Estudo Geralhttps://estudogeral.sib.uc.ptThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 31 Jul 2021 22:54:54 GMT2021-07-31T22:54:54Z50121A plane-wave pseudopotential description of charged clustershttp://hdl.handle.net/10316/12346Title: A plane-wave pseudopotential description of charged clusters
Authors: Nogueira, Fernando; Martins, J. L.; Fiolhais, Carlos
Abstract: One of the most efficient approaches in computational cluster physics uses a plane-wave basis set and pseudopotentials to describe electron–ion interactions. This method – where the clusters are placed inside supercells – is restricted in its usual form to neutral systems because of the long-range interaction between a charged cluster and its periodic images. To eliminate this restriction, we propose to shield each charged cluster with a spherical shell having a symmetric charge that neutralizes the supercell. Furthermore, the shell is placed in such a way that it cancels the electric dipole of the charged cluster. We present relaxed geometries and cohesive energies of Na N +, N=2-9 and 21, obtained with Langevin quantum molecular dynamics. Our local density approximation structures are very similar to those found in other first principles calculations. Vertical and adiabatic ionization energies of Na N, N=2,?3,?6, and 8 are displayed. We also show results for Na 8 2+, Na 5 - and Na 7 -
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10316/123461999-01-01T00:00:00ZDescrição de propriedades físicas de sólidos e agregados com pseudopotenciaishttp://hdl.handle.net/10316/2173Title: Descrição de propriedades físicas de sólidos e agregados com pseudopotenciais
Authors: Nogueira, Fernando Manuel da Silva
Description: Tese de doutoramento em Física (Física Teórica) apresentada à Fac. de Ciências e Tecnologia da Univ. de Coimbra
Tue, 27 Jul 1999 00:00:00 GMThttp://hdl.handle.net/10316/21731999-07-27T00:00:00ZOxoperoxo Vanadium(V) Complexes of l-Lactic Acid: Density Functional Theory Study of Structure and NMR Chemical Shiftshttp://hdl.handle.net/10316/10379Title: Oxoperoxo Vanadium(V) Complexes of l-Lactic Acid: Density Functional Theory Study of Structure and NMR Chemical Shifts
Authors: Justino, Licínia L. G.; Ramos, M. Luísa; Nogueira, Fernando; Sobral, Abilio J. F. N.; Geraldes, Carlos F. G. C.; Kaupp, Martin; Burrows, Hugh D.; Fiolhais, C
Abstract: Various combinations of density functionals and pseudopotentials with associated valence basis-sets are compared for reproducing the known solid-state structure of [V2O2(OO)2l-lact2]2−cis. Gas-phase optimizations at the B3LYP/SBKJC level have been found to provide a structure that is close to that seen in the solid state by X-ray diffraction. Although this may result in part from error compensation, this optimized structure allowed satisfactory reproduction of solution multinuclear NMR chemical shifts of the complex in all-electron DFT-IGLO calculations (UDFT-IGLO-PW91 level), suggesting that it is probably close to that found in solution. This combination of approaches has subsequently been used to optimize the structures of the vanadium oxoperoxo complexes [V2O3(OO)l-lact2]2−cis, [V2O3(OO)l-lact2]2−trans, and [VO(OO)(l-lact)(H2O)]−cis. The 1H, 13C, 51V, and 17O NMR chemical shifts for these complexes have been calculated and compared with the experimental solution chemical shifts. Excellent agreement is seen with the 13C chemical shifts, while somewhat inferior agreement is found for 1H shifts. The 51V and 17O chemical shifts of the dioxo vanadium centers are well reproduced, with differences between theoretical and experimental shifts ranging from 22.9 to 35.6 ppm and from 25.1 to 43.7 ppm, respectively. Inferior agreement is found for oxoperoxo vanadium centers, with differences varying from 137.3 to 175.0 ppm for 51V shifts and from 148.7 to 167.0 ppm for 17O(oxo) shifts. The larger errors are likely to be due to overestimated peroxo O−O distances. The chosen methodology is able to predict and analyze a number of interesting structural features for vanadium(V) oxoperoxocomplexes of α-hydroxycarboxylic acids.
Mon, 18 Aug 2008 00:00:00 GMThttp://hdl.handle.net/10316/103792008-08-18T00:00:00ZCharged metal clusters : atomistic versus continuous background continuous descriptionshttp://hdl.handle.net/10316/41681Title: Charged metal clusters : atomistic versus continuous background continuous descriptions
Authors: Nogueira, Fernando; Vieira, Armando; Brajczewska, Marta; Fiolhais, Carlos
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10316/416811998-01-01T00:00:00ZHigh-throughput search of ternary chalcogenides for p-type transparent electrodeshttp://hdl.handle.net/10316/46711Title: High-throughput search of ternary chalcogenides for p-type transparent electrodes
Authors: Shi, J.; Cerqueira, T.F.T.; Cui, W.; Nogueira, F.; Botti, S.; Marques, M. A. L.
Tue, 07 Mar 2017 00:00:00 GMThttp://hdl.handle.net/10316/467112017-03-07T00:00:00ZEvanescent core pseudopotential: Applications to surfaces and clustershttp://hdl.handle.net/10316/12344Title: Evanescent core pseudopotential: Applications to surfaces and clusters
Authors: Fiolhais, Carlos; Nogueira, F.; Henriques, C.
Abstract: A new local pseudopotential, called the “evanescent core” pseudopotential, has recently been proposed for sp-bonded metals. It is fitted to dominant density parameters of the solid state (valence, average equilibrium valence electron density, and interstitial valence electron density), and it yields an overall good description of physical properties such as binding energies and bulk moduli, in the framework of second-order perturbation theory. The potential, therefore, takes into account the atomic structure of the metal beyond the stabilized jellium model or structureless pseudopotential model. We present applications of the pseudopotential to surfaces and clusters of Na, Mg and Al, specifically: (i) Band-structure effects on surface tension and work functions; (ii) Cohesive energies and optimized structures of small clusters with two and six atoms (the latter with octahedral symmetry). The results are compared with those of the stabilized jellium model
Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/10316/123441996-01-01T00:00:00ZTests of a density-based local pseudopotential for sixteen simple metalshttp://hdl.handle.net/10316/12363Title: Tests of a density-based local pseudopotential for sixteen simple metals
Authors: Pollack, L.; Perdew, John P.; He, Jingsong; Marques, M.; Nogueira, Fernando; Fiolhais, Carlos
Abstract: A comprehensive study of the lattice dynamics, elastic moduli, and liquid metal resistivities for 16 simple metals in the bcc and fcc crystal structures is made using a density-based local pseudopotential. The phonon frequencies exhibit excellent agreement with both experiment and nonlocal pseudopotential theory. The bulk modulus is evaluated by the long wave and homogeneous deformation methods, which agree after a correction is applied to the former. Calculated bulk and Voigt shear moduli are insensitive to crystal structure, and long-wavelength soft modes are found in certain cases. Resistivity calculations confirm that electrons scatter off the whole Kohn-Sham potential, including its exchange-correlation part as well as its Hartree part. All of these results are found in second-order pseudopotential perturbation theory. However, the effect of a nonperturbative treatment on the calculated lattice constant is not negligible, showing that higher-order contributions have been subsumed into the pseudopotential by construction. For bcc sodium, the band structures of local and nonlocal pseudopotentials are found to be almost identical
Wed, 01 Jan 1997 00:00:00 GMThttp://hdl.handle.net/10316/123631997-01-01T00:00:00ZTrends in the properties and structures of the simple metals from a universal local pseudopotentialhttp://hdl.handle.net/10316/12360Title: Trends in the properties and structures of the simple metals from a universal local pseudopotential
Authors: Nogueira, Fernando; Fiolhais, Carlos; Perdew, John P.
Abstract: The properties of simple metals are fixed primarily by the equilibrium average valence-electron density parameter rs, and secondarily by the valence z. The simplest level of theory that can account quantitatively for these trends invokes a “universal” local electron-ion pseudopotential, defined for each pair (rs,z) and treated as a second-order perturbation. We construct this pseudopotential from two conditions: (1) The total energy should minimize at the equilibrium Wigner-Seitz radius z1/3rs. (2) The bulk modulus should equal the realistic rs-dependent prediction of the stabilized jellium model with effective valence z*=1. These conditions can be satisfied by an analytic local pseudopotential depending upon two parameters other than z; we show that the choice of the two-parameter form (evanescent core vs Heine-Abarenkov) is not important. Our universal local pseudopotential is applied to calculate realistic bulk binding energies, pressure derivatives of bulk moduli, Voigt shear moduli, and interstitial electron numbers, revealing their trends as functions of rs and z. Equilibrium crystal structures are mapped in the rs-z plane, where the Hume-Rothery rules for substitutional alloys are manifest. The effect of pressure on crystal structure is also examined
Fri, 15 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10316/123601999-01-15T00:00:00ZTransferability of a local pseudopotential based on solid-state electron densityhttp://hdl.handle.net/10316/12358Title: Transferability of a local pseudopotential based on solid-state electron density
Authors: Nogueira, Fernando; Fiolhais, Carlos; He, Jingsong; Perdew, John P.; Rubio, Angel
Abstract: Local electron - ion pseudopotentials fitted to dominant density parameters of the solid state (valence, equilibrium average electron density and interstitial electron density) have been constructed and tested for sixteen simple metals. Calculated solid-state properties present little evidence of the need for pseudopotential non-locality, but this need is increasingly evident as the pseudopotentials are transferred further from their solid-state origins. Transferability is high for Na, useful for ten other simple metals (K, Rb, Cs, Mg, Al, Ga, In, Tl, Sn, and Pb), and poor for Li, Be, Ca, Sr and Ba. In the bulk solid, we define a predictor of transferability and check the convergence of second-order pseudopotential perturbation theory for bcc Na. For six-atom octahedral clusters, we find that the pseudopotential correctly predicts self-compressions or self-expansions of bond length with respect to the bulk for Li, Na, Mg, and Al, in comparison with all-electron results; dimers of these elements are also considered. For the free atom, we examine the bulk cohesive energy (which straddles the atomic and solid-state limits), the atomic excitation energies and the atomic density. For the cohesive energy, we also present the results of the simpler stabilized jellium and universal-binding-energy-curve models. The needed non-locality or angular-momentum dependence of the pseudopotential has the conventional character, and is most strongly evident in the excitation energies
Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/10316/123581996-01-01T00:00:00ZStructure Dependence of Hyperpolarizability in Octopolar Moleculeshttp://hdl.handle.net/10316/10521Title: Structure Dependence of Hyperpolarizability in Octopolar Molecules
Authors: Cardoso, C.; Abreu, P. E.; Nogueira, F.
Abstract: Recent Hyper Rayleigh Scattering measurements report a significant increase of second-order hyperpolarizability upon introduction of positive charges at the pyridyl end groups in trispyridyl octopolar chromophores. We calculated the geometries, linear response, and first-order hyperpolarizabilities of a series of six trispyridyl molecules both in the neutral and protonated forms. The calculations were performed with ab initio and semiempirical methods. The results are in good agreement with the experimental values and a correlation between the first hyperpolarizability and two structural properties, the N−C bond elongation and the C−C bond length alternation, Δr was established. To test these effects we computed the hyperpolarizability for several constrained geometries and confirmed the importance of planarity on the hyperpolarizability values. However the Δr values alone seem to have little influence both on the hyperpolarizability and on the gap values. Replacing the triple C≡C bond by a double C=C bond in the conjugation bridge has no significant effect due to the strong hyperpolarizability dependence on the pyridyl-benzene dihedral angle.
Tue, 14 Apr 2009 00:00:00 GMThttp://hdl.handle.net/10316/105212009-04-14T00:00:00ZGenerating relativistic pseudo-potentials with explicit incorporation of semi-core states using APE, the Atomic Pseudo-potentials Enginehttp://hdl.handle.net/10316/4335Title: Generating relativistic pseudo-potentials with explicit incorporation of semi-core states using APE, the Atomic Pseudo-potentials Engine
Authors: Oliveira, Micael J. T.; Nogueira, Fernando
Abstract: We present a computer package designed to generate and test norm-conserving pseudo-potentials within Density Functional Theory. The generated pseudo-potentials can be either non-relativistic, scalar relativistic or fully relativistic and can explicitly include semi-core states. A wide range of exchange-correlation functionals is included.Program summary
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10316/43352008-01-01T00:00:00ZStructural phase transitions in Na, Mg and Al crystals: dominant role of the valence in local pseudopotential theoryhttp://hdl.handle.net/10316/4533Title: Structural phase transitions in Na, Mg and Al crystals: dominant role of the valence in local pseudopotential theory
Authors: Perdew, John P.; Nogueira, Fernando; Fiolhais, Carlos
Abstract: Within a perturbative treatment of realistic local electron-ion pseudopotentials for the simple metals, we study structural phase transitions under pressure in Na and other monovalent metals, Mg and other divalent metals, and Al and other trivalent metals. For the "good local pseudopotential" metals Na, Mg, and Al, our results are in reasonable agreement with experiment. The sequence of predicted transitions between crystal structures, and the volume compression ratios V/V0 at which these transitions are predicted, are determined largely by the valence z. The valence z also determines the dependence of the total energy upon the tetragonal c/a ratio along the Bain path from bcc to fcc. This path shows the divalent metals unstable in both fcc and bcc structures, and the trivalent metals unstable in bcc.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10316/45332000-01-01T00:00:00Z