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 Theoretical Chemistry AccountsJournal Prestige (SJR): 0.564 Citation Impact (citeScore): 1Number of Followers: 6      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1432-881X - ISSN (Online) 1432-2234 Published by Springer-Verlag  [2469 journals]
• Mechanism of oxygen reduction reaction on Ni/CNTs and Ni/X-CNTs (X=B, N,
O) catalysts: a theoretical study

Abstract: Abstract Fuel cell is an emerging technology for energy conservation and environmental protection, with simple structure and high energy conversion efficiency. However, the kinetics of cathode ORR is slow. Therefore, high-performance, highly selective catalysts are urgently needed. This work aims to use the DFT to conduct structural design and performance optimization of Ni/CNTs and Ni/X-CNTs (X=B, N, O) catalysts. Studies showed that the number of Ni atom loading, the number and types of doping of heteroatoms all affected the activity of catalysts to some extent. The adsorption energy of O2 was calculated to determine that O2 was adsorbed on Ni(6)/B(2)-CNTs in the Bridge mode. Meanwhile, the comparative analysis of 2 e− path and 4 e− path indicated that ORR occurred in Ni(6)/B(2)-CNTs in acidic medium was more inclined to follow the 4 e− path. The present work has some reference and value for specific experiments.
PubDate: 2022-05-17

• A theoretical investigation of the regio- and stereoselectivities of the
[3 + 2] cycloaddition reaction between ethyl vinyl ether and
substituted α-alkoxynitrones

Abstract: Abstract The observed regioselectivity in [3 + 2] cycloaddition reactions (32CA) between ethyl vinyl ether (2) and substituted α-alkoxynitrones (1a, 1b) was studied theoretically using the conceptual density functional theory (CDFT) method at B3LYP/6–31 +  + G(d, p) computational level. The regioselectivity and stereoselectivity of this 32CA reaction are rationalized by computations of activation energy calculations, Fukui FMO analysis, and local reactivity indices derived from CDFT in both the ground and transitions states. Analysis of the Fukui and CDFT indices allows the recognition of the nitrones as TACs participating in zwitterionic zw-type 32CA polar reactions and highly dependent on the electrophilic/nucleophilic character of the reactants. Thermodynamic and kinetic parameters of the putative ortho/meta species were determined to describe the preferred regioisomer. The TS obtained results suggest that the reactions proceed via a one-step mechanism that preferentially leads to the ortho-exo stereoisomer over the endo one. Both electronic and steric effects affect the stereoselectivity of these reactions. The results show that the experimental trends in the relative reactivity and regioselectivity of these reactions are correctly predicted using the computational CDFT method.
PubDate: 2022-04-16

• A DFT study of the tautomerism of 1H-benzo[de]cinnolines and their
protonated forms

Abstract: Abstract 1H-Benzo[de]cinnolines and 1H-indeno[6,7,1-def]cinnolines have been studied theoretically at the B3LYP/6-311++G(d,p) level in the gas-phase and in water solution (PCM model); gas-phase geometries were used to calculate absolute shieldings (GIAO) that were transformed into chemical shifts using empirical equations. The annular tautomerism of neutral species and of protonated cations have been determined, and the most stable cations coincide with those determined experimentally.
PubDate: 2022-04-11

• B6C8 and its anion: a planar dodecagon reinforced by the central strong
B−B single bond and aromaticity

Abstract: Abstract A quantum chemical calculation was performed to investigate the structural and bonding properties of B6C8− anion and B6C8 neutral. The geometries of the most stable isomers of both B6C8− anion and B6C8 neutral were found to be a planar dodecagon with four C2 units separated by four B atoms, which can be further reinforced by the central strong B−B single bond and aromaticity. The bond lengths, Wiberg bond orders, constant charge density surfaces, MOs, and AdNDP analyses were used to give insight into the chemical bonds in the C2h symmetric planar dodecagon of B6C8 neutral. The results showed that the most stable isomer of B6C8 has a closed-shell electronic structure with HOMO–LUMO gap of 2.20 eV and has σ plus π double delocalized bonding characters. More interestingly, the most stable isomer of B6C8 exhibits σ aromaticity and π antiaromaticity.
PubDate: 2022-04-11

• Rationalizing the catalytic performance of Cr(III) complexes stabilized
with alkylphosphanyl PNP ligands for selective ethylene
tri-/tetramerization: a DFT study

Abstract: Abstract The effect of alkylphosphanyl substitutions on the PNP scaffold toward ethylene tri-/tetramerization has been explained using density functional theory (DFT). Our calculations show that different alkylphosphanyl substitutions considerably influence the catalytic environment and thus affect the catalytic performance of alkylphosphanyl PNP/Cr system. Comparing the rate-determining steps (RDSs) of all precatalysts 1–9, we have rationalized the product selectivity. The reactivity of precatalysts 5–6 {Ph2PN(cyclopentyl)PR2, 5, R = Et; 6, R = iPr} based systems was rationalized by frontier orbital theory. In addition, we further calculated the cyclic by-product paths of precatalysts 5–6 based systems, and the results show that the precatalyst 6 based system offers a high energy barrier toward the formation of cyclic C6 by-products and therefore produce a small amount of these products.
PubDate: 2022-04-10

• Theoretical investigations on a novel CL-20/LLM-105 cocrystal explosive by
molecular dynamics method

Abstract: Abstract The hexanitrohexaazaisowurtzitane/2,6-diamino-3,5-dinitropyrazine-1-oxide (CL-20/LLM-105) cocrystal models with different component ratios were established by the substitution method. The stability, sensitivity, energetic performance, and mechanical properties of CL-20, LLM-105, and CL-20/LLM-105 cocrystal models were predicted by the molecular dynamics method. The results show that the CL-20/LLM-105 cocrystal model with component ratio of 2:1 has the highest value of binding energy and is the most stable model. The cocrystal model has shorter trigger bond length than pure CL-20, but higher value of trigger bond energy and cohesive energy density, which implies that the sensitivity of cocrystal explosive is decreased. The cocrystal explosive has lower energy density than CL-20, but the cocrystal explosive with molar ratio of 10:1~2:1 still has high energy density and can be regarded as novel high energy density compound (HEDC). The tensile modulus, shear modulus, and bulk modulus of cocrystal models are decreased, Cauchy pressure is increased, meaning that the mechanical properties is improved. In a word, the CL-20/LLM-105 cocrystal explosive with component ratio of 2:1 has the best stability, lowest mechanical sensitivity, most desirable mechanical properties, and high energy density, it is very promising to become a novel HEDC.
PubDate: 2022-04-07

• Ciprofloxacin/Topoisomerase-II complex as a promising dual
UV–Vis/fluorescent probe: accomplishments and opportunities for the
cancer diagnosis

Abstract: Abstract In this work, a dual UV–Vis/fluorescent probe to be used in cancer diagnosis is proposed by theoretical investigations of the interaction of ciprofloxacin (CPX) molecule with human Topoisomerase-II β enzyme, and its respective excited state properties. Molecular docking simulations suggest that CPX has similar inhibitory effects for human and bacteria Topoisomerase-II, and for human enzyme, CPX interacts preferentially in the same site of chemotherapeutic etoposide (EVP). In TD-DFT parametrization for CPX, it was found that Global Hybrid functionals containing around 25% of exact exchange contribution, such as mPW1PW91, M06 and PBE0, are most suitable for computing excitation energies for CPX. Also, explicit solvent model calculations allow results closer to the real. For excited state properties, theoretical calculations show that there are changes in absorption energy of CPX, and the distance between Tyrosine 821 residue of human enzyme and CPX can also enable a Fluorescence resonance energy transfer (FRET) between the two molecules. Therefore, it is suggested in this work that both the variation in the absorption energy of the CPX (UV–Vis spectra) and the variation in the excitation energy of Tyr (821) (Fluorescence spectra) can be used in a dual-sensor to monitor the overexpression of hTOPO-II, constituting a promising tool in cancer diagnosis.
PubDate: 2022-04-07

• Quantum study on the optoelectronic properties and chemical reactivity of
phenoxazine-based organic photosensitizer for solar cell purposes

Abstract: Abstract Meeting the requirements and developments of modern society will be unachievable without a sustainable source of energy. However, dye sensitized solar cell (DSSC) has been found worthy to produce reliable energy source. Recently, researchers have inputted great effort toward the modulation of organic dyes to achieve highly efficient dye sensitizers for solar cell purposes. Herein, D-π-A architectural design was employed to generate ten phenoxazine-based dye engineered with five different thiophene π-linkers and two acceptor units. Density functional theory (DFT) and time-dependent DFT were used to optimize the molecules in order to cognize their intramolecular charge transport, optoelectronic properties, light-harvesting efficiency (LHE) and open-circuit voltage (Voc). DFT conceptual was engaged to elucidate the chemical reactivity parameters of the photosensitizers. Among the π-linkers employed, 2,6-diethenylbisthieno[3,2-b:2′,3′-d]thiophene (D3) remarkably improved the intramolecular charge transfer, thus generated an exceptional HOMO/LUMO energy gap (Eg), strong bathochromic shift, suitable LHE and notable Voc. The qualities of the dyes were further enhanced by replacing 2-cyano-2-pyran-4-ylidene-acetic acid with cyanoacrylic acid acceptor moiety. Comparison of these systems with other reported molecules reveals that majority of the simulated poses improved properties that are recommendable for solar cells applications.
PubDate: 2022-04-06

• Lewis acid-catalyzed Diels–Alder cycloaddition of 2,5-dimethylfuran and
ethylene: a density functional theory investigation

Abstract: Abstract Density functional theory calculations with the M06-2X exchange–correlation functional have been performed to explore the Diels–Alder reaction between 2,5-DMF and ethylene as well as to compare the uncatalyzed reaction to the one catalyzed by the AlCl3 Lewis acid. The uncatalyzed reaction corresponds to a normal electron-demand (NED) mechanism where ethylene is an electron acceptor and 2,5-DMF plays the role of electron donor. This reaction presents a low polar character, its kinetics is little impacted by the solvent dielectric constant, and the formation of the two new σ bonds occurs through a one-step synchronous process. When the LA interacts with ethylene, forming a π-complex, it enhances its acceptor character, further favoring the NED mechanism, which is accompanied by a reduction of the free energy of the transition state. On the other hand, when AlCl3 is complexed by 2,5-DMF, the inverse electron-demand (IED) mechanism is favored, with ethylene playing the role of the donor. Within both NED and IED mechanism, the LA-catalyzed reaction takes place via a one-step asynchronous process. In addition, it is highly polar, so that the activation barrier decreases with the solvent polarity. Moreover, the calculations have evidenced that the LA forms stable complexes with any of the reactants so that the gain on the activation barrier amounts to 9–12 kcal mol−1 for the NED mechanism and to 3–9 kcal mol−1 for the IED one and that the formation of Al2Cl6 dimers impacts the different equilibria. Finally, the decrease of the activation barrier goes in pair with the reduction of the HOMO–LUMO gap, with the greatest decrease recorded when the LA interacts with ethylene according to the NED mechanism.
PubDate: 2022-04-04

• Au12C68: a hollow noble metal carbide

Abstract: Abstract A hollow cage-like Au12C68 structure with Th symmetry was investigated based on first-principles density functional theory calculation. This structure is seamed together of 12 AuC13 subunits, and there are three pentagons and one hexagon in each AuC13 subunits. The 12 gold atoms form an icosahedral configuration with Th symmetry. Subsequently, the stability of Au12C68 cage has been verified by vibrational frequency analysis and ab initio molecular dynamics simulations. Electronic structure analysis shows that clearly sp–d hybridizations between Au atoms and C atoms are of great importance for the stability of Au12C68 cage. Moreover, the Au12C68 molecule is magnetic with spin magnetic moment of 3.97 µB. This hollow Au12C68 cage with magnetic properties may lead to important applications in single-molecule devices.
PubDate: 2022-04-01

• Computation of photovoltaic and stability properties of hybrid
organic–inorganic perovskites via convolutional neural networks

Abstract: Abstract Hybrid organic–inorganic perovskites (HOIPs) have gained considerable interest due to their potential applications as photovoltaic materials. Nevertheless, several issues have to be solved on this matter, such as the proper tuning of band gaps and those concerning stability, before these systems can realise their full potential. Here, we used deep learning techniques, more specifically crystal graph neural networks (Xie & Grossman, Phys. Rev. Let., 2018, 120), abbreviated as CGNN, to explore the chemical space of HOIPs and to address the above mentioned difficulties. We trained this CGNN with a data set comprised of 1346 density functional theory calculations and used it to compute band gaps, refractive indexes, atomisation energies, volumes of unit cells and volumetric densities of 3840 HOIPs. Our screening method permits a rapid selection of perovskites with suitable optoelectronic properties and only 7 have an adequate band gap to be used in photovoltaic technologies. The composition, ABX $$_3$$ , of such perovskites is mainly of small molecular cations such as A = $$\mathrm {[NH_4]^+}$$ , $$\mathrm {[NH_2NH_3]^+}$$ together with $$\mathrm {[OHNH_3]^+}$$ , B = $$\mathrm {In^2+}$$ , $$\mathrm {Zr^2+}$$ along with $$\mathrm {Sn^2+}$$ , and X = I $$^-$$ . The consideration of further systems indicates that the occurrence of phosphorus and sulphur in the molecular cation diminishes strongly the band gap of the perovskite. We also considered the stability of the systems with optimal band gaps with respect to their degradation in simple organic and inorganic salts. Overall, our investigation shows how deep learning techniques can be exploited to achieve a rapid screening of potential photovoltaic materials in terms of their electronic properties and stability.
PubDate: 2022-03-28

• First-principles DFT insights into the mechanisms of CO2 reduction to CO
on Fe (100)-Ni bimetals

Abstract: Abstract Iron and nickel are known active sites in the enzyme carbon monoxide dehydrogenases which catalyzes CO2 to CO reversibly. The presence of nickel impurities in the earth abundant iron surface could provide a more efficient catalyst for CO2 degradation into CO, which is a feedstock for hydrocarbon fuel production. In the present study, we have employed spin-polarized dispersion-corrected density functional theory calculations within the generalized gradient approximation to elucidate the active sites on Fe (100)-Ni bimetals. We sort to ascertain the mechanism of CO2 dissociation to carbon monoxide on Ni deposited and alloyed surfaces at 0.25, 0.50 and 1 monolayer (ML) impurity concentrations. CO2 and (CO + O) bind exothermically i.e., − 0.87 eV and − 1.51 eV respectively to the bare Fe (100) surface with a decomposition barrier of 0.53 eV. The presence of nickel generally lowers the amount of charge transferred to CO2 moiety. Generally, the binding strengths of CO2 were reduced on the modified surfaces and the extent of its activation was lowered. The barriers for CO2 dissociation increased mainly upon introduction of Ni impurities which is undesired. However, the 0.5 ML deposited (FeNi0.5(A)) surface is promising for CO2 decomposition, providing a lower energy barrier (of 0.32 eV) than the pristine Fe (100) surface. This active 1-dimensional defective FeNi0.5(A) surface provides a stepped surface and Ni–Ni bridge binding site for CO2 on Fe (100). Ni–Ni bridge site on Fe (100) is more effective for both CO2 binding or sequestration and dissociation compared to the stepped surface providing the Fe–Ni bridge binding site.
PubDate: 2022-03-22

• Analyzing cases of significant nondynamic correlation with DFT using the
atomic populations of effectively localized electrons

Abstract: Abstract Quantum multireference effects are associated with degeneracies and near-degeneracies of the ground state and are critical to a variety of systems. Most approximate functionals of density functional theory (DFT) fail to properly describe such effects. A number of diagnostics have been proposed to estimate in advance the reliability of a given single-reference solution in this respect. Some of these diagnostics, however, lack size-consistency while remaining computationally expensive. In this work, we propose the DFT method of atomic populations of effectively localized electrons (APELE) as a novel diagnostic in this vein. It is compared with existing diagnostics of nondynamic correlation on select exemplary systems. The APELE method is on average in good agreement with the popular T1 index, while being size-consistent and less costly. It becomes particularly informative in cases involving bond stretching or bond breaking. The APELE method is applied next to organic diradicals like the bis-acridine dimer and the p-quinodimethane molecule which possess unusually high nonlinear optical response, and to the reaction of ethylene addition to Ni dithiolene. Our results for this reaction are consistent with the T1 diagnostics and in addition, shed some light on the degree of d-electron localization at the Ni center.
PubDate: 2022-03-15

• Coupling density functional based tight binding with class 1 force fields
in a hybrid QM/MM scheme

Abstract: Abstract Quantum Mechanics/Molecular Mechanics (QM/MM) hybrid methods have become very popular schemes to incorporate environmental effects in the calculation of molecular properties, when it is mandatory to have both a quantum description of electrons to compute these properties and an atomistic description of the environment. However, even Density Functional Theory/MM schemes may become timecosting when a large part of the system should be treated at the QM level or when plenty of single point energy calculations are intended to be done. We report a new implementation, within the deMonNano code, of a hybrid QM/MM scheme combining the density functional based tight binding with class 1 force fields. Two types of additive couplings can be chosen, namely the mechanical coupling, consisting of a Lennard-Jones potential and the electrostatic coupling, in which the MM part of the system is also polarizing the region described at the QM level. As first test-case application, the harmonic infrared spectra of simple molecules in the gas phase and in water clusters are computed and compared to those obtained at the DFT/MM level. Binding energies are also compared. Similar trends are obtained with the two levels of calculations and the main differences are discussed.
PubDate: 2022-03-12

• Theoretical study of the substituent effect on the O–H insertion
reaction of copper carbenoids

Abstract: Abstract In this paper, we will study the reactivity along with substituent changes in the OH insertion reaction in copper carbenoids. To this end, we have used M06-2X functional with cc-pVDZ for light atoms and LanL2DZ for copper. We have studied the IRC insertion profiles and analysed reactivity indexes such as electrophilicity (ω) and pKa calculations. We have found that with R1 substitutions phenyl group, R2 substitutions amide group lower the reaction barrier considerably. Concerning the substrate reactions, the most favoured substituent is NO2 in para position.
PubDate: 2022-03-11

• Aggregation or dispersion of Si atoms in Al–Si alloys' from the
view point of energetics

Abstract: Abstract Al–Si binary system forms eutectic alloys with about 12% Si and their mechanical and physical properties are strongly related to the distribution of eutectic silicon in the microstructure. This paper studies the structures of Al32-nSin (n = 2, 4, 6, 8) crystals by using global evolutionary algorithm combined with density functional theories. The lowest energy structures are determined and the bonding strengths of the Al–Al, Al–Si and Si–Si bonds are evaluated. The binding energies of the alloy crystals increase considerably with the silicon content and the dispersion of silicon atoms is favorable for the stability. At given composition, the dispersion of Si atoms forms two Al–Si bonds at the expense of one Al–Al and one Si–Si bonds and the energy gain is 0.022 eV. The mechanical properties are investigated and the calculated moduli show that the shear modulus and Young’s modulus are related obviously to the silicon composition and distributions while the bulk moduli are quite close for all of the alloy structures. The moduli values are largest for Al28Si4 (its silicon content is close to the eutectic) and its Young’s modulus is 31% larger than the pure aluminum.
PubDate: 2022-03-10

• The ethanol–metal interaction in bimetallic clusters of Pt and Rh

Abstract: Abstract The comprehension of the reaction mechanism for ethanol steam reforming over metal particles requires the knowledge of the forces governing the ethanol–metal interaction. In this work, we used a combination of wave function analysis techniques (NCI, QTAIM, CMOEDA and NBO) to unveil the chemical origin of the ethanol–metal interaction in bimetallic clusters of Pt and Rh of varied proportions (Pt $$_5$$ Rh, Pt $$_4$$ Rh $$_2$$ , Pt $$_3$$ Rh $$_3$$ , Pt $$_2$$ Rh $$_4$$ and PtRh $$_5$$ ). These clusters are highly polarized with the Pt atoms bearing the negative charge. This polarization guides the interaction with ethanol which complexes by orienting an oxygen lone pair over the most positive cluster site. In this way, a O–Rh contact is observed in most of the bimetallic clusters, although in the pure clusters the O–Pt interaction is stronger. QTAIM shows that the O–Metal interaction in the bimetallic clusters weakens as more Rh atoms are present, but the final complexation energy is a balance between several factors. NBO analysis describes the complexation as a compromise between donation of charge from oxygen to the cluster, back donation from the cluster to oxygen and, in some cases, the formation of a hydrogen bond involving the O–H bond and a partially negative Pt atom in the cluster.
PubDate: 2022-03-08
DOI: 10.1007/s00214-022-02877-7

• Dihydrogen attachment and dissociation reactions in Fe(H)2(H2)(PEtPh2)3: a
DFT potential-energy scan

Abstract: Abstract A special class of hydrogen-binding metal complexes are complexes able to bind hydrogen molecules at one or more of their ligand positions. One of such complexes, Fe(H)2(H2)(PEtPh2)3, was characterized experimentally and theoretically in previous works. Its specific properties were related to the asymmetry of the non-hydrogen ligands. Following this reasoning, attachment and dissociation of hydrogen molecule to and from the 5-coordinated and 6-coordinated complex were investigated theoretically. Relaxed and partially constrained potential-energy scans were performed and transition-states for these processes were investigated. Non-hydrogen ligand asymmetry seems to reflect on the different barrier energies for approach to and dissociation from the two dihydrogen ligand positions. Steric and environment effects are estimated comparing behavior for partially constrained and gas-phase models. On the basis of these findings, theoretically predicted pathways for single-step dihydrogen binding and dissociation processes are established, and means for experimental verification are proposed.
PubDate: 2022-02-27
DOI: 10.1007/s00214-022-02870-0

• The reliability of the small-core lanthanide effective core potentials

Abstract: Abstract The reliability of the small-core lanthanide effective core potentials (ECP) is tested using MF and MF $$_3$$ , for M=Eu, Gd, Tb, and Yb and the atomic excitation energies for Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. In some case, the ECP and all-electron (AE) results are in good agreement, while in others there are significant differences. The differences are much larger when the segmented basis set is used in conjunction with the ECP than when the atomic natural orbital (ANO) basis set is used. The study of the atoms suggests that problems for lanthanide-containing molecules are associated with poor atomic excitation energies in the ECP treatment and even using the ANO basis set does not completely solve the problem. We note that the problem appears to be more severe for density functional approaches than for traditional correlation methods. We suggest that additional studies and new effective core potentials may be required for the lanthanide atoms.
PubDate: 2022-02-26
DOI: 10.1007/s00214-022-02867-9

• A DFT study of the molecular and electronic structures of
cis-dioxidomolybdenum (VI) complex of 8-hydroxyquinoline and
4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one with water

Abstract: Abstract Density functional theory approaches are employed to elucidate the structural features and electronic properties of cis-dioxidomolybdenum(VI) complexes with water, 8-hydroxyquinoline and 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one. Geometrical parameters are optimized using B3PW91, B3LYP functionals in conjunction with def2-TZVP, LanL2DZ and 6-311 + G basis sets. Computed results show that the complex energetically prefers a pseudo-pentagonal bipyramidal shape in the ground state. The nature of intramolecular interactions between Mo(VI) and ligands is evaluated by analyzing the natural bond orbital and quantum theory of atoms in molecules. The Mo–OH2 interaction is rather weak with an average distance of 2.445 Å and a very low Mayer bond order of 0.235. The vibrational signatures and vertical electronic transitions of some excitations are examined and compared to available experimental data. The most favorable sites for electrophilic, nucleophilic attack or protonation were also identified using the noncovalent interaction method.
PubDate: 2022-02-16
DOI: 10.1007/s00214-022-02868-8

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