In this study, the improved Tietz potential was used to describe the internal vibration of a diatomic molecule. With the help of the expression for bound state energy levels, a more generalized equation for the upper bound vibrational quantum number and canonical partition function were obtained for the diatomic system. The obtained partition function was used to derive analytical equation for the prediction of constant pressure (isobaric) molar heat capacity of diatomic molecules. The analytical model was used to predict the constant pressure molar heat capacity data of the ground state CO, BBr, HBr, HI, P2, KBr, Br2, PBr, SiO and Cl2 molecules. The upper bound vibrational quantum number obtained for the molecules are 85, 100, 21, 21, 115, 301, 89, 157, 110 and 67. The computed average absolute deviation are 2.3462%, 1.1342%, 2.3350%, 1.9078%, 0.7268%, 2.4041%, 1.7849%, 1.8989%, 2.5209% and 2.1523%. The present results are in good agreement with available literature data on gaseous molecules.

In this account we report an implementation of the quantum trajectory-guided adaptive Gaussian (QTAG) method in a modular open-source Libra package for quantum dynamics calculations. The QTAG method is based on a representation of wavefunctions in terms of a quantum trajectory-guided adaptable Gaussians basis and is generalized for time-propagation on multiple coupled surfaces to be applicable to model nonadiabatic dynamics. The potential matrix elements are evaluated within either the local harmonic or bra-ket-average (linear) approximations to the potential energy surfaces, the latter being a more practical option. Performance of the QTAG method is demonstrated and discussed for the Holstein and Tully models, which are the standard benchmarks for method development in the area of nonadiabatic dynamics.

Singlet and triplet spin state energies for three-dimensionalHooke atoms, i .e. electrons in a quadratic confinement, with even number of electrons (2, 4, 6, 8, 10) is discussed using Full-CI and CASSCF type wavefunctions with a variety of basis sets and considering perturbative corrections up to second order. The effect of the screening of the electron-electron interaction is also discussed by using a Yukawa-type potential with different values of the Yukawa screening parameter (λee =0.2, 0.4, 0.6, 0.8, 1.0). Our results show that the singlet state is the ground state for 2 and 8 electron Hooke atoms, whereas the triplet is the ground spin state for 4, 6 and 10 electron systems. This suggests the following Auf bau structure 1s < 1p < 1d with singlet ground spin states for systems in which the generation of the triplet implies an inter-shell one electron promotion, and triplet ground states in cases when there is a partial filling of electrons of a given shell. It is also observed that the screening of electronelectron interactions has a sizable quantitative effect on the relative energies of both spin states, specially in the case of 2 and 8 electron systems, favouring the singlet state over the triplet. However, the screening of the electron-electron interaction does not provoke a change in the nature of the ground spin state of these systems. By analyzing the different components of the energy, we have gained a deeper understanding of the effects of the kinetic, confinement and electron-electron interaction components of the energy.

Exploring the space generated by the self-assembly of known metal oxides computationally and the ability to predict new architectures is a challenging task. Narrowing it down to a family of all-inorganic porous materials, composed of ring-shaped tungsten oxide building blocks connected with transition metal linkers forming zero to three dimensional frameworks. Structurally like zeolites (213 recognized structures), but an order of magnitude smaller, the POMzite library has only 14 members. Applying the concept of ‘materials by design’ applied to molecular metal oxide chemistry synthesis, and their assembly into frameworks. Structures with new topologies, but aiming for pure inorganic systems, will be targeted from the beginning.

To cope with the energy crisis and global warming issues, researcher are rendering their efforts and paying their attentions to analyze and fabricate hydrogen storage devices. In this regard, we report a comprehensive study on the structural, vibrational, and optoelectronic properties of Lithium Borohydride (LiBH4), a hydrogen storage material. For this purpose, calculations of structural properties have been made using the local, non-local and hybrid functionals within the framework of density functional theory (DFT). The lattice constants for the orthorhombic phase are determined by applying LDA, PBE and HSE06 density functionals and their results are compared with available experimental and theoretical studies. In order to determine IR and Raman active modes of vibrations, vibrational spectroscopy has been utilized through Density Functional Perturbation Theory (DFPT) approach. Li, B and H atoms are noticed to be contributing in the modes of vibrations between different ranges of frequencies, i.e., 0 to 400 cm-1, 1100 to 1300 cm-1 and 2250 -2400 cm-1. The respective values of band gaps are found to be 6.35 eV, 6.81 eV and 7.58 eV for LDA, PBE and HSE06 functionals, respectively, leading to indicate insulating nature of LiBH4 which makes it a promising candidate for applications in optoelectronic devices. The mechanical analysis reveals that LiBH4 is a brittle material. The optical properties such as dielectric constant, refractive index, reflectivity, absorptivity, conductivity and loss function are also calculated with the aid of well-recognized relation of Kramer-Kronig. The plasma frequency is noted at the highest peak (13.7 eV) of the energy loss function.

Here we show that substituting the ten protons in the dianion of a bispentalene derivative (C18H102-) by six Si2+ dications produces a minimum energy structure with two planar tetracoordinate carbons (ptC). In Si6C18, the ptCs are embedded in the terminal C5 pentagonal rings and participate in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Our exploration of the potential energy surface identifies a triphenylene derivative as the putative global minimum. But robustness to Born-Oppenheimer molecular dynamics (BOMD) simulations at 900 and 1500 K supports bispentalene derivative kinetic stability. Chemical bonding analysis reveals ten delocalized π-bonds, which, according to Hückel’s 4n+2 π-electron rule, would classify it as an aromatic system. Magnetically induced current density analysis reveals the presence of intense local paratropic currents and a weakly global diatropic current, the latter agreeing with the possible global aromatic character of this specie.

The initial configuration of Yttrium oxide clusters (Y2O3)n(n=1-15) was creatively constructed by combining artificial bee colony algorithm with density functional theory. The structures of large and medium-sized yttrium oxide clusters with molecular number greater than 10 were established for the first time, and many new structures that are different from existing research have been obtained. The average binding energy, second-order difference energy, HOMO-LUMO gap, density of states and other properties of the clusters were analyzed. The thermodynamic properties and behavior of nano yttrium oxide clusters at different temperatures and sizes were discussed. Studies have shown that for small-sized clusters, the atomic stacking structure is cage-like, while for medium-sized and large-sized clusters, the composite trapezoidal structure and ellipsoid-like structure are more stable. The nanoclusters tend to be stable as a whole, and the relative stability of the cluster structure is higher when n = 2,4,7,9. The effect of yttrium oxygen atomic orbital on bonding is analyzed. The heat capacity (Cp), enthalpy change (H) and entropy (S) of (Y2O3)n (n=1-15) clusters increase with the increase of temperature (T), and the vibration free energy (Gv) decreases with the increase of T. The stability of the clusters changes in the temperature range of 300K-500K.

Density functional theory, or DFT, has become ubiquitous for chemical applications in research and in education. The exact functional at the foundation of DFT is unfortunately unknown, and issues arise when choosing an approximation for a specific application. With this tutorial review, we tackle the selection problem and many related ones, such as the choices of a basis set and of an integration grid, that are often overlooked by occasional practitioners and by more experienced users as well. We offer a practical approach in the form of a commented notebook containing 12 experiments that can be run on a simple computer in just a few hours. We propose this review as a primary source for those who are willing to include DFT in their everyday research or teaching activities in a way that reflects the research advances of the field in the last couple of decades

Group IV organometallic complexes are promising systems for C-H bond activation. We are interested in the C-H bond activation of the CH2 positions of the adamantyl group, since these positions are particularly hard to activate and to functionalize. As a potential platform for activation of that important alkyl group, we consider the alkyl bonded to the cyclopentadienyl in a substituted bis-cyclopentadienyl group IV metal diphenyl complex. The mechanism proposed in the classic paper reporting such activation using Zr(IV) (Erker and Mühlenbernd, 1987) involves an η2-benzyne complex intermediate. This current work reports a computational analysis of the problem through Density Functional Theory (DFT). We found that the two-step mechanism proposed for activation of C(Me)2-Ph or tert-Bu groups using Zr(IV) is indeed confirmed by DFT and that it can be extended to Ti and Hf. We further found that the system can be successfully extended to the adamantyl group. The first step involves formation of the benzyne complex, which can also be described as a metallacyclopropene. In the second step, the cyclopentadienyl-bound alkyl is activated in the coordination sphere of the metal via proton transfer to the bound benzyne, which, if the metallacyclopropene description is chosen, resembles a σ-bond metathesis. The C-H bond activation of adamantyl through this approach is thermodynamically and kinetically feasible. Selective α-CH bond activation should be achievable with Ti (under thermodynamic control), and selective γ-CH bond activation with Zr (under kinetic or thermodynamic control).

The urgent desire for Halon substitution propels the exploration of potential alternatives, because of the severe damage of Halons to the stratospheric ozone layer. In this paper, the thermal decomposition mechanism, as well as fire-extinguishing mechanism and performance of Trifluoroiodomethane (CF3I) were studied by density functional theory (DFT) calculation and experimental measurements, to analyze the practicability of this proposed Halon substitute. The thermal decomposition products of CF3I can react with active OH· and H· radicals to achieve the purpose of rapidly fire-extinguishing. Besides, through DFT calculation and reaction kinetics analysis, the fire-extinguishing radicals CF3· and I· are more easily generated during the interaction between CF3I and flame, which indicates the chemical- extinguishing mechanism and pronounced fire-extinguishing performance of CF3I. To explore its actual fire-extinguishing effect, the fire-extinguishing concentration (FEC) of CF3I was measured in cup burner. The FEC value of this proposed Halon substitute is 3.42vol% for extinguishment of methane-air flame, which is smaller than those of three HFCs and HFO-1336mzz(Z) and is comparable to that of Halon 1301. These findings suggest the promising applicability of CF3I in practical Halon replacement and the necessity of further evaluation.

Diels-Alder cycloaddition reaction is helpful to produce covalent derivatives of fullerene with desirable electronic and physical properties. In the present venture, we have computationally investigated the reactivity of neutral C60 and its Li+ encapsulated derivative towards Multi-Diels-Alder (MDA) reaction with 1,3-butadiene, employing density functional theory (DFT). The computational reports available to date illustrate the functionalization of fullerene surfaces of neutral and encapsulated C60 (Ca and Sm) with two butadiene molecules. In this article, we aim to investigate whether more than two butadiene molecules can be attached to the fullerene surface or not. To do so, we have shown that the MDA reaction initiates with the formation of an encounter complex between the mono-functionalized fullerene product and the second butadiene molecule. In this context, two different approaches, namely ‘Direct’ and ‘Alternative’ have been considered based on the attachment of the second butadiene, i.e., whether it is attached to the opposite or adjacent position of the first functionalization, which eventually produces the same final product. We have explored the MDA reactions by considering a total of four diene molecules that can be embedded successfully on the fullerene surface, with each reaction step having a high degree of exothermicity, thus making the overall reaction thermodynamically facile. In harmony with the mono- and bis-cycloaddition reactions, for MDA reaction also, the positive impact of Li+ encapsulation for enhancing the reactivity of fullerene surface towards butadiene attachment is evident from our study. On-the-fly calculations also suggest the bond preference for [6, 6] connectivity than its [6, 5] counterpart, to be the suitable dienophile, just like the mono- and bis-functionalization reported earlier. Overall, the present study will foresee an extensive idea about the detailed mechanism of the MDA reaction on neutral C60 and Li+@C60 that could encourage the scientists to perform the aforementioned reaction for other fullerene derivatives in the long run.

I would like to submit an erratum for the article with the title ‘Development of Kinetic Energy Density Functional Using Response Function Defined on the Energy Coordinate’ (Int. J. Quantum Chem. 2022;e26969, https://doi.org/10.1002/qua.26969). The corresponding author of the article is Hideaki Takahashi. The author found an error in producing the graph with the legend ‘OF-DFT’ in Fig. 8 in the article. The error in the graph is attributed to the fact that the atomic response function was spuriously multiplied by 2. We refer the editor to the main text of the erratum in more details. The graph was revised using the amended source code. Fortunately, it was found that the corrected graph was changed favorably as compared to the original one, showing better agreement with the reference calculation.

In this study, the photovoltaic properties of the organic dyes based on triphenylamine having a D--A structure including TC201, TC202, TC203, TC601, H-P, F-P, FF-P, T-F, and P1B were investigated theoretically. In this model, triphenylamine was used as an electron donor, cyanoacrylic acid, and benzoic acid as the electron acceptors, and anthracene phenyl, anthracene vinyl phenyl, anthracene ethynyl phenyl, ethynyl anthracene phenyl, styryl phenyl, styryl-2-fluorophenyl, styryl-2,6-difluorophenyl, styryl furan, and styryl as the π-conjugated systems. The results show that a change in the -conjugated system and electron acceptor affect the properties of the dye-sensitized solar cell (DSSC). Also, TC601 dye having the ethynyl anthracene phenyl -conjugated system shows the highest charge transfer distance (DCT) and the least overlap of the electron-hole distribution (S) in comparison with other dyes. Moreover, the presence of a triple bond in the vicinity of triphenylamine increases the resonance effect of the -electrons that facilitates the process of charge transfer in this dye. Spectroscopic analysis shows that H-P and F-P dyes have the higher molecular absorption coefficients and TC202, TC203, F-P, and T-F dyes show a red shift in comparison with other dyes. Moreover, the voltage-current curve of the studied dyes shows that the highest values of the open circuit voltage and short circuit current density are related to P1B and TC601 dyes, respectively. Finally, TC601 and P1B are proposed as the best candidates to be used in the DSSCs due to their maximum incident photon to current conversion efficiency.

The realization of fractional quantum chemistry is presented. Adopting the integro-differential operators of the calculus of arbitrary-order, we develop a general framework for the description of quantum nonlocal effects in the complex electronic environments. After a brief overview of the historical and fundamental aspects of the calculus of arbitrary-order, various classes of fractional Schr\"odinger equations are discussed and pertinent controversies and open problems around their applications to model systems are detailed. We provide a unified approach toward fractional generalization of the quantum chemical models such as Hartree-Fock and Kohn-Sham density functional theory and develop fractional variants of the fundamental molecular integrals and correlation energy . Furthermore, we offer various strategies for modeling static- and dynamic-order quantum nonlocal effects through constant- and variable-order fractional operators, respectively. Possible directions for future developments of fractional quantum chemistry are also outlined..

In this paper, an elegant and easy to implement numerical method using matrix mechanics approach is proposed, to solve the time independent Schrodinger equation (TISE) for Morse potential. It is specifically applied to non-homogeneous diatomic molecule HCl to obtain its rotating-vibrator spectrum. While matrix diagonalization technique is utilised for solving TISE, model parameters for Morse potential are optimized using variational Monte-Carlo (VMC) approach by minimizing χ 2 − value. Thus, validation with experimental vibrational frequencies is completely numerical based with no recourse to analytical solutions. The ro-vibrational spectra of HCl molecule obtained using the optimized parameters through VMC have resulted in least χ 2 − value as compared to those determined using best parameters from multiple regression analysis of analytical expressions. Numerical algorithm for solving the Hamiltonian matrix has been implemented utilizing Free Open Source Software (FOSS) Scilab and simulation results are matching well with those obtained using analytical solutions from Nikiforov-Uvarov (NU) method and asymptotic iteration method (AIM).

Models of surface enhancement of molecular electronic response properties are challenging for two reasons: (1) molecule-surface interactions require the simultaneous solution of the molecular and the surface dynamic response (a daunting task); (2) when solving for the electronic structure of the combined molecule+surface system, it is not trivial to single out the particular physical effects responsible for enhancement. To attack this problem, in this work we apply a formally exact decomposition of the system’s response function into subsystem contributions by employing subsystem DFT which grants access to dynamic polarizabilities and optical spectra. In order to access information about the interactions between the subsystems, we extend a previously developed subsystem-based adiabatic connection fluctuation-dissipation theorem of DFT to separate the additive from the nonadditive correlation energy and identify the nonadditive correlation as the van der Waals interactions. As an example, we choose benzene adsorbed on monolayer MoS2. We isolate the contributions to the benzene’s dynamic response arising from the interaction with the surface and for the first time, we evaluate the enhancements to the effective C6 coefficients as a function of benzene-MoS2 distance and adsorption site. We also quantify the spectral broadening of the benzene’s electronic excited states due to their interaction with the surface. We find that the broadening has a similar decay law with the molecule-surface distance as the leading van der Waals interactions (i.e., R-6) and that the surface enhancement of dispersion interactions between benzene molecules is less than 5\%, but still large enough (0.5 kcal/mol) to likely play a role in the prediction of interface morphologies.

Magnesium-based hydrogen storage material (MgH2) has attracted much attention due to its high hydrogen storage density (7.6 wt%). However, the high hydrogen dissociation enthalpy and slow hydrogen dissociation rate in bulk Mg hinder its wide application in the efficient hydrogen storage. In the present work, we study the hydrogen adsorption and desorption reactions of MgmHn (m = 1-6) nanoclusters using density functional theory (DFT). From the global search for the configurations of MgmHn nanoclusters, we found not only stable saturated MgmHn (n = 2m) nanoclusters, but four hydrogen-enriched MgmHn (n:m>2:1) nanoclusters, Mg3H7, Mg4H9, Mg5H11, Mg6H13, with the hydrogen storage density higher than 8.3 wt%. The electronic-structure calculations indicate that the stability of the hydrogen-enriched cluster gets relatively higher for larger nanocluster. The ab initio dynamics simulations shows that all hydrogen-enriched clusters have very fast hydrogen dissociation rates, which is promising for the hydrogen dissociation at ambient temperature and pressure. This work provides insights into the hydrogen storage mechanism of nano-magnesium materials.

Theoretical elucidation of the turn-off mechanism of the luminescence of a chemosensor based on a metal-organic framework (MOF) [Zn2(OBA)4(BYP)2] (BYP: 4,4’-bipyridine; H2OBA: 4,4’-oxybis(benzoic acid)), selective to nitrobenzene via quantum chemical computations is presented. The electronic structure and optical properties of Zn-MOF were investigated through the combination of density functional theory (DFT) and time-dependent-DFT methods. Our results indicate that the fluorescence emission is governed by a linker (BPY) to linker (OBA) charge transfer (LLCT) involving orbitals π-type. Next, interaction with the analyte was analyzed, where very interesting results were obtained, i.e. the LUMO is now composed by orbitals from nitrobenzene, which changes the emissive state of the Zn-MOF. This fact suggests that the LLCT process is blocked, inducing then the fluorescence quenching. Otherwise, the Morokuma-Ziegler energy decomposition and NOCV (Natural Orbitals for Chemical Valence) on the Zn-MOF-nitrobenzene interactions were studied in detail, which illustrate the possible channels of charge transfer between Zn-MOF and nitrobenzene. Finally, we believe that this proposed methodology can be applied to different chemosensor-analyte systems to evidence the molecular and electronic factors that govern the sensing mechanisms.