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.

Isomorphic titanium dichalcogenide TiX2 (X=S, Se, Te) compounds exhibit very diverse and anisotropic chemical and physical properties. The temperature dependent electrical resistivity of TiSe2 was found to exhibit anomalous behavior at low temperatures (< 200 K) which was connected to the emergence of a unique charge density wave (CDW), which was explained on the basis of 2a0×c0 superstructure formation, whereas bulk TiS2 and TiTe2 do not exhibit CDW instability. In order to understand their diverse nature, we have systematically investigated the electronic structure of titanium dichalcogenides by using the FPLAPW and PAW methods based on the density functional theory (DFT). The energy bands calculated by implementing the latest generalized gradient approximation (GGA) with PBE and TB-mBJ potentials confirm the semiconducting nature of TiS2 and metallic nature of TiSe2 and TiTe2, however the Wu-Cohen potentials show a semi-metallic nature for all three dichalcogenides. The diverse properties of TiX2 are governed by two bands, S/Se/Te p-band close to the Γ-point and Ti 3d-band around M (L)-points. The presence of electron and hole pockets at the Fermi energy level have been previously confirmed experimentally, although our calculated size and extent of overlap of these pockets was overestimated compared to experiments. Various physical parameters such as electrical conductivity, Seebeck coefficient etc. which depend sensitively on nature of states at the Fermi level also amply illustrate the diversity of the compounds. The electron localization function and Bader charge partitioning illustrate the increasing covalency with varying chalcogenide atom, which is consistent with the spectral features observed in the DOS. The lattice dispersion of the titanium dichalcogenides are calculated by using the PAW method with PBE potentials. The phonon band structure is correlated to the electronic band structure in order to explain the occurrence of CDW. In TiSe2, the presence of a phonon mode with imaginary frequency indicated lattice instability against distortion. The displacements of Ti-Se atoms of this phonon mode allows the mixing of states of the electron and hole pockets, which leads to lattice distortion i.e. a CDW structure which lowers the energy of the system. Although there is a weak imaginary mode, the mixing of states is absent in TiS2 due to absence of electron or hole pockets, whereas TiTe2 is structurally most stable.

The efficient computation of molecular integrals and their derivatives is a crucial step in molecular property evaluation in modern quantum chemistry. As an integral tensor decomposition technique, the density-fitting (DF) approach becomes a popular tool to reduce the memory and disk requirements for the electron repulsion integrals. In this study, an application programming interface (API) framework, denoted (MFW), for the computation of molecular integrals and their first derivatives, over contracted Gaussian functions, for the density-fitted methods is reported. The MFW is free software and it includes overlap, dipole, kinetic, potential, metric, and 3-index integrals, and their first derivatives. Furthermore, the MFW provides a smooth approach to build the Fock matrix and evaluate analytic gradients for the density-fitted methods. The MFW is a C++/Fortran hybrid code, which can take advantage of shared-memory parallel programming techniques. Our results demonstrate that the MFW is an efficient and user-friendly API for the computation of molecular integrals and their first derivatives.

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.

In this investigation we have used NG-QTAIM to fully quantity the response to the four IR-active modes of all the bonding in benzene in terms of bond-flexing, bond-torsion and bond-anharmonicity that includes the tendencies towards IR-responsivity and IR-non-responsivity. Bond-anharmonicity is found to be lacking for the C-C bonds comprising the lowest frequency mode (721.57 cm-1) measured as the absence of bond critical point (BCP) sliding. Additionally, bond-flexing was absent for this mode harmonic-like variation of the profile of the variation of the wrapping (torsion) of the {p,p’} path-packet, referred to as the Precession K, along the conventional QTAIM bond-path, the remaining three IR-active mode possessed step-like variations in the K profiles. The presence of non-nuclear attractors was detected for the IR-active mode with frequency 1573.93 cm-1 with C-C K profiles that most closely resemble those of the relaxed benzene. We quantified the C-H bonds in terms of bond-flexing and bond-anharmonicity and IR-responsivity and IR-non-responsivity.

Ligand field theory (LFT) calculations of energy levels were performed for the neutral actinide monooxides (AnO) and their singly and doubly ionized cations (AnO+ and AnO2+ by treating the molecular electronic states as Anm+ free-ion energy levels (where An ∈ Th through Lr and m=1, 2, 3, or 4) perturbed by the electric field of O2- or O-. LFT parameters obtained from fits to the energy levels of ThO, ThO+, UO, and UO+ were used to compute molecular energy levels for the lowest energy (maximum Sc, maximum Lc) 5f-core states of An4+, An3+, An2+, and An+ for the majority of the An4+O2-, An3+O-, An3+O2-, An2+O-, An2+O2- , and An+O- electronic configurations. Simple linear relationships enabled predictions of the dissociation energies for AnO, AnO+ and AnO2+ (where An ∈ Bk through Lr) and ionization energies for AnO and AnO+ (where An ∈ Bk through Lr), mainly based on recent accurate experimental data for the ionization energies of An atoms (where An ∈ Fm, Md, No, and Lr) and correlations with the energetics of the atoms and ions.