The first-order relativistic corrections to the non-relativistic energies of hydrogen-like atom embedded in plasma screening environments are calculated in the framework of direct perturbation theory by using the generalized pseudospectral method. The standard Debye-Hückel potential, exponential cosine screened Coulomb potential, and Hulthén potential are employed to model different screening conditions and their effects on the eigenenergies of hydrogen-like atoms are investigated. The relativistic corrections which include the relativistic mass correction, Darwin term, and the spin-orbit coupling term for both the ground and excited states are reported as functions of screening parameters. Comparison with previous theoretical predictions shows that both the relativistic mass correction and spin-orbit coupling obtained in this work are in good agreement with previous estimations, while significant discrepancy and even opposite trend is found for the Darwin term. The overall relativistic-corrected system energies predicted in this work, however, are in good agreement with the fully relativistic calculations available in the literature. We finally present the scaling law of the first-order relativistic corrections and discuss the validity of the direct perturbation theory with respect to both the nuclear charge and the screening parameter.
In silico search for planar hexacoordinate silicon center has been initiated by global minimum screening with density functional theory and energy refinement using coupled cluster theory. The search resulted in a local minimum of SiAl3Mg3H2+ structure which contains a planar hexacoordinate silicon center (phSi). The phSi structure is 5.8 kcal/mol higher in energy than the global minimum. However, kinetic studies reveal that the local minimum structure has enough stability to be detected experimentally. Born-Oppenheimer molecular dynamics (BOMD) simulations reveal that the phSi structure can be maintained up to 400 K. The formation of multiple bonds between the central silicon atom and framework aluminium atom is the key stabilizing factor for the planar structure.
It is well noticed that hydrogen promotes catalyst activity in Cr/PNP-catalyzed ethylene tetramerization, but the mechanism of this boost is unclear. A density functional theory (DFT) study devoted to exploring this effect was conducted, and conformation changes were carefully taken into consideration to build a clear reaction pathway. Three components in the catalytic cycle was examined in detail: the production of 1-hexene from the metallacycloheptane, the production of 1-octene from metallacyclononane, and the formation of active center on the catalyst. The result indicates that the formation of active center on the catalyst becomes more favorable upon imposition of hydrogen, where hydrogen function as a second ligand. This easing effect could be the key factor leading to the outperformed catalyst activity.
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).
Finding effective anchoring materials for the immobilization of soluble lithium polysulfides to suppress the shuttling effect has become the key to large-scale application of lithium-sulfur (Li–S) batteries. In this work, the potentials of group-VA two-dimensional (2D) materials including arsenene, antimonene and bismuthene (As, Sb and Bi monolayers) as Li-S battery cathode anchoring materials were systematically investigated by density functional theory (DFT) calculations. The adsorption energies of sulphur (S8) and various lithium polysulfides (Li2Sn, n = 8, 6, 4, 2, 1), as well as the diffusion energy barriers for long-chain Li2S4 and Li2S6 on these three monolayers were studied in detail. The calculated moderate adsorption energies of these monolayers to all polysulfides imply that they can effectively inhibit the shuttling effect. The favorable diffusion barriers for Li2S4 and Li2S6 ensure the efficient diffusion of polysulfides on monolayer surface. In addition, these 2D materials can keep a balance between the binding strength and the structural integrity of polysulfides. The presented merits demonstrate that As, Sb and Bi monolayers can be the promising cathode anchoring materials to improve the performance of Li-S batteries.
Aiming at improving the visible-light photocatalytic activities of TiO2(101) surface (TiOS) we make an in-dept study on the TiOS doped with 4d transition metal (TM) atoms. It is shown that the 4d TM dopings can not only produce new impurity energy bands in the bandgap but also result in the semiconductor-metal phase transition. Consequently, the visible-light absorption is strongly strengthened due to the dopings of Y, Zr, Nb, Mo, and Ag, while it is only weakly improved for Tc, Ru, Rh, Pd, and Cd dopings. The improvement in visible-light absorption can be attributed to the intraband or interband transition of electrons. Moreover, the photocatalytic activities are explored, and we find Y and Ag dopings can effectively enhance the photocatalytic activity of TiOS. Thus the mechanism of improving photocatalytic activity of TiOS has been clearly addressed, which is beneficial to further experimental and theoretical researches on TiO2 photocatalysts.
This work concerns the typical conformational behaviors for di-substituted cyclohexanes that inherently depend on spatial orientations of side chains in flexible cyclic ring. The 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane in both cis- and trans-configurations were focused here to unravel their conformational inversion-topomerization mechanisms. Full geometry optimizations were performed at B3LYP/6-311++G(d,p) level of theory to explicitly identify all distinguishable molecular structures, and thus explore potential energy surfaces (PES) of the complete interconversion routes for two stereoisomers of 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane. Additional quantum calculations were carried out by separately applying MP2/6-311++G(d,p), G4, and CCSD(T)/6-311++G(d,p) methods to further refine all PES’ stationary points. With respect to quantum results, the conformational analysis was conducted to gain insight into the determination, thermodynamic stabilities, and relative energies of distinct molecular geometric structures. On base of highly biased conformational equilibria, the temperature-dependent populations of stable local minima for four studied dimethylcyclohexanes were obtained by utilizing Boltzmann distribution within 300-2500 K. Moreover, two unique interconversion processes for them, including inversion and topomerization, were fully investigated, and their potential energy surfaces were illustrated with the rigorous descriptions in two or three-dimensional schemes for clarify.
4-(2-Methoxyethyl) phenol (MEP) is an significant methoxypheolic compound, which has been shown to play an important role in the formation of secondary organic aerosols(SOA). The present work focuses on the gas-phase oxidation mechanism and kinetics of MEP and OH radical by the density functional theory (DFT). Energetically favourable reaction channels and feasible products were identified. The initial reactions of MEP with OH radical have two different channels: OH addition and H abstraction. Subsequent reaction schemes of main intermediates in the presence of O2 and NOx are investigated using quantum chemical methods at M06-2X/6-311++G(3df,2p)//M06-2X/6-311+G(d,p) level. Ketene, Phenyldiketones and nitrophenol compounds are demonstrated to be possible oxidation products. The total rate constant(1.69×10-11 cm3 molecule-1 s-1) and individual rate constant are calculated using the traditional transition state (TST) theory at 298K and 1atm. The lifetime of MEP is estimated to be 16.4 hours, which provides a comprehensive explanation for atmospheric oxidation pathway of MEP and shows MEP would be removed by OH radical in the atmosphere.
The present work is intended to bring to the forefront a relatively less explored area of N-Heterocyclic Carbene (NHC) catalyzed alkyne hydro- thiolation and selenation reactions. The present work can be regarded as the first ever computational investigation on the catalytic activity of the NHC catalyzed hydro- thiolation and selenation reactions by exploring the reaction mechanism. Reaction mechanism involves chalcogenol activation followed by alkyne insertion and the second step is found to be the rate determining step. A comparison with the reported uncatalyzed gas phase reaction showed that a simple imidazol-2-ylidene catalyst can lower the free energy barrier by 19.62 and 14.63 kcal/mol respectively for acetylene hydro- thiolation and selenation reaction. All the employed NHCs are proved to be better catalyst for both hydrothiolation and hydroselenation. Effects of factors such as changing the heterocycle, increasing the conjugation, ring expansion and electronic/steric substitution were also investigated. Effect of solvent polarity on the reaction energetics and selectivity has also been analyzed employing THF, DMSO and MeOH as the solvents.
In the context of non-relativistic quantum mechanics, we use information theory to study Shannon’s entropy of a non-Hermitian system and understand how the information is modified with the cyclotron frequency. Subsequently, we turn our attention to the construction of an ensemble of these spinless particles in the presence of a uniform magnetic field. Then, we study the thermodynamic properties of the model. Finally, we show how information and thermodynamic properties are modified with the action of the magnetic field. KEYWORDS: Non-relativistic Quantum Mechanics; Quantum Information; Shannon Entropy.
The geometries of monocharged and neutral octafluoro-spirobi[triphosphazene] in singlet, doublet and/or triplet ground spin states were optimized. Their electronic structures are investigated in terms of Quantum Theory of Atoms-in-Molecules and compared with neutral hexafluorocyclotriphosphazene. The change of the total molecular charge implies mainly the change of the properties of the nitrogen atoms which are bonded to the central spiro-phosphorus atom. The charged systems in singlet spin states have stable structures of D2d symmetry only unlike the remaining ones of C2 symmetry within two geometry types. The existence of the less symmetric structures can be fully explained as a consequence of the (pseudo-) Jahn-Teller effect.
We report the electronic, elastic, mechanical, optical and magnetic properties of Rh2MnX (X=Ti, Hf, Sc, Zr, Zn) Heusler alloys performed within density functional theory (DFT). The generalized gradient approximation (GGA) was used for calculations in the context of the Perdew-Burke-Ernzerhof (PBE) exchange-correlation energy treatment. The computed elastic constants and elastic moduli show that all investigated alloys are mechanically stable and ductile. It has been found that the magnitudes of the theoretical Vickers hardness values of these alloys are in the range of Ti> Sc> Zr> Hf> Zn. Also, a typical metallic behavior is obtained for all alloys after agreement of mechanical, electronic and optical data. On the other side, all alloys show strong ferromagnetic ordering following the magnetic moment ( µB ) rank of Ti > Zr > Hf > Sc > Zn. Our calculated µB data also agree well with the former theoretical results of Rh2MnX (X=Ti, Hf, Sc, Zr, Zn) Heusler alloys.
Two-dimensional (2D) materials have exhibited exceptional properties which meet the demands of future applications. These materials appeared after discovery of graphene in 2004 offered such device grade characteristics at nanoscale which did not appear on bulk scale. The research turned to search alternate 2D materials when drawbacks of graphene became surfaced. Despite significant successes and unprecedented efforts which consequent upon several beyond-graphene 2D materials, the complete potentials of such materials are still unexplored which may restrict their usage in devices. This work was carried out with motivation to investigate the thermal stability of several 2D-mono-layered materials including graphene, Borophene, Aluminene, Germanene, BN, SiC and MoS2 based on classical Molecular Dynamics Simulations. Prior to the implementation of the conditions for thermal calculations, the structures were optimized using Geometry-Optimization method. It appeared that all the structural parameters which includes lattice-constant, bond-length and dihedral angles were precisely determined. On the contrary, it was found that several materials beyond graphene can resist up-to certain temperature ranges, depicting the material dependent thermal stability. The radial distribution function (RDF) was calculated which pointed towards thermal broadening, bond breakage and bond formation for the slabs. The RDF-peaks were found to characterize the probability of finding any particle in the nearest neighbors which extend the phenomenon of thermal stability. Thermal stability was compared by plotting the temperature and energy curves from which, the phase transition temperature and heat capacity was determined for the slabs including graphene as benchmark. The phase transition temperatures are found as 4510 K, 2273 K, 933 K, 1670 K, 3246 K, 4050 K, and 1460 K for graphene, Borophene, Aluminene, Germanene, BN, SiC and MoS2 respectively. Besides the analysis of temperature-energy variations, the thermal broadening is also determined and discussed to examine the thermal-stability for usage of the materials in high temperature applications.
By doping two potassium atoms among three C20F20 cages, peanut-shaped single molecular solvated dielectron (C20F20)3&K2 was theoretically presented. The triplet structures with two excess electrons individually inside left and middle cages (isomers I or II) are thermodynamically more stable than both open-shell (OS) and close-shell (CS) singlet ones with lone pair of excess electrons inside middle cage. Applying an oriented external electric field (OEEF) of -20 × 10-4 au (-0.1018 V/Å) or a larger one can result in both left-to-right transfers of the two excess electrons, and then releasing the OEEF can form new kind of inter-cage electron-transfer isomers (III or IV). Each triplet I ~ IV with three redox sits may be new members of mixed-valent compounds, namely, Robin-Day Class II. For electrified I of (C20F20)3&K2 , the following spin states are ground state: 1) triplet state in field ranges of -120 × 10-4 < Fx < -30 × 10-4 au and 30 × 10-4 < F-4 < 111 × 10-4 au; 2) CS singlet state in range of Fx ≥ 111 × 10-4 and ≤ -120 × 10-4 au; 3) OS singlet state in ranges of -30 × 10-4 ≤ Fx ≤ -5 × 10-4 au and 5 × 10-4 ≤ Fx ≤ 30 × 10-4 au.
A benchmark of anisotropic polarizabilities has been carried out for 14 (hetero)-aromatic molecules using the methods: RPA, RPA(D), HRPA, HRPA(D), SOPPA, SOPPA(CC2), SOPPA(CCSD), CC2, CCSD and CC3. While this benchmark, to a large extend, shows similar tendencies as found for isotropic polarizabilities, it also reveals some differences between isotropic and anisotropic polarizabilities. CCSD is found to be the method performing closest to CC3 as it also was for isotropic polarizabilities. For static anisotropic polarizabilities SOPPA(CCSD) performs incredibly close to CCSD, however, the less demanding HRPA(D) follows shortly after in precision. For dynamic anisotropic polarizabilities SOPPA(CCSD) is again the method least deviating from CC3, beside CCSD, but its standard deviation is worse than for RPA, which gives results only slightly more deviating from the CC3 results than SOPPA(CCSD). While the HRPA model is seen to perform incomparably worse than any of the other methods, the simpler RPA is on the other hand thus performing notably well. The finding of this good performance of the relatively simpler and cheaper methods, RPA and HRPA(D), permits calculation of much larger systems without sacrificing the quality of the calculation.
Adenosine triphosphate (ATP) hydrolysis is a well-known biological reaction which plays an important role in many biological processes. In this study, we have modelled the non-enzymatic hydrolysis of ATP in the gas-phase and the aqueous-phase by performing ab initio molecular dynamics simulations combined with an enhanced sampling technique. In the gas-phase, we studied hydrolysis of fully protonated ATP molecule and in the aqueous-phase, we studied hydrolysis of ATP coordinated with: a) two H+ ions (H-ATP), b) Mg2+ (Mg-ATP) and c) Ca2+ (Ca-ATP). We show that gas-phase ATP hydrolysis follows a two-step dissociative mechanism via a highly stable metaphosphate intermediate. The Adenine group of the ATP molecule plays a crucial role of a general base; temporarily accepting protons and, thus helping in the elimination-addition process. In the aqueous-phase hydrolysis of ATP, we find that the cage of solvent molecules increases the stability of the terminal phospho-anhydride bond through a well-known cage-effect. Further, we find that the aqueous-phase hydrolysis happens with the help of nearby water molecules, which assumes the role of a base assisting in proton diffusion through Grotthuss mechanism. We obtained much lower free-energy barriers for the aqueous-phase hydrolysis of ATP coordinated with divalent ions (Mg2+ and Ca2+) compared to hydrolysis of ATP coordinated with only H+ ions, suggesting a clear catalytic effect of the divalent ions. We find a single-step dissociative-type mechanism for Mg-ATP, while we find a SN-2-type concerted hydrolysis pathway for Ca-ATP.
The first-principles methods based on the density functional theory were employed to study the structural stability, segregation and work function of Mg doped with fourteen metal elements existing in human body. The calculated results show that there is a simple correlation between solid solution and segregation. Doping Sn, Y, Li, Gd, Nd, Sc and Zn atoms have a negative formation energy as well as a positive segregation energy. This suggests that these elements which are not easier to be dissolved in Mg matrix tend to segregate on the Mg (0001) surface. An opposite trend was observed for Ba, Fe, Mn, W, Sr, Ca and Mo. On the other hand, the electronic work function of Mg (0001) surface was increased significantly for doping Mo, W, Fe, and Mn, and was reduced markedly for Ba, Ca and Sr. For Li, Sn, Sc, Gd, and Y, their doping on Mg surface generate a relatively small change in work function. In addition, the relationships of corrosion behavior to segregation and work function were discussed. This study may provide an avenue for seeking a more appropriate alloying element of Mg alloys with improved corrosion resistance in biomedical applications.
It is imperative to study the long term corrosion problems of nickel alloys in acidic medium due to breakdown of their passitive oxide. Focus of this work is to enhance the knowledge of adsorption of organic additives (OPD & PPD) onto the Ni-W alloy surface. Deducing the scenario of competitive adsorption of salen-type symmetrical Schiff bases (OPD, and PPD) as additive molecules on Ni-W alloy surface at molecular level was studied by Density Functional Theory (DFT), Monte Carlo simulation (MC), Molecular Dynamics simulation (MD) and Radial Distribution Function (RDF) analysis. Obtained intrinsic molecular parmaters from DFT shows a strong conformity to the corrosion effeciencies of experimental results. Higher polarization value of 650.707 a.u (PPD) explicates its electron donating ability onto the alloy surface. Higher binding energy (Ebinding=1132.241 kJ/mol) and spatial orientation of PPD molecule portrays the closest contacts between active atoms and alloy surface. Significant findings from DFT global descriptors, MC, MD and RDF analysis ratifies the corrosion effeciencies (PPD>OPD) of experimental outcomes, which correlates positively with the larger isomeric spacer. Overall, the present study, reports offers the corrosion inhibition resistance impact of OPD & PPD additives, revealing the fact of PPD as effective one and OPD as moderate ones for Ni-W alloys.