Theoretical study of spectroscopic constants and molecular properties of rare‐gas diatomic cations

Ab initio and density functional methods are applied to study the spectroscopic constants and molecular properties of the diatomic cations He, Ne, Ar, HeNe⁺, and HeAr⁺. Among these cations, HeAr⁺ is found to be weakly bound and its spectroscopic constants are calculated using the Lennard‐Jones potential. The other molecules that are strongly bound obey Morse potential, and their spectroscopic constants are calculated accordingly. The calculated spectroscopic constants agree very well with the theoretical and experimental values wherever available. Most of the spectroscopic constants and molecular properties are reported for the first time. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A combinatorial study of inverse Heusler alloys by first‐principles computational methods

In continuation of our recent combinatorial work on 810 X₂YZ full Heusler alloys, a computational study of the same class of materials but with the inverse (XY)XZ crystal structure has been performed on the basis of first‐principles (GGA) total‐energy calculations using pseudopotentials and plane waves. The predicted enthalpies of formation evidence 27 phases to be thermochemically stable against the elements and the regular X₂YZ type. A chemical‐bonding study yields an inherent tendency for structural distortion in a majority of these alloys, and we predict the existence of the new tetragonal phase Fe₂CuGa (P4₂/ncm; a = 5.072 Å, c = 7.634 Å; c/a ≈ 1.51) with a saturation moment of μ = 4.69 μ_B per formula unit. Thirteen more likewise new, isotypical phases are predicted to show essentially the same behavior. Six phases turn out to be the most stable in the inverse tetragonal arrangement. The course of the magnetic properties as a function of the valence‐electron concentration is analyzed using a Slater‐Pauling approach. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

A first‐principles study on the existence and structures of the lighter alkaline‐earth pernitrides

The lighter alkaline‐earth pernitrides BeN₂, MgN and CaN₂ have been structurally predicted by a series of density‐functional (GGA/PBE/PAW) electronic‐structure calculations. Despite their crystal chemistry clearly pointing towards the formulation M²⁺N₂^2? with an N? N distance of 1.26 Å, all phases turn out as metallic compounds which are exothermic with respect to the elements. The M²⁺ coordination numbers are a simple function of the cationic radius. The bulk moduli are about three times smaller than those of the noble‐metal pernitrides, a consequence of the smaller anionic charge in the former phases. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Chemical surface passivation of 3C‐SiC nanocrystals: A first‐principle study

The effect of the chemical surface passivation, with hydrogen atoms, on the energy band gap of porous cubic silicon carbide (PSiC) was investigated. The pores are modeled by means of the supercell technique, in which columns of Si and/or C atoms are removed along the [001] direction. Within this supercell model, morphology effects can be analyzed in detail. The electronic band structure is performed using the density functional theory based on the generalized gradient approximation. Two types of pores are studied: C‐rich and Si‐rich pores surface. The enlargement of energy band gap is greater in the C‐rich than Si‐rich pores surface. This supercell model emphasizes the interconnection between 3C‐SiC nanocrystals, delocalizing the electronic states. However, the results show a clear quantum confinement signature, which is contrasted with that of nanowire systems. The calculation shows a significant response to changes in surface passivation with hydrogen. The chemical tuning of the band gap opens the possibility plenty applications in nanotechnology. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2455–2461, 2010     

Interaction potential models for bulk Zns,Zns nanoparticle,and Zns nanoparticle‐PMMA from first‐principles

An ab initio derived transferable polarizable force‐field has been developed for Zinc sulphide (ZnS) nanoparticle (NP) and ZnS NP‐PMMA nanocomposite. The structure and elastic constants of bulk ZnS using the new force‐field are within a few percent of experimental observables. The new force‐field show remarkable ability to reproduce structures and nucleation energies of nanoclusters (Zn₁S₁‐Zn₁₂S₁₂) as validated with that of the density functional theory calculations. A qualitative agreement of the radial distribution functions of Zn? O, in a ZnS nanocluster‐PMMA system, obtained using molecular mechanics molecular dynamics (MD) and ab initio MD (AIMD) simulations indicates that the ZnS–PMMA interaction through Zn? O bonding is explained satisfactorily by our force‐field. © 2015 Wiley Periodicals, Inc.     

Electronic structure and coordination chemistry of phenanthridine ligand in first‐row transition metal complexes: A DFT study

The geometric parameters, electronic structures, and haptotropic migration of a series of hypothetical compounds of general formula CpM(C₁₃H₉N) and (CO)₃M(C₁₃H₉N) (M = fist row transition metal, Cp = C₅H₅, and C₁₃H₉N = phenanthridine ligand) are investigated by means of the density functional theory. The phenanthridine ligand can bind to the metal through η¹ to η⁶ coordination mode, in agreement with the electron count and the nature of the metal, showing its capability to adapt itself to the electronic demand of the metal as well as to the polycyclic aromatic hydrocarbons. In the investigated species, the most favored closed‐shell count is 18‐electron except for the Ti and V models which are deficient open‐shell 16‐electron configuration. This study has shown the difference in coordination ability of this heteropolycyclic ligand: the coordination of the central C₅N ring is less favored than the terminal C₆ rings, in agreement with the π‐electron density localization. Most of the investigated complexes are expected to exhibit a rich fluxional behavior. This flexibility favors the possibility for the existence of several isomers as well as their interconversion through haptotropic shifts. © 2012 Wiley Periodicals, Inc.     

Effective band gap reduction of titanium oxide semiconductors by codoping from first‐principles calculations

Doping is an efficient approach to narrow the band gap of TiO₂ and enhance its photocatalytic activity. Here, we perform generalized gradient approximation (GGA)+U calculations to narrow the band gap of TiO₂ by codoping of X (F, N) with transition metals (TM = Fe, Co) to extend the absorption edge to longer visible‐light wavelengths. Our results show that all the codoped systems can narrow the band gap significantly, in particular, (F+Fe)‐codoped system could serve as remarkably better photocatalysts with both narrowing of the band gap and relatively smaller formation energies than those of (F+Co) and (N+TM)‐codoped systems. Our results provide useful guidance for codoped TiO₂ efficient for photocatalytic activity. © 2013 Wiley Periodicals, Inc.     

DFT assessment of the spectroscopic constants and absorption spectra of neutral and charged diatomic species of group 11 and 14 elements

The spectroscopic constants and absorption spectra of neutral and charged diatomic molecules of group 11 and 14 elements formulated as [M₂]^+/0/? (M = Cu, Ag, Au), and [E₂]^+/0/? (E = C, Si, Ge, Sn, Pb) have been calculated at the PBE0/Def2‐QZVPP level of theory. The electronic and bonding properties of the diatomics have been analyzed by natural bond orbital analysis approach and topology analysis by the atoms in molecules method. Particular emphasis was given on the absorption spectra of the diatomic species, which were simulated by time‐dependent density functional theory calculations employing the hybrid Coulomb‐attenuating CAM‐B3LYP density functional. The simulated absorption spectra of the [M₂]^+/0/? (M = Cu, Ag, Au) and [E₂]^+/0/? (E = C, Si, Ge, Sn, Pb) species are in close resemblance with the experimentally observed spectra whenever available. The neutral M₂ and E₂ diatomics strongly absorb in the ultraviolet region, given rise to UVC, UVA and in a few cases UVB absorptions. In a few cases, weak absorbion bands also occur in the visible region. The absorption bands have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made. © 2014 Wiley Periodicals, Inc.     

Electronic structure and spectroscopic properties of 6‐aminophenanthridine and its derivatives: Insights from density functional theory

6‐Aminophenanthridine (6AP) and its derivatives show important biological activities as antiprion compounds and inhibitors of the protein folding activity of the ribosome. Both of these activities depend on the RNA binding property of these compounds, which has been recently characterized by fluorescence spectroscopy. Hence, fundamental insights into the photophysical properties of 6AP compounds are highly important to understand their biological activities. In this work, we have calculated electronic structures and optical properties of 6AP and its three derivatives 6AP8CF₃, 6AP8Cl, and 6APi by density functional theory (DFT) and time‐dependent density functional theory (TDDFT). Our calculated spectra show a good agreement with the experimental absorption and fluorescence spectra, and thus, provide deep insights into the optical properties of the compounds. Furthermore, comparing the results obtained with four different hybrid functionals, we demonstrate that the accuracy of the functionals varies in the order B3LYP > PBE0 > M062X > M06HF. © 2015 Wiley Periodicals, Inc.     

Crystal structure and spectroscopic characterization of a cobalt(II) tetraazamacrocycle: completing a series of first‐row transition‐metal complexes

The tetraazamacrocyclic ligand 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane (TMC) has been used to bind a variety of first‐row transition metals but to date the crystal structure of the cobalt(II) complex has been missing from this series. The missing cobalt complex chlorido(1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane‐κ⁴N )cobalt(II) chloride dihydrate, [CoCl(C₁₄H₃₂N₄)]Cl·2H₂O or [Co^IICl(TMC)]Cl·2H₂O, crystallizes as a purple crystal. This species adopts a distorted square‐pyramidal geometry in which the TMC ligand assumes the trans‐I configuration and the chloride ion binds in the syn‐methyl pocket of the ligand. The Co^II ion adopts an S = spin state, as measured by the Evans NMR method, and UV–visible spectroscopic studies indicate that the title hydrated salt is stable in solution. Density functional theory (DFT) studies reveal that the geometric parameters of [Co^IICl(TMC)]Cl·2H₂O are sensitive to the cobalt spin state and correctly predict a change in spin state upon a minor perturbation to the ligand environment.     

Spectroscopic constants and molecular properties of rare‐gas diatomic molecule in Lennard‐Jones potential: Ab initio and density functional study

Ab initio and density functional theory (DFT) are applied to study the spectroscopic constants, molecular properties, and nature of force between two rare gas atoms of the weakly bound diatomic molecules He₂, Ne₂, Ar₂, HeNe, and HeAr in the Lennard‐Jones potential. A simple method is developed to calculate the spectroscopic constants of these molecules. The calculated spectroscopic constants and molecular properties agree very well with the experimental and theoretical results wherever available. Most of the spectroscopic constants and molecular properties are reported for the first time. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electronic structure,chemical bonding,and oxidation numbers of first‐row transition metals in [MePIm2] complexes and their cations

The qualitative structures of the upper one‐electron energy levels of imidazole‐coordinated first‐row transition metal porphyrin [MePIm₂] complexes established in the present study have shown that the second oxidation number of the first‐row transition metals in the neutral complexes do not change in their cations and double cations. It was found that occupied orbitals of the density functional theory method obtained with B3LYP functional are not correctly ordered. Therefore, they cannot be used in investigations of the orbital structure of the upper molecular orbitals. A qualitative analysis of density functional theory method wave functions in terms of Mulliken and natural charges of atoms, together with an analysis of electrostatic potentials of the neutral [MePIm₂] complex, its single and double cations, demonstrates that the highest occupied orbitals of these complexes are mainly formed by atomic orbitals of the porphyrin ring atoms. Therefore, transition metal atoms are not active in chemical reactions with these complexes unless the 3d electrons of transition metal atoms are excited, for example by light. A mechanism of an electron transfer reaction that occurs between a heme cytochrome and Fe‐oxide mineral surface is discussed in the light of the obtained results. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Analytical potential energy functions and theoretical spectroscopic constants for MX/MX− (MGe,Sn, Pb; XO,S, Se,Te, Po) and LuA (AH,F) systems: Density functional theory calculations

The molecular spectroscopic constants for the chalcogenide complexes MX (M?Ge, Sn, Pb; X?O, S, Se, Te, Po) and their corresponding MX^? anions are presented with the LSDA/SDD, B1LYP/SDD, and B3LYP/SDD methods. Although many methods were attempted, only the most promising results are reported. We show that the best results are obtained by LSDA/SDD calculations, and thus this method is emphasized as an illustrative example of our methodology. The potential energy curves and physical property characterizations for X¹ ∑⁺ state of LuH and LuF are presented with a variety of density functional theory (DFT) methods. Comparisons with wave function‐based treatments (HF, MP2, CCSD, QCISD) are made in addition to experimental correlations. We show that the best results are obtained by the B3LYP/SDD method for LuH, and the MPW1PW91/SDD method for LuF. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Structural,spectroscopic and first‐principles studies of new aminocoumarin derivatives

The new aminocoumarin derivatives 3‐[1‐(3‐hydroxyanilino)ethylidene]‐3H‐chromene‐2,4‐dione, ( 1 ), 3‐[1‐(4‐hydroxyanilino)ethylidene]‐3H‐chromene‐2,4‐dione, ( 2 ), and 3‐[1‐(2‐hydroxyanilino)ethylidene]‐3H‐chromene‐2,4‐dione, ( 3 ), all C₁₇H₁₃NO₄, were synthesized by reacting an equimolar amount of 3‐acetyl‐4‐hydroxycoumarin and the corresponding aminophenol in absolute ethanol. Structural and spectroscopic analysis of these phases revealed that derivatives ( 1 ) and ( 2 ) are isomers of previously reported ( 3 ) [Brahmia et al. (2013). Acta Cryst. E 69 , o1296]. The crystal structures of meta derivative ( 1 ) and para derivative ( 2 ) were ab initio determined from powder X‐ray diffraction data using the direct‐space approach. Both ( 1 ) and ( 2 ) adopt the orthorhombic space group P2₁2₁2₁. These isomers show hydrogen bonds and rich π–π stacking, together with π…H interactions, which are built by conjugated systems of coumarin and phenol rings. In the crystalline lattice, the packing of ( 1 ) and ( 3 ) are mainly stabilized through O—H…O hydrogen bonding between neighbouring coumarin molecules, while hydrogen bonds between coumarin and water molecules build the stable crystal structure of derivative ( 2 ). A big similarity in the skeletons of the IR spectra of these isomers was noticed. Derivative ( 2 ) exhibits two weak bands which were not present in the spectra of the other two derivatives, at 2370 and 2948 cm^?1, which can be assigned to the O—H vibrations of the solvent (H₂O) trapped in the structure of ( 2 ). These aminocoumarin derivatives display absorption maxima in the visible region, attributed to π–π delocalization involving the whole electronic system of the compounds with a considerable charge‐transfer character originating from the aminophenyl ring and pointing towards the coumarin system which is characterized by a high electron‐accepting character. Additionally, the isolated molecular ground‐state geometries were optimized at the PBE0/TZP level and the electronic properties, molecular electrostatic potential and Hirshfeld charges were determined.     

Nonfitting protein–ligand interaction scoring function based on first‐principles theoretical chemistry methods: Development and application on kinase inhibitors

Targeted therapy is currently a hot topic in the fields of cancer research and drug design. An important requirement for this approach is the development of potent and selective inhibitors for the identified target protein. However, current ways to estimate inhibitor efficacy rely on empirical protein–ligand interaction scoring functions which, suffering from their heavy parameterizations, often lead to a low accuracy. In this work, we develop a nonfitting scoring function, which consists of three terms: (1) gas‐phase protein‐ligand binding enthalpy obtained by the eXtended ONIOM hybrid method based on an integration of density functional theory (DFT) methods (XYG3 and ωB97X‐D) and the semiempirical PM6 method, (2) solvation free energy based on DFT‐SMD solvation model, and (3) entropy effect estimated by using DFT frequency analysis. The new scoring function is tested on a cyclin‐dependent kinase 2 (CDK2) inhibitor database including 76 CDK2 protein inhibitors and a p21‐activated kinase 1 (PAK1) inhibitor database including 20 organometallic PAK1 protein inhibitors. From the results, good correlations are found between the calculated scores and the experimental inhibitor efficacies with the square of correlation coefficient R² of 0.76–0.88. This suggests a good predictive power of this scoring function. To the best of our knowledge, this is the first high level theory‐based nonfitting scoring function with such a good level of performance. This scoring function is recommended to be used in the final screening of lead structure derivatives. © 2013 Wiley Periodicals, Inc.     

Crystal structures and thermodynamic investigations of NaSc(BH4)4 from first‐principles calculations

The double cation borohydride NaSc(BH₄)₄ has a total H₂ content of 12.67 wt.% and has been suggested as a potential candidate for hydrogen storage applications. This study reports first‐principles calculations of the structure and reaction thermodynamics of NaSc(BH₄)₄. The calculations indicate that NaSc(BH₄)₄ is decomposed into a mixture of ScB₂, NaBH₄, and Na₂(B₁₀H₁₀) with H₂ release of 9.3 wt.% at 118 K at a partial pressure of H₂ of 100 bar. Reactant compositions that can destabilize NaSc(BH₄)₄ were evaluated. This effort identified four destabilization reactions that are predicted to have reaction thermodynamics for hydrogen release within the temperature range of 78–109 K. Even though the reactions conclusively produce undesired compounds, such as refractory materials or kinetically stable B₁₂H₁₂‐containing species, the thermodynamic study suggests a direction for improving the thermodynamics of double cation borohydride‐based systems being actively considered for hydrogen storage applications. © 2012 Wiley Periodicals, Inc.     

A general,recursive, and open‐ended response code

We present a new implementation of a recent open‐ended response theory formulation for time‐ and perturbation‐dependent basis sets (Thorvaldsen et al., J. Chem. Phys. 2008, 129, 214108) at the Hartree–Fock and density functional levels of theory. A novel feature of the new implementation is the use of recursive programming techniques, making it possible to write highly compact code for the analytic calculation of any response property at any valid choice of rule for the order of perturbation at which to include perturbed density matrices. The formalism is expressed in terms of the density matrix in the atomic orbital basis, allowing the recursive scheme presented here to be used in linear‐scaling formulations of response theory as well as with two‐ and four‐component relativistic wave functions. To demonstrate the new code, we present calculations of the third geometrical derivatives of the frequency‐dependent second hyperpolarizability for HSOH at the Hartree–Fock level of theory, a seventh‐order energy derivative involving basis sets that are both time and perturbation dependent. © 2014 Wiley Periodicals, Inc.     

Analytical nuclear excited‐state gradients for the Tamm–Dancoff approximation using uncoupled frozen‐density embedding

We report the derivation and implementation of analytical nuclear gradients for excited states using time‐dependent density functional theory using the Tamm–Dancoff approximation combined with uncoupled frozen‐density embedding using density fitting. Explicit equations are presented and discussed. The implementation is able to treat singlet as well as triplet states and functionals using the local density approximation, the generalized gradient approximation, combinations with Hartree–Fock exchange (hybrids), and range‐separated functionals such as CAM‐B3LYP. The new method is benchmarked against supermolecule calculations in two case studies: The solvatochromic shift of the (vertical) fluorescence energy of 4‐aminophthalimide on solvation, and the first local excitation of the benzonitrile dimer. Whereas for the 4‐aminophthalimide–water complex deviations of about 0.2 eV are obtained to supermolecular calculations, for the benzonitrile dimer the maximum error for adiabatic excitation energies is below 0.01 eV due to a weak coupling of the subsystems. © 2017 Wiley Periodicals, Inc.