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The initial nucleation of gold clusters Aun (n = 1-5) on TiO2 rutile (110) reduced surface is studied using density functional theory and a full-potential augmented-plane-wave method implemented in the WIEN2k code. The first two gold atoms remained tied to the surface with a bond length similar to those belonging to other well-known related materials, while the other gold atoms do not spread over the surface; they preferred to form a new layer. The occurrence of relativistic effects produced a preferential triangle geometry for Au3 and a combination of triangular units for Au4 and Au5 . The Au-Au average distance increased from n = 2 to n = 5, indicating an expansion with a tendency to the bond distance found in the bulk. We are reporting an early 2D→3D transition of small folding, from Au3 →Au4 , followed by an Au4 →Au5 transition of evident 3D character.

For the first time, the structural and optoelectronic properties of a new complex formulated as CuBr2(C6H7N)2 (1) [trans-dibromidobis(3-methylpyridine-κN) copper(II)] were studied by density functional theory (DFT) calculations. They are performed using B3LYP through the Gaussian 09 program and also with full potential linearized augmented plane wave (FP-LAPW) methods within the Generalized Gradient Approximation (GGA) and Hartree-Fock (HF) theory by the Wien2k package. The neutral monomeric complex participates in a variety of non-covalent interactions, including hydrogen bonding and π stacking to create a 2D coordinate plane. The binding energy value of the non-covalent interactions responsible for the crystalline network formation of 1 were calculated using the method of dispersion corrected density functional theory (DFT-D). In this method, the independent smallest fragment (monomer) and subsequently the related network, including seven monomers bearing all non-covalent interactions were optimized. The results demonstrate that hydrogen bonds, especially non-conventional C–H···Br interactions, govern the network formation along the a and c axes. It can be mentioned because of these directed interactions, increasing of charge transfer along x and z directions results in increasement of the absorption and refractive index along y and z directions, and vice versa. The results of band structure show indirectly and directly the nature of the bandgap within GGA and HF, respectively. The bandgap value of CuBr2(C6H7N)2 is comparable to those of binary semiconductor compounds. DOSs spectra reveal that 3d Cu, 4p Br, and 2p C states play important roles in the optical transitions of the electrons. The calculated electronic absorption of the UV/Vis spectrum shows six major electron-transition bands derived from d → d (ligand field) n → n, n → π*, π → n, and σ → n MLCT and LMCT transitions. The calculated absorption spectrum of the titled complex through FP-LAPW within GGA method shows good consistency with the B3LYP/def2-TZVP/6-311+G(d,p) method. Our calculated birefringence results show that 1 has capability of nonlinear optical, which can be used in the nonlinear optoelectronic devices.

Crystallographic and electronic structures of binary compounds GaSe and InSe, known to exist in several polytype modifications, are discussed in comparison with those of chalcopyrite-type CuInSe2, CuGaSe2, and their solid solutions. The results are obtained within the density-functional theory (DFT), using two calculation codes, WIEN2k and VASP. The van der Waals interaction, important in stabilizing the structure of the layer compounds GaSe and InSe, was taken into account in the VASP calculation along the scheme of Grimme. For obtaining more realistic electronic band structures than is possible with the conventional generalized gradient approximation (GGA), the modified Becke–Johnson (mBJ) exchange–correlation (XC) potential was used, as implemented in the WIEN2k code. The results of two computer codes were compared in what concerns the optimization of the ground-state structures. The similarities in electronic structures of the systems studied are discussed under an angle of general trends proper to the compounds of Cu–(In,Ga)–Se composition.

Electron energy loss spectroscopy (EELS), in both the low loss and the core loss regions of the spectra, have been used to study local alloys composition, electronic transitions and bonding environment of different species in nanowires consisted of a GaN base-part and a superlattice upper part of InxGa1–xN nanodisks (NDs)/GaN barriers. Experimental valence (low loss) electron energy loss spectroscopy (VEELS) spectra were taken from the GaN base-part, the GaN barriers and the InxGa1–xN disks. Electron energy loss near edge structure (ELNES) spectra presenting the C K-edge, the N K-edge, the In M4,5-edge were obtained from the GaN base-part and spacer and the InxGa1–xN NDs. Variation of In concentration as well as different strain states change the intensity and result in the broadening and shifting of the edges in the spectra. The TELNES.2 program of the WIEN2k code (Blaha et al., Comp. Phys. Commun. 59, 399 (1990) [1]) was implemented in order to study the electronic properties of InxGa1–xN. The N K-edge that represents the energy loss of the electron transition from the 2p to the 1s state is unique for each structure. Details on the bonding environment of the structure were extracted from the simulations of the ELNES spectra. Moreover, the influence of the In content in the InxGa1–xN NDs on the N-K edge was interpreted. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

DFT (WIEN2k code, with modified Becke—Johnson potential) and the generalized gradient approximation-Perdew—Burke—Ernzerhof functional potential and Boltzmann theory calculations are performed to determine the electronic structures and electronic transport coefficients of AMN2 (A: Na, Cu; M: Ta, Nb) nitrides.

The adsorption and nucleation of gold clusters Aun (n = 1–5) on montmorillonite (MMT) is studied using the density functional theory. All the calculations were performed using the full-potential linearized augmented-plane-wave method as implemented in the WIEN2k code. We constructed a MMT supercell of formula Si16Al6Mg2O40(OH)8 containing four unit cells and the first moments of the nucleation process were studied by adding the gold atoms one by one on the MMT. The results show that the interaction energies between the gold clusters and the MMT are negative indicating that the Aun–MMT complexes are stable. In the Aun–MMT systems (n = 3–5), two gold atoms maintain the coordination with basal oxygens and the AuO distance was about 2.0–2.3 A. The AuAu average distance is 2.6 A in the supported gold clusters. The formation of the second layer of gold atoms occurs upon the arrival of the third gold atom. We are reporting that the transition of 2D 3D gold cluster structures is located from Au3 to Au4 on MMT. The total density of states of clusters Au, Au2, Au3, Au4, and Au5 on MMT allows us to affirm that (i) gold atoms are the main contributors to the states closest to the Fermi level and (ii) in Au4–MMT and Au5–MMT systems, the main contributors to the states closest to the Fermi level are the most external gold atoms, and therefore these atoms are probably the most susceptible to interact with adsorbates and the most active sites. Odd–even oscillations in the values of the energy gap and interaction energy were found: the odd-numbered supported clusters, Au3 and Au5, have larger energy gaps and more negative interaction energies. © 2012 Wiley Periodicals, Inc.

Doping ZnO with Eu results in the hybridization of the f atomic orbitals of the Eu with the bands of the host material. The strongest interaction turns out to be with the oxygen s-p band. This hybridization manifests itself as a Kondo-like resonance, namely, the appearance of a narrow resonant f band close to the Fermi level. Our aim in the present work is to calculate the electronic structure of ZnO:Eu in which the lanthanide ion replaces one of the Zn ions inducing a geometric relaxation on the system. We have used two reliable crystal electronic structure codes for our calculation. The program WIEN2k [Blaha, P., et al. WIEN2k, An Augmented Plane Wave + Local Orbitals Program for Calculating Crystal Properties, 2001] allows us to include the effects of the f the GGA + U model (generalized gradient approximation plus U) for the relaxed configuration. On the other hand, the program CRYSTAL06 [http://www.crystal.unito.it/] allows us to monitor the charge of the Eu ion using a judicious mix of the Hartree-Fock nonlocal exchange term with the density functional exchange-correlation potential. Results are presented for the density of states (both the total and the partial contribution from the f electrons), as well as maps of the spin density around the Eu ion, both clearly showing the presence of the resonant f bands. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

In order to investigate the electronic and magnetic properties of Co-ZnO alloys, we used a full potential linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT), as implement in the WIEN2K package. This work is carried out within the LSDA approximation as the exchange-correlation potential. We have modeled ZnO doped with 6.25, 12.5, and 18.75% of Co. It pointed out that the band gap decrease and the magnetic moments increase with the atomic fraction of Cobalt. The Zn x Co 1-x O is found to be a semiconductor, where the filled-states are located in the valence bands and the empty ones above the conduction band edge. The filled and empty d-states are also shown to shift downwards and upwards in the valence and the conduction bands, respectively, with increase in the U potential. The analysis of the partial density of states reveals that the reduction of the ZnO band gap is due principally to the strong p-d interaction of O and Co.

The complex density-functional theory (DFT) calculations of structural, electronic and optical properties for the three phases: wurtzite (B4), zincblende (B3) and rocksalt (B1) of ZnO compound have been reported using the full-potential linearized-augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We employed both the local-density approximation (LDA) and the generalized-gradient approximation (GGA), which is based on exchange–correlation energy optimization to calculate the total energy. Also, we have used the Engel–Vosko GGA formalism, which optimizes the corresponding potential for band-structure calculations. The 3d orbitals of the Zn atom were treated as the valence band. The calculated structural properties (equilibrium lattice constant, bulk modulus, etc.) of the wurtzite and rocksalt phases are in good agreement with experiment. The B4 structure of ZnO is found to transform to the B1 structure with a large volume collapse of about 17%. The phase transition pressure obtained by using LDA is about 9.93 in good agreement with the experimental data. B1-ZnO is shown to be an indirect bandgap semiconductor with a bandgap of 1.47 eV, which is significantly smaller than the experimental value (2.45 ± 0.15 eV). While B3 and B1 phases have direct bandgap semiconductors with bandgaps 1.46 and 1.57 eV, respectively. Also, we have presented the results of the effective masses. We present calculations of the frequency-dependent complex dielectric function e (ω) and it zero-frequency limit e1(0). The optical properties of B4 phase show considerable anisotropic between the two components. The reflectivity spectra has been calculated and compared with the available experimental data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Using the modified method of augmented plane waves and the code WIEN2k the calculations of the electron band structure, densities of electron states, and imaginary part of dielectric response function were carried out for different polarization of the vector of electrical field e xx and e zz for the semiconductor compounds ZnS, CuGaS 2 , and InPS4. The calculations were performed both for undisturbed crystals and for distorted crystals due to the applied pressure. The compounds studied have the similar crystallographic structures: ZnS - sphalerite, CuGaS 2 - chalcopyrite, and InPS4 - twice defective chalcopyrite. It is known, that in cubic ZnS there is no birefringence, whereas in CuGaS 2 and InPS4 there is one. But CuGaS 2 has so called isotropic point (where e xx = e zz ) in the visible optical range, and InPS4 has no such point. Our calculations of e xx and e zz have shown that in ZnS under the pressure the isotropic points arise, but in InPS4 they do not exist.

The electronic structure, electronic charge density, and band gaps of Ba2MYTe5 (M: Ga, In) single crystals are simulated using the full potential linearized augmented plane wave package WIEN2k.

Ab initio frozen-phonon calculations have been performed for k = 0 Ag Raman modes of superconducting GdBa2Cu3O7 and insulating PrBa2Cu3O7. We have used the generalized gradient approximation full-potential linear augmented plane-wave method in our calculations by Wien2k code. Results have been compared with other computational and experimental data for similar systems. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, WIEN2k package has been used to calculate the structural and magnetic characteristics, and the hyperfine fields in a series of 1:1 ordered iron binary alloys and intermetallics FeT (T = Ti, V, Cr, Mn, Co, Ni). This is done by solving Kohn-Sham equations using the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method. In the calculations, the Local Spin Density Approximation (LSDA) and the Generalized Gradient Approximation (GGA) were used for comparison. The results were compared with other theoretical and experimental measurements. Based on our results, GGA is found to be better than the LSDA in evaluating the hyperfine fields. Also the hyperfine fields in the ordered phases were found to be smaller than the hyperfine fields in the disordered phases of the studied systems. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The electronic structure of four polytypes (beta, gamma, delta and epsilon) of hexagonal GaSe and InSe is calculated from first principles, using the WIEN2k and VASP codes and PBEsol prescription for the exchange-correlation potential, aiming specifically at elucidating the crystallographic parameters and comparing the energy placement of corresponding competing structures. Further on, the compounds with different composition of the same constituents, namely the ordered-vacancies systems Ga2Se3 and In2Se3, were subject to a similar study, of which the relaxed crystal structure data for three different phases is reported. Comparison is done with the nomi- nal wurtzite structure over which the cation vacancies are introduced, and the relaxation pattern discussed.

The complex density functional theory (DFT) calculations of structural, electronic, linear and nonlinear optical properties for the defect chalcopyrite CdAl2Se4 compound have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2k code. We employed the Wu and Cohen generalized gradient approximation (GGA-WC), which is based on exchange–correlation energy optimization to calculate the total energy. Also we have used the Engel–Vosko GGA formalism, which optimizes the corresponding potential for band structure, density of states and the spectral features of the linear and nonlinear optical properties. This compound has a wide direct energy band gap of about 2.927 eV with both the valence band maximum and conduction band minimum located at the center of the Brillouin zone. The ground state quantities such as lattice parameters (a, c, x, y and z), bulk modulus B and its pressure derivative B′ are evaluated. We have calculated the frequency-dependent complex e ( ω ) , its zero-frequency limit e 1 ( 0 ) , refractive index n ( ω ) , birefringence Δ n ( ω ) , the reflectivity R ( ω ) and electron energy loss function L ( ω ) . Calculations are reported for the frequency-dependent complex second-order nonlinear optical susceptibilities. We find opposite signs of the contributions of the 2ω and 1ω inter/intra-band to the imaginary part for the dominant component through the wide optical frequency range.

Electronic properties of cadmium selenogallate CdGa2Se4, a very promising electro-optical material, were studied both from theoretical and experimental points of view employing the ab initio band-structure augmented plane wave + local orbitals (APW + LO) method with the WIEN2k code and X-ray photoelectron spectroscopy (XPS). The present APW + LO calculations reveal that the Se p-like states are the dominant contributors into the top of the valence band of CdGa2Se4, while the bottom of the band is dominated by contributions of the Cd d-like states. Additionally, the bottom of the conduction band of the compound under consideration is dominated by contributions of the Ga s-like states. The present calculations render that the valence-band maximum and conduction band minimum in CdGa2Se4 are located at Γ resulting in a direct energy gap. The imaginary part of the electronic dielectric function ɛ(ω) was also calculated for the compound under consideration based on its band-structure data. The ɛxx(ω) and ɛzz(ω) components of the imaginary part of the electronic dielectric function reveal a considerable anisotropy in CdGa2Se4. The XPS valence-band spectrum of CdGa2Se4 has been derived and the binding energies of core-level electrons of the constituting atoms of the compound have been measured.

The first-principles energetics of the constituent elements Ca and Mg and the Mg2Ca C14 laves phase (C14) in the Ca–Mg binary system were used in the computational thermodynamic modeling, with models for the Gibbs energy of individual phases. C14 was modeled as (Ca,Mg)2(Ca,Mg)1 with four end-members. The first-principles calculations were performed using two computer codes: (i) WIEN2K based on the full-potential linearized augmented plane-wave (FLAPW) method and (ii) VASP based on the pseudo-potentials and a plane wave basis set. The total energies of the pure Ca and Mg in the fcc, bcc, and hcp structures, three laves phase structures of Mg2Ca, and the four end-members of C14 were calculated at 0 K. The enthalpies of formation of the four end-members were obtained accordingly and used as input data in evaluating the Gibbs energy functions of C14. The entropy contribution in the Gibbs energy function for C14 was obtained through its liquidus data. Special quasirandom structures are used to mimic random mixing in the C14 laves phase for two compositions, i.e. (Mg)2(Ca0.5,Mg0.5) and (Ca0.5,Mg0.5)2(Ca). The complete thermodynamic description of the Ca–Mg binary system with C14 modeled as a solution phase was obtained by this combined computational thermodynamics/first-principles approach showing a good agreement with experimental data and previous modeling in the literature.

We present an ab initio density functional study of magnetic phase transitions in the YCo3H2 system. The augmented plane wave and local orbital method as employed in the WIEN2K code is used to predict the structure and electronic structure of this compound. Comparison is made with recent X-ray diffraction and magnetization studies. The calculations suggest that the YCo3H2 system is ferrimagnetic in character. Further, fixed spin moment calculations are used to predict and interpret magnetic phase transitions observed in externally applied magnetic fields.