Comprehensive Ab Initio Calculations Research Articles

Neutral 2-phenylbenzimidazole-based iridium(III) complexes with picolinate ancillary ligand: tuning the emission properties by manipulating the substituent on the benzimidazole ring.

We report the synthesis and characterization of ten neutral bisheteroleptic iridium(III) complexes with 2-phenylbenzimidazole cyclometallating ligand and picolinate as ancillary ligand. The 2-phenylbenzimidazole has been modified by selected substituents introduced on the cyclometallating ring and/or on the benzimidazole moiety. The integrity of the complexes has been assessed by NMR spectroscopy, by high-resolution mass spectrometry and by elemental analysis. The complexes are demonstrated to be highly phosphorescent at room temperature and a luminescence study with comprehensive ab initio calculations allow us to determine the lowest emitting excited state which depends on the substituent nature and its position on the cyclometallating ligand.

Doping-mediated excited state dynamics of diphosphine-protected M@Au12 (M = Au, Ir) superatom nanoclusters.

Doping heterometal atoms into ligand-protected gold superatom nanoclusters (Aun NCs) is proposed to further diversify their geometrical and electronic structures and enhance their photoluminescence properties, which is attributed to the mixing and effects between atoms. However, the fundamental principles that govern the optoelectronic properties of the doped Aun NCs remain elusive. Herein, we systematically explored two prototypical 8-electron Aun (n = 11 and 13) NCs with and without Ir dopant atoms using comprehensive ab initio calculations and real-time nonadiabatic molecular dynamics simulations. These doped Aun NCs maintain their parent geometrical structures and 8-electron superatomic configuration (1S21P6). Strong core-shell (Ir-Aun) electronic coupling significantly expands the energy gap, resulting in a weak nonadiabatic coupling matrix element, which in turn increases the carrier lifetime. This increase is mainly governed by the low-frequency vibration mode. We uncovered the relationship between electronic structures, electron-vibration, and carrier dynamics for these doped Aun NCs. These calculated results provide crucial insights for the atomically precise design of metal NCs with superior optoelectronic properties.

A comprehensive investigation of Ag7P3X11 (X = {O, S, and Se}) solid-state silver superionic conductors

This investigation rigorously analyzes and introduces a new class of high-performance inorganic solid-state electrolytes, formulated as Ag7P3X11 (X = {O, S, Se}), through comprehensive ab initio calculations, highlighting their potential for advanced energy storage technologies.

Solar driven CO2 hydrogenation to HCOOH on (TiO2)n (n = 1-6) atomic clusters.

Artificial photosynthesis is a crucial reaction that addresses energy and environmental challenges by converting CO2 into fuels and value-added chemicals. However, efficient catalytic activity using earth-abundant materials can be challenging due to intrinsic limitations. Herein, we explore neutral (TiO2)n (n = 1-6) atomic clusters for CO2 hydrogenation via comprehensive ab initio calculations combined with time-dependent functional theory. Our results show that these (TiO2)n clusters exhibit outstanding thermodynamic stabilities and decent surficial activities for CO2 activation and H2 dissociation, both of which possess kinetic barriers down to 0-0.74 eV. We establish a relationship between the binding strength of *CO2 species and electron characterization for these (TiO2)n clusters. These clusters, which have a wide energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccpied molecular orbital (LUMO) that allows them to harvest the solar light in the ultraviolet regime, enabling efficient catalysis for driving the catalysis of CO2 conversion. They provide exclusive reaction channels and high selectivity for yielding HCOOH products via the carboxyl mechanism, involving the kinetic barrier of the limiting step of 0.74-1.25 eV. We also investigated the substrate effect on supported (TiO2)n clusters, with non-metallic substrates featuring inert surfaces serving as suitable options for anchoring (TiO2)n clusters while preserving their intrinsic activity and selectivity. These computational results have significant implications not only for meeting energy demands but also for mitigating carbon emissions by utilizing CO2 as an alternative feedstock rather than considering it solely as a greenhouse gas.

Engineering coexistence between free and trapped carriers via extrinsic polarons

The transition between delocalized and localized electronic configurations is a characteristic property of all small-polaron systems. In this study, we explore a doping approach by which the coexistence between delocalized and localized electronic states may be precisely tuned within extrinsic polaron systems. Through comprehensive ab initio calculations employing hybrid functionals, for which Ti-doped ${\mathrm{SnO}}_{2}$ is selected as a model system, it is demonstrated how strain and alloying can be utilized to achieve a high degree of control over the activation energetics separating localized and delocalized electronic states. By means of a phenomenological tight-binding analysis of our ab initio results, it is shown that two physical parameters play a dominant role in the associated transition physics: (1) the dopant electronic offset ${\mathrm{\ensuremath{\Delta}}}_{a}$, and (2) the dopant bandwidth $W$. Overall, this study presents an exciting route toward tailoring the coexistence between delocalized and localized states with a potentially much greater degree of control than is currently possible in intrinsic materials.

Robust Dirac spin gapless semiconductors in a two-dimensional oxalate based organic honeycomb-kagome lattice.

Two-dimensional (2D) ferromagnetic materials with intrinsic and robust spin-polarized Dirac cones are of great interest in exploring exciting physics and in realizing spintronic devices. Using comprehensive ab initio calculations, herein we reveal a family of 2D oxalate-based metal-organic frameworks (MOFs) that possess the desired characteristics. We propose that these 2D oxalate-based MOFs may be assembled by oxalate ions (C2O42-) and two homo-transition metal atoms. We demonstrate that 2D MOFs of Ni2(C2O4)3 and Re2(C2O4)3 are intrinsic Dirac spin gapless semiconductors with linear band dispersion, low energy dissipation and high electron carrier velocity. As robust ferromagnets, they also possess large magnetic moments, large perpendicular magnetic anisotropy, and high Curie temperatures, e.g. 208 K for Ni2(C2O4)3. In particular, spin-orbit coupling triggers a topologically nontrivial band gap of 143 meV in Re2(C2O4)3, which is promising to realize the quantum anomalous Hall effect at high temperatures.

Comprehensive ab-initio calculations of AlNiX (X = P, As and Sb) half-Heusler compounds: Stabilities and applications as green energy resources

The objective of this work is to explore structural, mechanical and thermal stability including electronic, optical and thermoelectric properties of state-of-the-art AlNiX (X = P, As and Sb) half-Heusler compounds having 18 valence electron count (VEC). Calculations have been carried out in the framework of density functional theory (DFT) implemented in WIEN2k code followed by the solution of the Boltzmann transport equation with constant relaxation time approximation. In the most energetically favorable structure, their lattice constants lie in the range of 5.501 Å – 5.983 Å and band gaps have been found to be 0 eV, which confirm the metallic behavior of these compounds. The different elastic and thermodynamic parameters confirm their mechanical and thermal stability with a mechanically anisotropic and ductile nature. Specific heat and entropy of these materials increase as the atomic number of X atom increases. The calculated optical parameters prove their candidature for promising photovoltaic devices and shields for UV radiation. The thermal conductivity has been computed using Slack's model. This detailed study shows that these compounds are promising for materials scientists due to their very high lattice thermal conductivity and low figure of merit. We deny recommending them as good thermoelectric applications.

Solar driven CO2 hydrogenation on transition metal doped Zn12O12 cluster.

Photocatalytic hydrogenation of carbon dioxide (CO2) to produce value-added chemicals and fuel products is a critical routine to solve environmental issues. However, developing photocatalysts composed of earth-abundant, economic, and environmental-friendly elements is desired and challenging. Metal oxide clusters of subnanometer size have prominent advantages for photocatalysis due to their natural resistance to oxidation as well as tunable electronic and optical properties. Here, we exploit 3d transition metal substitutionally doped Zn12O12 clusters for CO2 hydrogenation under ultraviolet light. By comprehensive ab initio calculations, the effect of the dopant element on the catalytic behavior of Zn12O12 clusters is clearly revealed. The high activity for CO2 hydrogenation originates from the distinct electronic states and charge transfer from transition metal dopants. The key parameters governing the activity and selectivity, including the d orbital center of TM dopants and the energy level of the highest occupied molecular orbital for the doped Zn12O12 clusters, are thoroughly analyzed to establish an explicit electronic structure-activity relationship. These results provide valuable guidelines not only for tailoring the catalytic performance of subnanometer metal oxide clusters at atomic precision but also for rationally designing non-precious metal photocatalysts for CO2 hydrogenation.

Immobilized trimeric metal clusters: A family of the smallest catalysts for selective CO2 reduction toward multi-carbon products

Abstract Using clean electricity to convert carbon dioxide (CO2), an earth abundant carbon feedstock, to high-energy fuels is a fascinating energy strategy for a sustainable future. However, high yield of multi-carbon products remains a grand challenge. Herein, we show that trimeric metal clusters anchored on nitrogen doped porous carbon materials possess remarkable activity and selectivity for C2–C3 hydrocarbons and alcohols. By comprehensive ab initio calculations on 3d, 4d and 5d transition metal trimers, we for the first time illuminate their specialty for catalyzing this tough reaction. These spatially confined triatomic metal centers are capable of simultaneous fixation of plural CO2 molecules, provide exclusive reaction channels that sterically and electronically facilitate C–C coupling, and have tunable selectivity by mediating the cluster-substrate interaction. The catalytic mechanism and structure-activity relationship are uncovered for these sub-nano clusters with robust stability. These results provide important knowledge for atomically precise design of novel catalysts for direct conversion of CO2 to high-energy fuels and high-value chemicals.

Magnetic and Electronic Properties of β-Graphyne Doped with Rare-Earth Atoms**Supported by the Scientific Research Plan Projects of Shannxi Education Department under Grant No 17JK0366, and the Natural Science Foundation of Shaanxi Science and Technology Department under Grant Nos 2018JQ1042, 2017ZDXM-GY-114 and 2018GY-044.

Structural, electronic and magnetic properties of La-, Ce-, Pr-, Nd-, Pm-, Sm- and Eu-doped β-graphyne are investigated by comprehensive ab initio calculation based on density functional theory. The adsorption energies indicate that the dopings are suitable. The doped β-graphyne undergoes transition from semiconductor to metal. Furthermore, the doping of Nd, Pm, Sm and Eu atoms can induce magnetization. The results are useful for spintronics and the design of future electronic devices.

Silicon Nanocages for Selective Carbon Dioxide Conversion under Visible Light

Artificial photosynthesis for CO2 conversion to fuels and value-added chemicals is a tactic to close the anthropogenic carbon cycle. To this end, developing efficient catalysts composed of earth-abundant, economic, and eco-friendly elements is desirable but challenging. By comprehensive ab initio calculations, we show for the first time that caged silicon clusters doped by vanadium atom (VSin, n = 12–15) can catalyze CO2 hydrogenation to various C1 products (i.e., carbon monoxide, formic acid, formaldehyde, methanol, and methane) with kinetic barriers down to 0.67–1.53 eV and selectivity uniquely determined by cluster size and geometry. These clusters, which can be produced in laboratory with good stability, have suitable energy gap and can absorb sunlight from the visible to ultraviolet regime for driving the catalysis. Hence, these metal-doped Si clusters form a potential family of photocatalysts for selective CO2 hydrogenation. Their superior catalytic activity stems from the unsaturated states of the Si cage, which are mediated by sp-d hybridization and V–Si charge transfer. The CO2 adsorption strength is correlated with the coordination number and p orbital center of Si atoms. Such geometry–electronic structure–activity correlation should be applicable to the atomically precise design of novel silicon-based nanocatalysts for various renewable energy applications.

Inner edge magnetisms in carbon honeycombs

We show by comprehensive ab initio calculations that sp2 carbon honeycombs recently synthesised by Krainyukova et al. [Phys. Rev. Lett. 116, 055501 (2016)] exhibit antiferromagnetism, not only at the inner edge of the zigzag ribbon component but also at the chain of sp2 carbon that joins three zigzag ribbons. The π antiferromagnetism at the joint chain has spin orientations that alternatively change along the axis and stems from a super-exchange mechanism. Along with the spin-polarization, the joint chain conduction channel opens an energy gap. The spin-polarization of the zigzag edge due to the magnetic instability of the localized edge states is less stable in energy. Through hole doping, the zigzag edge antiferromagnetism is enhanced and stabilized as the magnetic ground state, along with the re-opening of the joint chain conduction channel. When the carbon honeycombs are reconstructed into sp3-sp2 hybrid honeycombs, the π states of the joint are diminished, but the zigzag edge magnetism is preserved. Our results propose carbon honeycombs as novel magnetic carbon with competing polarization configurations.

Novel photocatalytic water splitting solar-to-hydrogen energy conversion: CdLa2S4 and CdLa2Se4 ternary semiconductor compounds.

Comprehensive ab initio calculations from first- to second-principles methods are performed to investigate the suitability of non-centro-symmetric CdLa2S4 and CdLa2Se4 to be used as active photocatalysts under visible light illumination. The calculations reveal the direct band gap nature of both compounds with large absorption coefficients (104-105 cm-1). The absorption edges of CdLa2S4 and CdLa2Se4 occur at λ = 579.3 nm and λ = 670.1 nm, and the optical band gaps are estimated to be 2.14 eV and 1.85 eV for CdLa2S4 and CdLa2Se4, respectively. These gaps are larger than 1.23 eV the required optical band gap for photocatalytic performance to split water under visible light illumination. The calculated potentials of the conduction band and the valence band edges indicate that CdLa2S4 and CdLa2Se4 have strong reducing powers for H2 production. The obtained results reveal that the high photogenerated carrier mobility favors enhancement of the photocatalytic performance. It has been found that there is a large mobility difference between the electrons (e-) and the holes (h+), which is useful for the separation of e- and h+, reduction of e- and h+ recombination rate, and improvement of the photocatalytic activity. Based on these findings, one can conclude that CdLa2S4 and CdLa2Se4 satisfied all requirements to be efficient photocatalysts. This will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new photocatalysts with good photocatalytic performances.

Conformational stability, spectroscopic and computational studies, HOMO–LUMO, NBO, ESP analysis, thermodynamic parameters of natural bioactive compound with anticancer potential of 2-(hydroxymethyl)anthraquinone

Natural product drugs play a dominant role in pharmaceutical care. Nature is an attractive source of new therapeutic candidate compounds as a tremendous chemical diversity is found in millions of species of plants, animals, marine organism and micro-organism. A antifungal activity against important opportunist micro-organism and against those involved in superficial mycosis, all from nosocomial origin. The acute in vitro cytotoxicity evaluation of each anthraquinone (AQ) isolated from these bioactive extracts, on a mammalian eukaryotic cell line (Vero cells), allowed us to establish the non-cytotoxic concentration range, which was used to evaluate the anti-microbial effect. A comprehensive ab initio calculation using the DFT/6-31+G(d) level theory showed that 2-(hydroxymethyl)anthraquinone can exist in four possible conformations, which can interchange through the OH group on the five-membered ring. Density functional theory calculations were used to predict the vibrational frequencies and to help in normal mode, assignments. Furthermore, a natural bond orbital analysis was performed describing each hydrogen bond as donor accepter interaction. The Fourier transform infrared spectra (4000–400cm−1) and the Fourier transform Raman spectra (3500–100cm−1) of the HMA in the solid space have been recorded. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The calculated ESP contour map shows the electrophilic and nucleophilic region of the molecule.

Interpretation of the Gas-Phase Solvent Deuterium Kinetic Isotope Effects in the SN2 Reaction Mechanism: Comparison of Theoretical and Experimental Results in the Reaction of Microsolvated Fluoride Ions with Methyl Halides

We carried out a comprehensive ab initio calculation and transition-state theory analysis of the solvent and secondary deuterium kinetic isotope effects in the SN2 reactions of microsolvated fluoride ions with methyl halides. Water, methanol, and hydrogen fluoride were used as solvents, and the results are compared with recent experiments. Kinetic isotope effects were dissected into contributions from translations, rotations, and different vibration modes, and the validity of such analysis is also discussed. Excellent agreement was found for some reactions, whereas the agreement was poor for other reactions. We showed that the deviation between theory and experiments is related to the reaction kinetics; a faster reaction produced a kinetic isotope effect that was systematically larger (less inverse) than the calculated value. In addition, we also found that the magnitude of the deviation is proportional to the reaction efficiency. We rationalize the disagreement as a failure of the transition-state theory to model barrierless reactions, and we propose a very simple scheme to interpret these findings and predict the deviation between experimental and theoretical values in those reactions.

Spectroscopic and Computational Studies of the Intramolecular Hydrogen Bonding of 2-Indanol

2-Indanol in its most stable form is stabilized by internal hydrogen bonding, which exists between the hydroxyl hydrogen atom and the pi-cloud of the benzene ring. A comprehensive ab initio calculation using the MP2/cc-pVTZ level of theory showed that 2-indanol can exist in four possible conformations, which can interchange through the ring-puckering vibration and the internal rotation of the OH group on the five-membered ring. A potential energy surface in terms of these two vibrational coordinates was calculated. Density functional theory calculations were used to predict the vibrational frequencies and to help in normal mode assignments. Fluorescence excitation spectra of 2-indanol confirm the presence of the four conformers in the electronic ground and excited states. The spectral intensities indicate that, at 90 degrees C, 82% of the molecules exist in its most stable form with the intramolecular hydrogen bonding. The other isomers are present at approximately 11, 5, and 3%. The MP2/6-311++G(d,p) calculation predicts a distribution of 70, 13, 9, and 8% at 90 degrees C, the experimental sample temperature.

Cis-Diamminodichloronickel and Its Interaction With Guanine and Guanine-Cytosine Base Pair

Comprehensive ab initio calculations are performed on cis-diamminodichloronickel (cisni) at the HF, DFT, and MP2 levels of theory. The results are compared to those obtained for cisplatin. The characteristics of the interactions of cisni with guanine (G) and guanine–cytosine (GC) base pair are also evaluated and compared to the interactions of cisplatin. Cisni causes similar geometric changes of the base as cis-platinum when complexed to guanine. The nickel, palladium and platinum complexes also show similar characteristics when complexed to GC base pair. However, this study predicts higher dissociation energy of the cisni chlorine ligands that indicate areas of differences between the title Ni and Pt and Pd complexes. Comparison of the G-cisni interaction energy to that of cisplatin and cispd indicate differences between the Ni and Pd complexes, but also reveals its closer similarities to cisplatin.

Water dimer to pentamer with an excess electron: Ab initio study

We have studied the electronic structures, energetics, electron vertical detachment energies (VDEs), and O–H vibrational spectra of various conformers of water clusters with an excess electron [e+(H2O)n, n=2–5] or anionic water clusters [(H2O)n−] using comprehensive ab initio calculations. As noted in our preliminary work [J. Kim et al., Phys. Rev. A 59, 930 (1999)], the structure of the water dimer anion is characterized to be linear-like (slightly towards the cis conformer) but very floppy with large wide-ranging zero point vibration motion at 0 K. The lowest energy structures of the water trimer to pentamer anion are all cyclic with very small VDEs (< 0.05 eV). However, these cyclic structures which are metastable are prone to become the neutral species by releasing an excess electron because the transition barriers seem to be very small. Thus, observation of such cyclic structures would not be feasible. On the other hand, a linear water trimer structure which is 0.8 kcal/mol higher in energy than the cyclic form gives the VDE (0.14 eV) close to the experimentally observed value. A large VDE observed in the pentamer also corresponds to a slightly high energy conformer. This suggests that formation of anionic water clusters in experiments seems to be dynamically and kinetically driven.

Stability and Three-Dimensional Aromaticity of closo-Monocarbaborane Anions, CB(n)()(-)(1)H(n)(-), and closo-Dicarboranes, C(2)B(n)()(-)(2)H(n)().

Comprehensive ab initio calculations RMP2(fc)/6-31G on the closo-monocarbaboranes, CB(n)()(-)(1)H(n)()(-) (n = 5-12), and the closo-dicarboranes, C(2)B(n)()(-)(2)H(n)() (n = 5-12), show that the relative energies of all the positional isomers agree with the qualitative connectivity considerations of Williams and with the topological charge stabilization rule of Gimarc. The reaction energies (DeltaH) of the most stable positional isomers, 1-CB(4)H(5)(-), CB(5)H(6)(-), 2-CB(6)H(7)(-), 1-CB(7)H(8)(-), 5-CB(8)H(9)(-), 1-CB(9)H(10)(-), 2-CB(10)H(11)(-), CB(11)H(12)(-), as well as 1,5-C(2)B(3)H(5), 1,6-C(2)B(4)H(6), 2,4-C(2)B(5)H(7), 1,7-C(2)B(6)H(8), 4,5-C(2)B(7)H(9), 1,10-C(2)B(8)H(10), 2,3-C(2)B(9)H(11), and 1,12-C(2)B(10)H(12) (computed using the equations, CBH(2)(-) + (n - 1)BH(increment) --> CB(n)()H(n)()(+1)(-) (n = 4-11) and C(2)H(2) + nBH(increment) --> C(2)B(n)()H(n)()(+2) (n = 3-10)), show that the stabilities of closo-CB(n)()(-)(1)H(n)()(-) and of closo-C(2)B(n)()(-)(2)H(n)() generally increase with increasing cluster size from 5 to 12 vertexes. This is a characteristic of three-dimensional aromaticity. There are variations in stabilities of individual closo-CB(n)()(-)(1)H(n)()(-) and closo-C(2)B(n)()(-)(2)H(n)() species, but these show quite similar trends. Moreover, there is rough additivity for each carbon replacement. The rather large nucleus independent chemical shifts (NICS) and the magnetic susceptibilities (chi), which correspond well with one another, also show all closo-CB(n)()(-)(1)H(n)()(-) and closo-C(2)B(n)()(-)(2)H(n)() species to exhibit "three-dimensional aromaticity". However, the aromaticity ordering based on these magnetic properties does not always agree with the relative stabilities of positional isomers of the same cluster, when other effects such as connectivity and charge considerations are important.