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Methanesulfonic acid (CH3SO3H), also known as MSA, has been found to be capable of forming a strong hydrogen-bonded interaction with sulfuric acid (H2SO4) under ambient conditions. The energetic stability of the MSA···H2SO4 clusters increases with decreasing temperature at higher altitudes in the troposphere, which is relevant in the context of atmospheric aerosol formation. We have performed, in the present work, a detailed and systematic quantum-chemical calculation with high-level density functional theory to characterize the hydrogen bond formation in the binary MSA···H2SO4, ternary MSA···(H2SO4)2, and quaternary MSA···(H2SO4)3 clusters. The five different conformations of MSA···(H2SO4)2 and six conformations of MSA···(H2SO4)3, considered in the present work for the spectroscopic analysis, have been taken from our previous work [J. Phys. Chem. A. 2020,124, 11072-11085]. The hydrogen bonds were analyzed on the basis of infrared vibrational frequencies of different O-H stretching modes and quantum theory of atoms in molecules (QTAIM). A strong positive correlation has been observed between the red shift of the OH groups in MSA and H2SO4 and the corresponding O-H elongation as a result of hydrogen bond formation. Topological analysis employing QTAIM shows that most of the charge density and the Laplacian values at bond critical points (BCPs) of the hydrogen bonds of the MSA···(H2SO4)n (n = 1-3) complexes fall within the standard hydrogen-bond criteria. However, those outside these criteria fall in the category of a very strong hydrogen bond with a hydrogen bond length as low as 1.41 A and an O-H bond elongation as high as 0.096 A. In general, the charge densities of the BCPs located on hydrogen bonds increase as the hydrogen-bond lengths decrease. Proportionately, a larger number of hydrogen bonds in ternary MSA···(H2SO4)2 demonstrate a partial covalent character when compared with the quaternary clusters.

A nanostructured defect-fluorite-type Sm3NbO7 has been produced at ambient temperature by the process of mechanical alloying (MA). The powdered mixture of samarium precursor and pure metallic Niobium (Nb) is milled for 17h to obtain the desired sample with mean crystallite size of 160 A. The phase transformations induced by the high energy milling have been investigated by ex situ X-Ray Diffraction (XRD) measurements and Rietveld method. The results suggest a symmetrization of Sm(OH)3 crystals induced by Nb solubilization. The Sm3NbO7 microstructures have been examined by Differential Scanning Calorimetry (DSC), heat treatment, Raman spectroscopy and Density Functional Theory (DFT) calculation. The crystallite sizes and defects have been analyzed by Line Profile Analysis utilizing Williamson Hall plot method and Stephens's microstrain model. The anisotropic structural defects caused by MA synthesis disappear under heat treatment with the microstrain reducing from 1.4% to 0.05%.

Density functional theory calculations are used to investigate a series of zigzag and armchair nanotubes of carbon, boron and nitrogen with various values of tube diameters. The nanotubes are studied to understand the effect of the diameter values and the chirality on the energetics, structure and electronic properties of nanotubes. Depending on the composition we observe metallic behavior to be predominant in the nanotubes of carbon-boron (CBNT) and carbon-nitrogen (CNNT). However, semiconducting behavior is observed for the nanotubes of boron-nitrogen (BNNT). The stability of the nanotubes is found to be dependent on the respective chiralities.

A nanostructured solid solution of SnSe1−xSx with x = 0.5 synthesized by mechanical alloying and its structural stability was studied by calorimetric measurements under high pressure conditions. The structural behavior under pressure was investigated using angle-dispersive X-ray diffraction in a synchrotron source and first-principles density functional theory (DFT) calculations. The variations of the cell structure phases were described by a third-order Birch–Murnaghan equation of state.

The tunneling rate of a particle between two sites situated in different sublattices of a single-layer graphene sheet which can interact with the conduction electrons has been calculated. The interaction between the impurity sites is decisive in determining the tunneling rate. Furthermore, the rate also depends on the energy of the impurities along with value of the chemical potential of the system.

We study the formation of local moments in a metallic host due to a localized spin-orbit (Rashba) interaction. Using the Anderson model we describe the occurrence of magnetic moments through calculation of the magnetic-non-magnetic phase transition within the mean-field scenario. We compare our results with those in the absence of the Rashba interaction. The symmetry and regime of the magnetic phase demonstrates a dependence on the above interaction. The conductance values through the impurities are also exhibited for the above phases.

Density functional theory calculations have been used to investigate the adsorption of H atom and small molecules (H 2 , O 2 , N 2 , CO, CO 2 , NO and NO 2 ) on the surface of the zigzag and the armchair boron-nitrogen nanotubes. The adsorptions are considered both at the nitrogen and boron sites of the nanotubes. The structural parameters, binding energies, intramolecular bond-lengths and the band gaps are analyzed to understand the adsorption properties of the complexes. Furthermore, density of states (DOS), band structures and charge-density transfer calculations are also performed. Among all the constituents, the adsorption of the hydrogen atom on both versions of the pristine boron-nitrogen nanotubes demonstrates the highest stability.

The indirect nuclear spin–spin coupling constants of homogeneous hydrogen-bonded HCN clusters are compared with those of inhomogeneous HCN clusters where one of the terminal HCN molecules i...

The Sn-Se based materials were synthetized by mechanical alloying and simple melting techniques. By mechanical alloying technique we observed a very fast nucleation of the SnSe orthorrombic layered compound with a remarkable structural stability. On the other hand, the milling atmosphere showed a strong influence on the final result. By simple melting of the elemental Se and Sn powders we obtained a very oriented SnSe layered structures. The microstructural details were evaluated by Stephens's microstrain model, differential scanning calorimetry and thermic treatment.

Made available in DSpace on 2018-12-11T17:15:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The electronic structure and transport properties of a single layer of graphene (Gr) on α-Al2O3 surface are studied using the density functional theory (DFT). We present three models that take into account the atom at the termination of the alumina surface: a) Al atoms, with the center of the Gr hexagon directly over an Al atom; b) Al atoms, with a carbon directly positioned above an Al atom; c) oxygen atoms. Two processes of geometric optimization were used: (i) All the atoms of the supercell were allowed to move in accordance with the BFGS quasi-Newton algorithm; (ii) The atoms of the three topmost layers of the α-Al2O3 (0001) slab, including the C atoms, were allowed to move, whereas the atoms of the remaining layers were frozen in their respective atomic bulk positions. The first two models preserve qualitatively the electronic structure of the pristine Gr using the geometric optimization process (i) whereas, in the third model this structure was lost due to a significant charge transfer between the carbon and oxygen atoms irrespective of the optimization procedure. However, models (a) and (b) with the optimization (ii) reveal a p-type semiconducting behavior. Department of Physics Federal University of Amazonas São Paulo State University(Unesp) Institute for Theoretical Physics (IFT) São Paulo State University(Unesp) Institute for Theoretical Physics (IFT)

The adsorption of two kinds of cellulose chains on graphene and boron-nitride (insulating and semi-conducting) sheets were studied using first principles density-functional theory calculations. The effect of adsorption was analyzed in terms of the binding energy, band-structure, density of states, charge density differences and current behavior. The stable conformations demonstrate the possibilities of creating bio-conducting materials important for various applications utilizing cellulose, one of the most abundant biopolymers in nature. The charge-density differences reveal the charge accumulation on the atoms of the substrates/cellulose depending on the type of atom. Moreover, the increase in conductivity of the combined systems compared to the biopolymer as is evident from the current vs bias voltage study indicates the conducting nature of the systems.

Graphene-like ZnX (X=O, S, Se, Te) structures are studied using the DFT+U method to address in detail the questions regarding the dynamical stability and also their utility in optoelectronic devices. The layer modulus, the Young's modulus, the shear modulus, and the Poisson coefficient demonstrate the stability of all ZnX in the presence of the Hubbard parameter U. Cohesion energy calculations show ZnO to be the most stable one and ZnSe to be the least stable one among the four systems. The presence of a direct bandgap in all the systems makes them suitable for use in optoelectronic devices. The gap values range between 2.13 eV in ZnTe and 3.50 eV in ZnO. U values tend to increase the bandgap in all the systems. This increase is seen to be as high as 100% in ZnO. A detailed study of the band structure and partial density of states is carried out. The electronic, optical, and thermoelectric properties of the ZnX monolayers are exhibited. The superior limit of the figure of merit increases with temperature and the highest value is found to be of the order of 0.6 in ZnO at 900 °C. Overall, the inclusion of the Hubbard parameter demonstrates better stability and also its importance in technological applications.

In this work we use ab initio density functional theory (DFT) and propose three new configurations of substituted graphene monolayers where the carbon atoms are replaced selectively by boron and nitrogen. The stable equilibrium geometries and corresponding structural, electronic and transport properties of the resulting graphene-like BC, NC and BN hexagonal single-atomic-layer compounds are determined. The characteristics of the NC and BC new compounds are found to be metallic. Our proposed boron-nitrogen hexagonal structure behaves as a semiconductor with gap of 0.52 eV, while the h -BN (alternating boron and nitrogen in graphene structure) studied so far widely is typically an insulator or a wide-band semiconductor. The value of electric current in BC structure is found to be higher than that in usual graphene for a given value of the bias voltage.

The synthesis of a nanometric and monophasic SmAlO3 perovskite by utilizing the process of mechanical alloying at room temperature is reported for the first time. The structural evolutions are examined by the ex-situ X-Ray diffraction measurements, which demonstrate that the perovskite nucleation occurs on 2 ​h of milling, and its phase fraction increases proportionally with the processing time. Thermal stability analysis is performed in order to accomplish the annealing at 1050 ​°C. The obtained sample is found to be orthorhombic with nanometric crystallites of 41 ​nm. The optical and vibrational properties of the prepared SmAlO3 sample have been investigated by Raman and UV–Vis measurements along with DFT calculations. The SmAlO3 Raman peaks are appropriately assigned to the fundamental vibrational modes and an excellent agreement between the experimental and theoretical Raman modes is observed. The vibrational modes, band gap, density of states and the energy bands are also demonstrated.

We study the behavior of a quantum dot attached to two electrodes with localized spin–orbit (Rashba) interactions. Using the Anderson model we report the occupation number, specific heat, susceptibility and conductance in the zero-band width limit. We compare our results with those in the absence of the Rashba interactions. The symmetry and regime of various phases demonstrate a strong dependence on the above interactions.

Density functional theory calculations have been used to investigate the adsorption of glycine molecule on the zigzag and armchair single-walled boron-nitrogen nanotubes. The functional groups of glycine were used to interact with the surface of (5,0) and (5,5) nanotubes through nitrogen, the more electronegative atom of the nanotube. The structural parameters, binding energy, strain energy, charge-density transfer and the band gap were used to understand the binding properties of the complexes. The adsorption of glycine through the O H group is found to be the most stable for both the (5,0) and (5,5) structures. Furthermore, density of states (DOS), band structures, the highest occupied orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) were also exhibited to illustrate the adsorption mechanism.

Density Functional Theory (DFT) calculations have been performed to study the effect of the hydrogen bond formation on the Nuclear Magnetic Resonance (NMR) parameters of hydrogen-bonded clusters of glycine molecules in gas-phase. DFT predicted isotropic chemical shifts of H, C, N and O of the isolated glycine with respect to standard reference materials are in reasonable agreement with available experimental data. The variations of isotropic and anisotropic chemical shifts for all atoms constituting these clusters containing up to four glycine molecules have been investigated systematically employing gradient corrected hybrid B3LYP functional with three different types of extended basis sets. The clusters are mainly stabilized by a network of strong hydrogen bonds among the carboxylic (COOH) groups of glycine monomers. The formation of hydrogen bond influences the molecular structure of the clusters significantly which, on the other hand, gets reflected in the variations of NMR properties. The carbon (C) atom of the COOH group, the bridging hydrogen (H) and the proton-donor oxygen (O) atom of the O H bond suffer downfield shift due to the formation of hydrogen bond. The hydrogen bond lengths and the structural complexity of the clusters are found to vary with the number of participating monomers. A direct correlation between the hydrogen bond length and isotropic chemical shift of the bridging hydrogen is observed in all cases. The individual variations of the principal axis elements in chemical shift tensor provide additional insight about the different nature of the monomers within the cluster.

authoren The effects of the spin–orbit couplings (SOC) including the Rashba and the Dresselhaus interactions are considered for the high cuprates with superconducting gap (DSC) and the pseudogap (d-density wave, DDW) phase. The sole Rashba or the Dresselhaus interaction is shown to have a stronger effect on the superconducting phase when compared to the mixed SOC. The temperature dependencies of the DSC and DDW parameters along with the specific heat of both the underdoped and the overdoped cuprates were considered.

The pressure-induced phase transitions in nanostructured SnSe were investigated using angle-dispersive X-ray diffraction in a synchrotron source along with first-principles density functional theory (DFT) calculations. The variation of the cell parameters along with enthalpy calculations for pressures up to 18 GPa have been considered. Both the experimental and the theoretical approaches demonstrate a phase transition at around 4 GPa. Below 8.2 GPa the X-ray diffraction patterns were fitted using the Rietveld method with space groupPnma(No. 62). The lattice parameters and atomic positions for the above-mentioned symmetry were used in DFT calculations of thermodynamic parameters. The enthalpy calculations with the computationally optimized structure and the proposedPnmastructure of SnSe were compatible. The variations of the cell volume for the high-pressure phases are described by a third-order Birch–Murnaghan equation of state.

The present study investigates the pressure dependencies of the structural and the thermoelectric properties of the half-Heusler alloys NiTiZ (Z = Si, Ge, Sn and Sb) using the first-principle density functional study. The fully relaxed samples demonstrate a semiconducting characteristic with an increase of the energy-gaps in NiTiZ (Z = Si, Ge and Sn) with pressure whereas the metallic character prevails in NiTiSb throughout the entire range of the pressure considered. The computed equilibrium lattice constants are in excellent agreement with the available experimental and theoretical data. A detailed calculation and analyses of the thermoelectric properties of the above half-Heuslers have been performed. Moreover, among the above half-Heuslers, the dimensionless figure of merit of the semiconducting alloys is maximum for NiTiSn. In case of NiTiGe, we observe a gradual increase in its figure-of-merit value with pressure.

Made available in DSpace on 2018-11-26T17:52:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-06-08 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) We report theoretical analysis of charge transport process through a single glycine molecule utilizing graphene nanogaps. Density functional theory and non-equilibrium Green's function method are employed to investigate the transport properties of glycine inside the gap. The projected density of states, transmittance, and the current-voltage characteristics are determined with changes in the molecular orientation inside the nanogap of c.a 0.8 nm. The current values demonstrate a high sensitivity on the orientation of the molecule. The conductance of the molecule is also dependent on the voltage. Univ Fed Amazonas, Dept Phys, BR-69077000 Manaus, Amazonas, Brazil Univ Fed Amazonas, Dept Math, BR-69077000 Manaus, Amazonas, Brazil Univ Sao Paulo, Inst Phys, BR-05508090 Sao Paulo, SP, Brazil Sao Paulo State Univ, Inst Theoret Phys, Sao Paulo, SP, Brazil Sao Paulo State Univ, Inst Theoret Phys, Sao Paulo, SP, Brazil

Made available in DSpace on 2018-11-26T17:48:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-05-15 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The formation of the localized magnetic moments is studied due to the presence of two-impurities in the two sublattices of a single-layer graphene sheet. The interaction between two similar magnetic impurities and also the hybridizations are decisive in determining the boundary between the magnetic and the non-magnetic states. A strong chemical potential dependence of the above phase boundary is evident. An anomalous scaling of the boundary separating the above regions is more pronounced in the two-impurity case when compared to that of the single impurity. (C) 2018 Elsevier B.V. All rights reserved. Univ Fed Amazonas, Dept Phys, BR-69077000 Manaus, Amazonas, Brazil Sao Paulo State Univ, Inst Theoret Phys, Sao Paulo, SP, Brazil Sao Paulo State Univ, Inst Theoret Phys, Sao Paulo, SP, Brazil

The influence of the hydrogen-bond formation on the NMR spin–spin coupling constants, including the Fermi contact, the diamagnetic spin–orbit, the paramagnetic spin–orbit and the spin dipole term, has been investigated for the ortho-aminobenzoic acid microhydrated with up to three water molecules. The one-bond and two-bond spin–spin coupling constants for several intra-molecular and across-the-hydrogen-bond atomic pairs are calculated employing high-level density functional theory in combination with the B3LYP functional with two different types of extended basis sets for each level of microhydration. The spin–spin coupling constants, in general, vary inversely with the hydrogen bond length. The Fermi contact term is found to be the dominant contributor to the total value of spin–spin coupling constant followed by the paramagnetic spin–orbit term. The variations of Fermi contact term and atomic charge distribution with size of microhydration follow quite similar trend. The effect of explicit solvation pro...

Spin caloritronics, the combination of spintronics with thermoelectrics, exploiting both the intrinsic spin of the electron and its associated magnetic moment in addition to its fundamental electronic charge and temperature, is an emerging technology mainly in the development of low-power-consumption technology. In this work, we study the thermoelectric properties of a Rashba dot attached to two single layer/bilayer graphene sheets as leads. The temperature difference on the two graphene leads induces a spin current, which depends on the temperature and chemical potential. We demonstrate that the Rashba dot behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the chemical potential, temperature, and also the Rashba term have been observed.

The influence of the hydrogen bond formation on the nuclear magnetic resonance parameters has been investigated in the case of microhydrated ortho-aminobenzoic acid (o-Abz) in the gas-phase. DFT-B3LYP/aug-cc-pVDZ predicted 1H and 13C isotropic chemical shifts with respect to TMS of the isolated o-Abz are in reasonable agreement with available experimental data. The isotropic and anisotropic chemical shifts for all atoms of o-Abz within the o-Abz ··· (H2O)1-3 complexes have been calculated at the Hartree–Fock, and density functional (B3LYP) theoretical levels using the 6-31++G(2d,2p) and aug-cc-pVDZ basis sets and considering the counterpoise corrections for the basis set superposition errors. The chemical shift values of the carboxyl group atoms of microhydrated o-Abz relative to isolated o-abz do not show significant basis set dependence. Both the hydrogen and carbon atoms constituting the carboxyl group of o-Abz suffer downfield shift due to formation of hydrogen bond with water. The length of hydrogen b...

The ESR of a magnetic probe sited at a distance R from an adatom in graphene, interacting via a RKKY interaction, is studied. The spin relaxation rate of the magnetic probe in the case of pristine graphene satisfies a T(3) dependence for all temperatures at the Dirac point. However, away from the Dirac point a T(3) dependence is observed only for high temperatures unlike the Korringa behavior at low temperatures. Moreover, the zero-temperature relaxation rate of the pristine graphene demonstrates a quadratic dependence on the chemical potential. In the presence of the magnetic adatom hybridized with one site of the graphene sublattice we observe a dip in the relaxation rate away from the Dirac point. At the Dirac point a deviation from the T(3) dependence is observed. The presence of the Coulomb interaction U also modifies the zero-temperature relaxation rate when compared to that of pristine graphene. The transition from the magnetic state to the non-magnetic state is also characterized by a minimum in the relaxation rate.

The effect of non-magnetic impurity-scattering is considered on the asymmetric superconducting gap (SC) and the d -density wave (DDW) phase of the high T c cuprates. The phase diagrams for the cuprates demonstrate that T c decreases with scattering potential and is most affected in the coexisting phase of DDW and SC orders. Moreover, the SC gap to T c ratio increases with doping and impurity scattering. The transition temperature of the DDW state, T ∗ also decreases with scattering. The density of states in the mixed SC + DDW state for the underdoped (UD) phase, SC state in the overdoped phase and the DDW state in the UD phase, also suffers a modification. Its effect on specific heat results is also discussed. The increase in the gap to T c ratio and the specific heat are also observed in the presence of the non-magnetic impurities. A suppression in the superfluid density is found with the increase in impurity.

The NMR relaxation rate is studied on the magnetic states of an impurity in bilayer graphene within a tight-binding scenario. The dependencies of the relaxation rate on temperature, interlayer interaction and also the chemical potential have been considered. Although for low temperatures we observe the usual Korringa relation, a characteristic of the conventional fermions, the rate increases with the increase in temperature and tends to saturate for high temperatures. For small interlayer interactions ( t ⊥ ) the system can be either magnetic or non-magnetic. However for higher t ⊥ we observe the existence of only a pure magnetic state. In graphene this transition is also observed with two cusps related to the magnetic to non-magnetic transition, which modifies to a single hump for higher t ⊥ , where the system is purely magnetic for any value of chemical potential.

The q -deformed algebraic method based on the extension of the number concept as proposed by Gauss [1] is used to obtain a q -analog to the gap equation for the cuprates using a tight-binding model. The conventional s -wave symmetry along with the d x 2 - y 2 wave order parameter are considered to understand the effect of q -fermionic theory which is a generalization or deformation of the usual Fermi theory. The dependence of the gap and/or the critical temperature on doping for various values of q is studied. Specific heat and the phase diagram are found to be explicitly dependent on the parameter and the well-known hump-like behavior is detected for q > 1. Moreover, the position of the maximum in T c in the phase diagram depends on the value of q and also on the value of the coupling.

The effect of aperiodicity on the charge transfer process through DNA molecules is investigated using a tight-binding model. Single-stranded aperiodic Fibonacci polyGC and polyAT sequences along with aperiodic Rudin–Shapiro poly(GCAT) sequences are used in the study. Based on the tight-binding model, molecular orbital calculations of the DNA chains are performed and ionization potentials compared, as this might be relevant to understanding the charge transfer process. Charges migrate through the sequences in a multistep hopping process. Results for current conduction through aperiodic sequences are compared with those for the corresponding periodic sequences. We find that dinucleotide aperiodic Fibonacci sequences decrease the current while tetranucleotide aperiodic Rudin–Shapiro sequences increase the current when compared with the corresponding periodic sequences. The conductance in all cases decays exponentially as the sequence length increases.

The effects of the spin-orbit coupling are considered for the high T c cuprates with asymmetric superconducting gap (SC) and the d-density wave (DDW) phase due to its vital role in the experimental determination of the DDW state. Experiments predict an anisotropy in the DSC gap where |Δ(0,π)|>|Δ(π,0)| and the gap node deviates from the diagonal direction towards the k x axis. Measurements also demonstrate DDW to be a possible candidate for the pseudogap in the underdoped phase. Due to the spin-orbit (SO) coupling in the low temperature orthorhombic (LTO) phase, the phase diagram of the cuprates suffers a change due to the modification of the T* value, the temperature characteristic of pseudogap, although T c remains unaltered. Moreover, for a more generalized SO coupling, the DDW gap decreases with the angle but has no effect on the SC gap. We calculate the density of states in the various regimes of doping for the mixed SC+DDW states in the underdoped (UD) phase, SC state in the overdoped phase and also the DDW state in the UD phase and compare them with various theoretical and experimental works. The temperature dependence of the specific heat does not exhibit any qualitative change due to the SO coupling.

The asymmetric gap superconductivity is considered in orthorhombic high Tc cuprates. Recent experiments predict an anisotropy in the gap where |Δ(0,π)|> |Δ(π,0)| and the gap node deviates from the diagonal direction toward the kx axis. The temperature dependencies of the specific heat and penetration depth along the a and b directions are calculated for the anisotropic gap superconductors. However, the anisotropy in the penetration depth can be consistent with the experimental observations only after the inclusion of the plane and chain coupling. The d-density wave (DDW) phase that explains the pseudogap has also been considered to study the phase diagrams of the cuprates.

We present the in-plane and c-axis penetration depths of the underdoped cuprates. The pseudogap phase is addressed within the framework of the ordered d-density wave (DDW). The above scenario is considered using a mean-field calculation of the tight binding model which incorporates two types of layers stacked in an alternating fashion. The normal layers become superconducting due to the proximity to the planes below the critical temperature. We observe distinct behaviors for the penetration depth results along the two directions for a range of interlayer coupling strengths. We discuss the effects of the interlayer coupling strength and doping. Moreover, we compare our results with the experimental observations.

We study the penetration depths along the a(K a ), b(λb) and c(λ c )-axes in the presence of the pseudogap and d x2-y2 super-conducting phases (DSC) in a simple model for cuprates. The pseudogap phase is addressed within the framework of the ordered d-density wave (DDW). The above scenario is con-sidered using a mean-fleld calculation of the tight binding model which incorporates two layers - a CuO 2 plane and a CuO chain per unit cell. The CuO chains become superconducting due to the proximity to the planes below the critical temperature. Moreover our model includes a momentum dependent chain-plane coupling. We observe distinct behaviors for the penetration depth results along the three directions which is consistent with the anisotropy observed in the experimental results. The temperature dependence of λ c is exactly the same as that of the recent experimental results as actly the same as that of the recent experimental results as demonstrated for T c =18K in the underdoped region. We observe a qualititave difference in the temperature dependence of λ a and λ b when compared to our previous studies. How-ever the phase diagram due to inclusion of the momentum dependence of the coupling suffers no significant variation. The main result of our work then is that a simple proximity DDW model in which the pairing interaction is localized to the planes, and the planes are coupled to the chains through a momentum dependent term can account for many observed experimental properties. The inclusion of the pseudogap and also the value of the chain-plane coupling modifies the general trend of our results when compared to the simple DSC model without the coupling.

Cold hydrogen-hydrogen scattering has been investigated using close coupling approximation (CCA) model. The total wave function of the system is expanded in terms of atomic expansion basis. The effect of electron exchange and coupling to the continuum of both the atoms are taken into account. Singlet and triplet partial wave elastic and total cross-sections are presented and compared with existing theoretical predictions. Thermally averaged total cross-sections with respect to temperature are also provided along with their earlier results.

We study the effect of a magnetic field on the d-density wave (DDW) in the presence of d x 2 - y 2 superconducting order parameter (DSC) for high-temperature cuprates using a mean-field calculation of the tight binding model. The phase diagrams for the order parameter with doping are discussed. The phase diagram of the field with filling and also the dependence of the critical field ( H c ) on the critical temperature ( T c ) have been considered. The temperature dependence of the specific heat is also demonstrated. The effect of the field on the DDW order parameter and the superconducting gap are not alike. While the field suppresses the DSC gap, it tends to increase the DDW gap at the same doping. Moreover the gap to T c ratio increases with the field. The critical field has a power law dependence ( H c – T c 2 ).

We study the superconductivity in MgB2 using a tight binding model to investigate the doping dependence of the order parameter and the critical temperature. We consider both the anisotropic and the isotropic s-wave pairing to study the coexistence of the two gaps. A good agreement between the existing experiments and our theoretical curves is observed. The temperature dependence of order parameter, specific heat and penetration depth at half filling are also demonstrated and are found to be in accord with the available experimental predictions.

The low-energy (below 10-3 au) capture processes in hydrogen-anti-hydrogen scattering have been investigated using the plane wave approximation. The capture cross sections for the different excited states (up to the principal quantum number N = 24) of the protonium (Pn) atom, keeping the positronium (Ps) atom in its ground state, have been explicitly calculated. The present cross sections for the excited states of the Pn atom (N = 24, L = 0) are found to be in fair agreement with those of Jonsell et al (Jonsell S, Saenz A, Froelich P, Zygelman B and Dalgarno A 2001 Phys. Rev. A 64 052712). The s-state capture cross sections for the N = 17-23 excited states are found to be quite significant. The p-state cross sections are also not negligible.

We study the doping and temperature dependence of the order parameter for the triplet states of the layered perovskite material Sr2RuO4. The tight binding model that includes orthorhombic distortion and second nearest neighbor hopping, γ has been considered to study the doping and temperature dependence of the p- and f-wave states. We also calculate the temperature dependence of specific heat and thermal conductivity. We compare our results with the corresponding singlet \({\text{d}}_{x^2 - y^2 } \)-results of the cuprates. dxy-wave has also been considered. The jump in the specific heat at Tc (critical temperature) and its temperature dependence agree well with the experiment.