of NMR Chemical Shifts.

Because of their anisotropic electron distribution and electron deficiency, halonium ions are unusually strong halogen-bond donors that form strong and directional three-center, four-electron halogen bonds. These halogen bonds have received considerable attention owing to their applicability in supramolecular and synthetic chemistry and have been intensely studied using spectroscopic and crystallographic techniques over the past decade. Their computational treatment faces different challenges to those of conventional weak and neutral halogen bonds. Literature studies have used a variety of wave functions and DFT functionals for prediction of their geometries and NMR chemical shifts, however, without any systematic evaluation of the accuracy of these methods being available. In order to provide guidance for future studies, we present the assessment of the accuracy of 12 common DFT functionals along with the Hartree–Fock (HF) and the second-order Møller–Plesset perturbation theory (MP2) methods, selected from an initial set of 36 prescreened functionals, for the prediction of 1H, 13C, and 15N NMR chemical shifts of [N–X–N]+ halogen-bond complexes, where X = F, Cl, Br, and I. Using a benchmark set of 14 complexes, providing 170 high-quality experimental chemical shifts, we show that the choice of the DFT functional is more important than that of the basis set. The M06 functional in combination with the aug-cc-pVTZ basis set is demonstrated to provide the overall most accurate NMR chemical shifts, whereas LC-ωPBE, ωB97X-D, LC-TPSS, CAM-B3LYP, and B3LYP to show acceptable performance. Our results are expected to provide a guideline to facilitate future developments and applications of the [N–X–N]+ halogen bond.

A computational investigation of the equilibrium geometries, energetics, vibrational frequencies, infrared intensities and Raman activities of C2O y (y = 3, 4) species

Oligomers and co-oligomers of carbon oxides ( & ) hold considerable potential as high energy density materials (HEDMs) and are of prospective interest to astrochemists. Here, we theoretically investigate the equilibrium geometries, vibrational frequencies, infrared intensities, Raman activities, and energetics of several and species. Various DFT functionals were employed (BLYP, B3LYP, PBE, PBE0, ωB97X-D) along with Møller-Plesset methods (MP2, SCS-MP2) using the aug-cc-pVQZ basis set. Further calculations (excluding infrared intensities and Raman activities) were performed using Coupled-Cluster methods (CCSD, CCSD(T), CCSD) with the cc-pVTZ basis set. We discuss the accuracy and suitability of each method for predicting these properties alongside their capability to handle the multi-reference character of these species (through T1 diagnostic, largest T2 amplitudes, %TAE(T), ). The CCSD and SCS-MP2 approaches provide modest improvements in accuracy over their CCSD(T) and MP2 counterparts, while from the DFT functionals investigated, B3LYP strikes a balance between accuracy and computational cost. Heats of formation and bond dissociation energies were calculated using composite methods (G3MP2, CCCA-CCL, CCCA-S4). The dimer of symmetry was found to be the best HEDM candidate since its decomposition (to 2), is highly exothermic (by 260.93 kcal/mol at 298 K), alongside high estimated detonation velocities and pressures.

The active E4 structure of nitrogenase studied with different DFT functionals.

The present study concerns the technical aspects of obtaining the energetics for the E4 state of nitrogenase, the enzyme that fixes N2 in nature. EPR experiments have shown that the critical E4 structure that activates N2 should contain two bridging hydrides in the FeMo‐cofactor. It is furthermore in equilibrium with a structure where the two hydrides have been released and N2 binds. These observations led to the suggestion that E4 should have two bridging hydrides and two protonated sulfides. It is important to note that the structure for E4 has not been determined, but only suggested. For a long time, no DFT study led to the suggested structure, independent of which functional was used. However, in two recent DFT studies a good agreement with the experimental suggestion was claimed to have been obtained. In one of them the TPSS functional was used. That was the first out of 11 functionals tried that led to the experimentally suggested structure. In the second of the recent DFT studies, a similar conclusion was reached using the TPSSh functional. The conclusions in the recent studies have here been studied in detail, by calculating a critical energetic value strongly implied by the same EPR experiments. Both the TPSS and TPSSh functionals have been used. The present calculations suggest that those DFT functionals would not lead to agreement with the experimental EPR results either.

Can density functional theory ‘Cope’ with highly fluxional shapeshifting molecules?

Shape-shifting molecules such as bullvalene undergo rapid structural reorganizations via degenerate Cope rearrangements. Here, we obtain accurate CCSD(T)/CBS barrier heights and reaction energies for a wide range of Cope rearrangements in substituted bullvalenes (C10H9R, R = NH3, OH, CH3, H, F, Cl, SH, and CN). We use this benchmark dataset to evaluate the performance of DFT and ab initio methods for the kinetics and thermodynamics of these reactions. The reaction barrier heights pose a significant challenge for DFT methods – the best methods attain root-mean-square deviations of 4.9 (BMK), 4.5 (PBE0), 4.2 (PW6B95), and 3.8 (B1B95) kJ mol−1. Overall, only three DFT functionals (BMK, PW6B95, and MN12-SX) are able to surpass (or attain near) chemical accuracy for both barrier heights and reaction energies. In contrast, the double-hybrid DFT procedures ωB97X-2(LP), ωB97X-2(TQZ), PWPB95-D3, PBEQI-DH, and DSD-PBEB95-D3 give good-to-excellent performance.

Intermolecular C-H∙∙∙H-M dihydrogen bonds in five-membered heterocyclic complexes: a DFT and ab-initio study

In this work, dihydrogen bond between five-membered heterocyclic compounds (furan, thiophene, pyrrole, arsole, borole, phosphole, and silole) and alkali metal hydride HM (M = Li, Na, and K) were carried out by density functional theory and ab-initio calculations. A two pure (PBE, M06L) and four hybrids (B3LYP, B3P86, B3PW91, wB97XD) DFT functional and MP2 method with 6–311 + + G** basis set were used for five membered heterocyclic dihydrogen bond interactions. Molecular geometries, puckering parameters, energies, and natural bond orbital analysis of all the complexes were calculated by various DFT functionals and MP2 method. For all the complexes, smallest H∙∙∙H bond distance is observed for thiophene∙∙∙HK which has significant interaction energy (∆EC), while largest H∙∙∙H distance with smallest ∆EC is observed for pyrrole∙∙∙HLi complex. Among all the functionals, M06L predicted the smallest dihydrogen bond distances for all the complexes, while largest dihydrogen bond distance was observed by B3LYP functional. The infrared vibrational frequency analysis for all the complexes has revealed propensities in red and blue shift for the C–H and M–H bonds, respectively. Natural bond orbital and quantum theory of atom in molecules analyses were performed to examine the nature of interaction along with the molecular electrostatic potential which further confirm the existence of dihydrogen bonding.

NLOphoric imidazole-fused fluorescent anthraquinone dyes.

The Z-scan and DFT techniques were explored to investigate the non-linear optical properties of anthraquinone fused imidazole-based D-π-A dyes. With the help of UV-visible spectral analysis, pH study, CV analysis, HOMO-LUMO interaction, MEP plots, and quinoidal character the influence of intramolecular charge transfer characteristics and H-bonding process on electronic and photophysical studies of anthraquinone derivatives were understood. The dyes 2-(4-(diethylamino)-2-hydroxyphenyl)-3H-anthra[1,2-d]imidazole-6,11-dione (AQ1) and 2-(2-hydroxynaphthalen-1-yl)-1H-anthra[1,2-d]imidazole-6,11-dione (AQ2) displayed a single emission with pronounced Stokes shift and thermal stability (upto 290°C). The dye AQ1 exhibited strong charge transfer character which is explained by the ICT process leading to high nonlinear susceptibility χ(3) in AQ1 3.43×10-13 e.s.u relative to the dye AQ2 which has only ESIPT core. But, the dye AQ2 6.27Jcm-2 showed better optical limiting value. The NLO properties of AQ1 and AQ2 were computed by DFT functionals based on Hartree Fork (HF) percentage exchange. The dye AQ1 exhibits noticeable NLO properties. The global hybrid functionals with HF composition beyond 50% (BHHLYP, M06-HF) and the long rang corrected functionals (CAM-B3LYP, ωB97, and ωB97X) demonstrated comparable NLO properties relative to B3LYP and PBE0. It was observed that the combined effect of ICT and the H-bonding cores enhance the NLO properties. The experimental findings (Z-scan) were successfully correlated with theoretical (DFT) results.

The 1H and 13C chemical shifts of 5–5 lignin model dimers: An evaluation of DFT functionals

The calculations of 1H and 13C NMR chemical shifts were performed on three 5–5 lignin dimers, prominent substructures in softwood lignins, to compare with experimental data. Initially, 10 DFT functionals (B3LYP, B3PW91, BPV86, CAM-B3LYP, HCTH, HSEH1PBE, mPW1PW91, PBEPBE, TPSSTPSS, and ωB97XD) combined with the gage-including atomic orbital (GIAO) method and basic set 6–31G(d,p) were tested on 3,3′-(6,6′-dihydroxy-5,5′-dimethoxy-[1,1′-biphenyl]-3,3′-diyl)dipropionic acid (1), efficiently synthesized from ferulic acid. HSEH1PBE, mPW1PW91, and ωB97XD were found to be the three best performing functionals with strong correlations (r2 ≥ 0.9988) and low errors (CMAEs ≤ 0.0611 ppm for 1H and CMAEs ≤ 1.19 ppm for 13C). These functionals were also well-performed for the 1H and 13C shift calculations of dimers 3,3′-dimethoxy-5,5′-dimethyl-[1,1′-biphenyl]-2,2′-diol (2) and 5,5′-diallyl-3,3′-dimethoxy-[1,1′-biphenyl]-2,2′-diol (3). Overall, the ωB97XD functional consistently provided the calculated 1H and 13C chemical shifts with a high level of accuracy.

Ionization Energy and Reduction Potential in Ferrocene Derivatives: Comparison of Hybrid and Pure DFT Functionals.

Hybrid density functionals have been regularly applied in state-of-the-art computational models for predicting reduction potentials. Benchmark calculations of the absolute reduction potential of ferricenium/ferrocene couple, the IUPAC-proposed reference in nonaqueous solution, include the B3LYP/6-31G(d)/LanL2TZf protocol. We used this procedure to calculate ionization energies and reduction potentials for a comprehensive set of ferrocene derivatives. The protocol works very well for a number of derivatives. However, a significant discrepancy (>1 V) between experimental and calculated data was detected for selected cases. Three variables were assessed to detect an origin of the observed failure: density functional, basis set, and solvation model. It comes out that the Hartree-Fock exchange fraction in hybrid-DFT methods is the main source of the error. The accidental errors were observed for other hybrid models like PBE0, BHandHLYP, and M06-2X. Therefore, hybrid DFT methods should be used with caution, or pure functionals (BLYP or M06L) may be used instead.

A Systematic Study of DFT Performance for Geometry Optimizations of Ionic Liquid Clusters.

Clusters of two ion pairs of imidazolium-based ionic liquids were optimized with 43 different levels of theory, including DFT functionals and MP2-based methods combined with varying Dunning's basis sets, and added dispersion corrections. Better preforming DFT functionals were then applied to clusters consisting of four ion pairs. Excellent performance of some DFT functionals for the two ion pair clusters did not always match that of the four ion-paired clusters despite interionic distances remaining constant between the optimized two and four ion-paired clusters of the same ionic liquid. Combinations of DFT functional and basis set such as ωB97X-D/cc-pVDZ, M06-2X/aug-cc-pVDZ, B3LYP-D3/cc-pVTZ, and TPSS-D3/cc-pVTZ gave excellent results for geometry optimization of two ion-paired clusters of imidazolium ionic liquids but gave larger deviations when applied to the four ion-paired clusters of varying ionic liquids. Empirical dispersion corrections were seen to be crucial in correctly capturing correlation effects in the studied ionic liquid clusters, becoming more important in larger clusters. Dunning's double-ζ basis set, cc-pVDZ, is associated with the smallest root mean squared deviations for geometries; however, it also produces the largest deviations in total electronic energies. ωB97X-D and M06-2X produced the best performance with the augmented version of this basis set. The triple-ζ basis set, cc-pVTZ, leads to the best performance of most of the DFT functionals (especially the dispersion-corrected ones) used, whereas its augmented version, aug-cc-pVTZ, was not seen to improve results. The combinations of functional and basis set that gave the best geometry and energetics in both two and four ion-paired clusters were PBE-D3/cc-pVTZ, ωB97X-D/aug-cc-pVDZ, and BLYP-D3/cc-pVTZ. All three combinations are recommended for geometry optimizations of larger clusters of ionic liquids. PBE-D3/cc-pVTZ performed the best with an average deviation of 2.3 kJ mol-1 and a standard deviation of 3.4 kJ mol-1 for total electronic energy when applied to four ion-paired clusters. Geometries optimized with FMO2-SRS-MP2/cc-pVTZ produced total energy within 2.0 kJ mol-1 off the benchmark in two ion-paired clusters, with the cc-pVDZ basis set performing unsurprisingly poorly with the same method. The error increased to 4.8 kJ mol-1 on average in four ion-paired clusters, with the smallest RMSD deviations in geometries when compared to the benchmark ones. This study is the first report that investigated the performance of DFT functionals for two and four ion-paired clusters of a wide range of ionic liquids consisting of commonly used cations such as pyrrolidinium, imidazolium, pyridinium, and ammonium. It also identified the importance of assessing the performance of quantum chemical methods for ionic liquids on a variety of cation-anion combinations.

Combined Spectroscopic and TD-DFT Analysis to Elucidate Substituent and Acidochromic Effects in Organic Dyes: A Case Study on Amino- versus Nitro-Substituted 2,4-Diphenylquinolines.

A combined spectroscopic and TD-DFT case study was performed, to identify a robust method to calculate the complex near UV/Vis absorption spectra of various amino- vs. nitro-substituted 2,4-diphenylquinolines, which vary strongly under neutral and successively acidic conditions. For this, different DFT functionals were tested for geometry optimization and the TD part to calculate the neutral and different protonated species in a fast screening approach, i. e. using single point calculations in an implicit solvent. Offset-corrected M06HF, hitherto only applied to polymers, was identified as a suitable method to reproduce the absorption spectra in a reasonable fashion for all different substitution pattern and all different protonated species at different pH values; moreover, the method properly predicts the energetic ordering of low-lying n-π* and ππ* transitions, which is decisive for the non-/emissive nature of the different compounds. In all, this might provide a valuable tool for computer-aided design of related classes of compounds.

Synthesis, NMR, Raman, thermal and nonlinear optical properties of dicationic ionic liquids from experimental and theoretical studies

Two new di-cationic imidazolium based ionic liquids (ILs) containing chloride, (bisImCl), or hexafluorophosphate anions (bisImPF6) have been synthesized and characterized by FT-Raman and 1H- and 13C NMR spectroscopies. The p-xylyl group acts a spacer between two imidazolium rings in the cation. The influence of the anions on thermal properties of the compounds has been investigated. Both bisImCl and bisImPF6 have shown good thermal stability up to at least 280 °C. Intermolecular and cation-anion interactions have been investigated by NMR spectroscopy. B3LYP/6-311++G∗∗ calculations have optimized the structure of bisIm cation with both anions. Both Cl are found to be in a monodentate coordination, while in bisImPF6 only one PF6 group presents monodentate coordination. AIM calculations at the same level of theory have evidenced a higher number of interactions in bisImPF6, as compared to bisImCl. A complete assignment of the vibrational frequencies for the cation, bisImCl and bisImPF6 are here reported together with a set of harmonic scaled force constants calculated for the cation and bisImCl. Further, polarizability (α) and the static first hyperpolarizabilities (β) of these ILs are calculated by different DFT functionals in order to understand nonlinear optical (NLO) properties. It is observed an inverse correlation between the predicted β value and the HOMO-LUMO energy difference (Δε) from two state models. The high gap value observed for bisImPF6 justifies its low reactivity, as supported by the high number of interactions predicted for this ionic liquid.

Ab initio description of nanodiamonds: A DFT and TDDFT benchmark

In this article 15 DFT functionals were evaluated in order to find a good description of the electronic features and geometries of the nanodiamonds. With this in mind, two sets of molecules were designed, one of them composed by well-known organic molecules and other by diamondoids. The main parameters considered for comparison in this work are the excitation energies, ionization potentials, and the energies of the frontier orbitals. Moreover, absorption distances and binding energies were also considered to assess the quality of the description of the physisorption process. The best overall performance was found on hybrid functionals and more specifically on those with low HF percentage (TPSSH and O3LYP), despite reasonable results with lower computational cost can be obtained with GGA or LDA methods. The use of a correction for the dispersion interaction is mandatory except when a Truhlar functional, LDA or ωB97X functional is used. An augmented triple zeta basis set is recommended, especially for the description of the nanodiamond model, while an augmented double zeta is enough to yield a converged geometry.

DFT and TDDFT Study of 4-((Furan-2-Ylmethyl)Sulfonyl)-Substituted ZINC(II) Phthalocyanine: Importance of Grimme Dispersion with A Becke–Johnson Damping Correction and the Substituent Effect

In this work, we report a theoretical study on the structural, vibrational, and electronic properties of 4-((furan-2-ylmethyl)sulfonyl)-substituted zinc(II) phthalocyanine. We start to study the performance of DFT functionals for the unsubstituted systems using the B97D3, B3LYP, M06-2X, PBE1PBE, and BMK functionals. The B97D3 functional with a dispersion correction is in good agreement with the theoretical and experimental results, which suggests that the D3 dispersion plays an essential role in the study of different properties of zinc phthalocyanine. Using the B97D3 functional with def2 TZVP for Zn and 6-311+G(d,p) for the other atoms, we determine the structural, vibrational, and electronic properties of 4-((furan-2-ylmethyl)sulfonyl)-substituted zinc(II) phthalocyanine. We notice that the HOMO is localized on both substituent and zinc(II) phthalocyanine but the LUMO is the same as in the unsubstituted compound. This demonstrates a higher absorption wavelength in agreement with the experimental results of this substituted system.

Encapsulation of Hydrogen Molecules in C50 Fullerene: An ab Initio Study of Structural, Energetic, and Electronic Properties of H2@C50 and 2H2@C50 Complexes.

Various DFT functionals, including those containing long-range interactions and dispersion, together with HF and MP2 theoretical methods, were used to identify the number of H2 molecules that can be encapsulated inside a C50 cage. It is demonstrated that the 2H2@C50 complex is thermodynamically unstable based on its positive complexation energy. Some discrepancies, however, were found with respect to the stability of the H2@C50 complex. Indeed, SVWN5, PBEPBE, MP2, B2PLYP, and B2PLYPD calculations confirmed that the H2@C50 complex is thermodynamically stable, while HF, BP86, B3LYP, BHandHLYP, LC–wPBE, CAM–B3LYP, and wB97XD showed that this complex is thermodynamically unstable. Nevertheless, examination of strain and dispersion energies further supported the fact that one H2 molecule can indeed be encapsulated inside the C50 cage. Other factors, such as the host–guest interactions and bond dissociation energy, were analyzed and discussed.