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NiTi alloy has important properties such as shape-memory, super-plasticity, resistance, and biocompatibility, therefore is frequently used in biomedical devices. We studied the oxidized form of this alloy and possible Ni segregation in three possible models for the TiO/NiTi interface: i) the perfect interface; ii) the Ni enriched interface and iii) with oxygen vacancies in the TiO coating. We used DFT + U calculations for TiO, because Hubbard correction encourages localization of the excess electronic charge and improves the DFT results. A standard spin polarized DFT was used for NiTi. We obtained the optimized geometries for each model and computed segregation energy, electronic structure, magnetic moment and bond order for the interface and for Ni segregation. Our calculations indicated that Ti species are present at the interface, while in the bulk of the oxide layer the species is the Ti. Also, the electronic structure show that the metallic character of the alloy is unaffected by the interaction with oxygen. These results are consistent with experimental data from literature. Ni enriched interface containing O vacancies show a strong geometric distortion in the TiO layers. In all cases, Ni segregation is an a thermodynamically unfavorable process, helping to understand the biocompatibility of NiTi alloy., Our work was supported by ANPCyT through PICT 2016 Raíces N° 2016-4085 Res. N° 285/16 and PICT 2016 N°2016-4094 Res. N° 285/16 research grants, as well as by SGCyT-UNS. PB, EAG and PVJ are members of CONICET. JJ, MS and VO are fellow researchers at this institution. In addition, AHL and CISD acknowledge the Spanish MINCINN project grants FIS2016-77692-C2-2P and PCIN-2017-098, along with FEDER European funds. Calculations have been performed in the Alhambra Computing Center of University of Granada and in the CSIC Computational Center. Particularly, we acknowledge to Dr. Santiago Melchor Ferrer from University of Granada.

This work presents a theoretical study, based on DFT calculations, about the changes induced when diatomic molecules (CO, O2 and H2) are adsorbed on defective (8,0) SWCNT doped with a Li atom. The adsorption of one Lithium atom is tested inside and outside of the nanotube containing a single vacancy. The Li atom induces a magnetic moment on the nanotube and an important reduction in its the band gap (Eg). The adsorption energy values (Eads) for CO, O2 and H2 when Li is located inside, are higher than when Li is outside. The H2 adsorption does not change the magnetic nature of the system. However, the CO and O2 molecules reduce the magnetic moment from 1.0 µB to 0.0 µB. The band gap energy is reduced for CO and O2, while increases in the case of H adsorption. The work function (WF) value is reduced in the cases of CO and H2; whereas for O2 we observed an opposite behavior, then the final charge state of this molecule is negative. Based on our results, the system Li + defective (8,0) SWCNT can be proposed as possible candidate as gas sensor of CO,O2 and H2. Fil: Luna, Carla Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Bechthold, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Brizuela, Graciela Petra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Pistonesi, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina

We performed density functional calculation of the acetylene hydrogenation reaction on the PdGa(110) surface. The reaction C 2 H 2 +H 2 → C 2 H 4 is modeled and understood in terms of chemical bonding change. The evolution of electronic structure and electron density plot also shed more light on the role of Pd, Ga and C 2 H 2 during the hydrogenation reactions. This new way of looking at a particular chemical reaction includes the changes in bond order in the different reaction steps. As mentioned before the role of Ga is revealed as a part of the active site and not a single spacer. Fil: Sandoval, Mario German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Bechthold, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Orazi, Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Gonzalez, Estela Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Jasen, Paula Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina

In this work, Li doped TiO2(B) was modelled throughout the implementation of density functional theory with Hubbard methodology (DFT + U) in order to understand its vibrational and thermodynamics properties. Firstly, we performed structural, electronic structure and charge density difference studies in order to find accurately modelled systems. The electronic structure analysis shows that the lithiated systems have a metallic character and a n-type behavior, also the asymmetric DOS reveals that a small induced magnetic moment is present. The charge density difference analysis confirmed that the charge transfer is from the Li to the oxide. The vibrational properties studies present the undiscovered irreducible representation of the Li-TiO2(B) systems and its phononic densities. Moreover, the Raman spectroscopy studies of the bulk show great correspondence with experimental literature and the novel spectra obtained of the doped systems show a dispersion and displacement of the peaks. Additionally, the thermodynamic properties studies show evidence that both doped systems show promising features. Therefore, the results obtained here are innovative and can be used as reference connected with future experimental studies of this material, which has potential to be employed as a Li-ion battery anode.

TiO2(B) has potential as an anode material for Li-ion batteries. Although theoretical and experimental studies related to the intercalation of Lithium (Li) in TiO2(B) already exist, to the best of our knowledge there are no studies in the open literature related to Li intercalation in low-index surfaces of this oxide phase. Therefore, we study the intercalation of Li in the (100) and (001) surfaces of TiO2(B) using Density Functional Theory (DFT). The DFT + U Hubbard methodology was included to consider the strong correlation of the “d” electron states of the transition metal. Electronic densities of states of the surfaces were analyzed in the diluted limit concentration of Li. We found a small-induced magnetic moment present. The diffusion of Li atoms in the surfaces was studied using the Nudged Elastic Band (NEB) method. Our results indicated that the Li intercalation in the (100) and the (001) surfaces is a favorable process. Moreover, we found diffusion pathways energetically stables for both surfaces. Calculations of charge density difference with Li intercalated in the energetically stable positions on the surfaces indicate that the charge density on Li is a local phenomenon and a charge transfer occurs from Li to the nearest Ti and O atoms.

The Se adsorption at different coverages on DO3 FeSiAl(110) surface is studied using density functional theory (DFT). Se adsorption is favorable in almost all surface high-symmetry sites, except for the bridge site formed by Fe–Si atoms. The most stable is a hollow site formed by four Fe atoms with adsorption energy of −5.30 eV. When the coverages increase, the energies decrease in the case of hollow sites. The surface present a reconstruction after Se adsorption, being the most important at 1/2 ML. The local magnetic moment for Fe atoms increase for the type A (all nearst neighbours (nn) are Fe atoms) and decrease for the type B (nn are Fe, Si and Al atoms). The most affected metal orbitals are Fe 4s and 4p. In the case of the hollow site the surface Fe–Fe bond is weakened after Se adsorption. A Fe–Se bond is developed at all coverages in both sites being the most important on top (dFe–Se = 2.23 A, OP: 0.774 at 1/4 ML). The first and second layer Fe–Fe bond increase at 1/4 ML and decrease at 1/2 and 1 ML. Small Se–Se bonding interaction appear at 1/2 ML and increase noticeable for 1 ML. For the top site, the Se–Se bond appears at all coverage. The Fe–Fe surface bonds also decrease its strength with respect to the clean surface at all coverage. The first and second layer Fe–Fe bond increase at all coverage.

Se adsorption on Fe(1 0 0) and (1 1 1) surfaces is examined using the density functional theory (DFT). Selenium is adsorbed in a distorted bridge on the (1 1 1) surface while in the (1 0 0) surface it prefers a 4-fold hollow site, with energies of -10.36 and -5.25 eV, respectively. Se adsorption results in surface reconstruction. There is some contraction in the case of the (1 0 0) plane for 1/4 and 1/2 ML coverage and some relaxation at 1 ML (4.5%). Contraction increases to 15% for the (1 1 1) plane at 1/4 ML. At a higher coverage, there is a non-regular movement of surface metal atoms, and there is almost no change at 1 ML. The magnetic moment for surface Fe atoms decreases with coverage. The most important changes are in the (1 0 0) plane, followed by the (1 1 0) and then the (1 1 1) planes with a reduction of 52%, 24% and 7% respectively. The density of states presents a contribution of Se states at -5.0 and -13.1 eV, when stabilized after adsorption. The Fe-Fe bond weakening is higher in the (1 0 0) plane. Fe-Se bonds are formed at the expense of the metallic bond. Fil: Cardoso Schwindt, Virginia Araceli. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Ardenghi, Juan Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Bechthold, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Gonzalez, Estela Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Jasen, Paula Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Batic, Barbara Setina. Institute of Metals and Technology; Eslovenia Fil: Jenko, Monika. Institute of Metals and Technology; Eslovenia

Fil: Bechthold, Pablo Ignacio. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto de Fisica del Sur. Universidad Nacional del Sur. Departamento de Fisica. Instituto de Fisica del Sur; Argentina

Co-adsorption of benzene and CO on PtCo(1 1 1) surface at low coverage is studied using density functional theory calculations. We investigated the PtCo FCT alloy surface with a uniform distribution. The most favorable site for CO is top on a Pt atom whereas for benzene is an HCP hollow site (formed by 2 Pt atoms and 1 Co atom). The co-adsorption energy is -1.62 eV. The calculations indicate a CO molecule with a ∼4 tilt angle with the normal to the surface. The most important bond is PtC CO , as revealed by overlap population analysis. A very small CO-benzene interaction is also detected. The vibrational frequencies of adsorbed benzene and CO were also computed. Fil: Orazi, Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Bahía Blanca. Instituto de Física del Sur; Argentina; Fil: Ardenghi, Juan Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Bahía Blanca. Instituto de Física del Sur; Argentina; Universidad Nacional del Sur. Departamento de Física; Argentina; Fil: Bechthold, Pablo Ignacio. Universidad Nacional del Sur. Departamento de Física; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Bahía Blanca. Instituto de Física del Sur; Argentina; Fil: Jasen, Paula Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Bahía Blanca. Instituto de Física del Sur; Argentina; Universidad Nacional del Sur. Departamento de Física; Argentina; Fil: Pronsato, Maria Estela. Universidad Nacional del Sur. Departamento de Física; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Bahía Blanca. Instituto de Física del Sur; Argentina; Fil: Gonzalez, Estela Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Bahía Blanca. Instituto de Física del Sur; Argentina; Universidad Nacional del Sur. Departamento de Física; Argentina

The adsorption of atomic Se on a Fe(1 1 0) surface is examined using the density functional theory (DFT). Selenium is adsorbed in high-symmetry adsorption sites: the -short and long-bridge, and atop sites at 1/2, 1/4, and 1 monolayer (ML) coverages. The long bridge (LB) site is found to be the most stable, followed by the short bridge (SB) and top sites (T). The following overlayer structures were examined, p(2 × 2), c(2 × 2), and p(1 × 1), which correspond to 1/4 ML, 1/2 ML, and 1 ML respectively. Adsorption energy is −5.23 eV at 1/4 ML. Se adsorption results in surface reconstruction, being more extensive for adsorption in the long bridge site at 1/2 ML, with vertical displacements between +8.63 and −6.69% -with regard to the original Fe position-, affecting the 1st and 2nd neighbours. The largest displacement in x or y -directions was determined to be 0.011, 0.030, and 0.021 A for atop and bridge sites. Comparisons between Se-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the Se. At the long bridge site, the presence of Se causes a decrease in the surface Fe d-orbital density of states between 4 and 5 eV below Fermi level. The density of states present a contribution of Se states at −3.1 eV and −12.9 eV. stabilized after adsorption. The Fe–Fe overlap population decrease and a Fe–Se bond are formed at the expense of the metallic bond.