Supercell Calculations Research Articles

DIRAC-CONE PHOTONIC SURFACE STATES IN THREE-DIMENSIONAL PHOTONIC CRYSTAL SLAB

We present a multiple-scattering method in conjunction with supercell calculations to study the electromagnetic surface states in three-dimensional photonic crystal (PC) slab. Using our technique, we obtain the first prediction of Dirac-cone photonic surface state in some three-dimensional PC slabs. Such a state can be used to investigate some extremal transmission phenomena of electromagnetic waves near the Dirac point on the surface of the crystal, which is similar to the case of electron on the surface of topological insulators.

Topological phase transitions in (Bi1−xInx)2Se3and (Bi1−xSbx)2Se3

We study the phase transition from a topological to a normal insulator with concentration $x$ in (Bi${}_{1\ensuremath{-}x}$In${}_{x}{)}_{2}$Se${}_{3}$ and (Bi${}_{1\ensuremath{-}x}$Sb${}_{x}{)}_{2}$Se${}_{3}$ in the Bi${}_{2}$Se${}_{3}$ crystal structure. We carry out first-principles calculations on small supercells, using this information to build Wannierized effective Hamiltonians for a more realistic treatment of disorder. Despite the fact that the spin-orbit coupling (SOC) strength is similar in In and Sb, we find that the critical concentration ${x}_{\mathrm{c}}$ is much smaller in (Bi${}_{1\ensuremath{-}x}$In${}_{x}{)}_{2}$Se${}_{3}$ than in (Bi${}_{1\ensuremath{-}x}$Sb${}_{x}{)}_{2}$Se${}_{3}$. For example, the direct supercell calculations suggest that ${x}_{\mathrm{c}}$ is below $12.5%$ and above 87.5$%$ for the two alloys, respectively. More accurate results are obtained from realistic disordered calculations, where the topological properties of the disordered systems are understood from a statistical point of view. Based on these calculations, ${x}_{c}$ is around $17%$ for (Bi${}_{1\ensuremath{-}x}$In${}_{x}{)}_{2}$Se${}_{3}$, but as high as 78%--83% for (Bi${}_{1\ensuremath{-}x}$Sb${}_{x}{)}_{2}$Se${}_{3}$. In (Bi${}_{1\ensuremath{-}x}$Sb${}_{x}{)}_{2}$Se${}_{3}$, we find that the phase transition is dominated by the decrease of SOC, with a crossover or ``critical plateau'' observed from around 78$%$ to 83$%$. On the other hand, for (Bi${}_{1\ensuremath{-}x}$In${}_{x}{)}_{2}$Se${}_{3}$, the In 5$s$ orbitals suppress the topological band inversion at low-impurity concentration, therefore accelerating the phase transition. In (Bi${}_{1\ensuremath{-}x}$In${}_{x}{)}_{2}$Se${}_{3}$ we also find a tendency of In atoms to segregate.

Theory of local electric polarization and its relation to internal strain: Impact on polarization potential and electronic properties of group-III nitrides

We present a theory of local electric polarization in crystalline solids and apply it to study the case of wurtzite group-III nitrides. We show that a local value of the electric polarization, evaluated at the atomic sites, can be cast in terms of a summation over nearest-neighbor distances and Born effective charges. Within this model, the local polarization shows a direct relation to internal strain and can be expressed in terms of internal strain parameters. The predictions of the present theory show excellent agreement with a formal Berry phase calculation for random distortions of a test-case CuPt-like InGaN alloy and InGaN supercells with randomly placed cations. While the present level of theory is appropriate for highly ionic compounds, we show that a more complex model is needed for less ionic materials, in which the strain dependence of Born effective charges has to be taken into account. Moreover, we provide ab initio parameters for GaN, InN and AlN, including hybrid functional values for the piezoelectric coefficients and the spontaneous polarization, which we use to accurately implement the local theory expressions. In order to calculate the local polarization potential, we also present a point dipole method. This method overcomes several limitations related to discretization and resolution which arise when obtaining the local potential by solving Poisson's equation on an atomic grid. Finally, we perform tight-binding supercell calculations to assess the impact of the local polarization potential arising from alloy fluctuations on the electronic properties of InGaN alloys. In particular, we find that the large upward bowing with composition of the InGaN valence band edge is strongly influenced by local polarization effects. Furthermore, our analysis allows us to extract composition-dependent bowing parameters for the energy gap and valence and conduction band edges.

Trapping of interstitial defects: filling the gap between the experimental measurements and DFT calculations

We show that any impurity will slow the diffusion of oxygen in Nb. Using a first-principles plane-wave pseudopotential method and the supercell model, we calculated the interaction energies between substitutional atoms (SA) (X = Ti, V, Ta, Zr, and Hf) and interstitial oxygen in a Nb matrix. All impurities act as traps for oxygen: undersized SA (Ti and V) have strongest binding at the nearest octahedral interstice, while for oversized SA (Zr and Hf), the strongest trapping site is the second-nearest octahedral interstice. We evaluated the diffusion coefficients of O in the Nb–X alloys using kinetic Monte Carlo (KMC) modeling based in the transition state theory, using our calculated oxygen migration energies. From this, the effective (average) X–O interaction energies were extracted using the Oriani model (Oriani 1970 Acta Metall. 18 147–57). The effective X–O interaction energies are close to the strongest interaction energies between X and O obtained from the direct supercell calculations. The phenomenological effective diffusion barrier obtained from the KMC modeling is close to the energy difference between the most stable configuration and the highest saddle point along the diffusion path. Both results demonstrate that the weaker trapping site has negligible influence on the diffusion of O.

Intrinsic Properties of Fe-Substituted $L1_{0}$ Magnets

First-principle supercell calculations are used to determine how 3d elemental additions, especially Fe additions, modify the magnetization, exchange and anisotropy of L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -ordered ferromagnets. Calculations are performed using the VASP code and partially involve configurational averaging over site disorder. Three isostructural systems are investigated: Fe-Co-Pt, Mn-Al-Fe, and transition metal-doped Fe-Ni. In all three systems the iron strongly influences the magnetic properties of these compounds, but the specific effect depends on the host. In CoPt(Fe) iron enhances the magnetization, with subtle changes in the magnetic moments that depend on the distribution of the Fe and Co atoms. The addition of Fe to MnAl is detrimental to the magnetization, because it creates antiferromagnetic exchange interactions, but it enhances the magnetic anisotropy. The replacement of 50% of Mn by Fe in MnFeAl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> enhances the anisotropy from 1.77 to 2.5 MJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Further, the substitution of light 3d elements such as Ti, V, Cr into L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -ordered FeNi is shown to substantially reduce the magnetization.

Implementation of non-equilibrium vertex corrections in KKR: transport through disordered layers

The theoretical description of modern nanoelectronic devices requires a quantum mechanical treatment and often involves disorder, e.g. from alloys. Therefore, the ab initio theory of transport using non-equilibrium Green’s functions is extended to the case of disorder described by the coherent potential approximation. This requires the calculation of non-equilibrium vertex corrections. We implement the vertex corrections in a Korringa–Kohn–Rostoker multiple scattering scheme. In order to verify our implementation and to demonstrate the accuracy and applicability we investigate a system of an iron-cobalt alloy layer embedded in copper. The results obtained with the coherent potential approximation are compared to supercell calculations. It turns out that vertex corrections play an important role for this system.

Application of attractive potential by DFT + U to predict the electronic properties of materials without highly localized bands

It is well known that density functional theory (DFT) underestimates band gaps of materials which have highly localized valence electrons. On the other hand, the predictions of electronic properties of materials, which do not have localized band near the band gap, by DFT are not accurate enough as well. The effect of electronic correlation on properties of this second group of materials such as, in particular, gallium phosphide (GaP) is theoretically studied in this paper. The goal is to find and physically justify a computationally economical but reasonably accurate method to study such materials. The electronic correlation in GaP has been varied by using DFT based methods, such as in DFT+U, with different U-values for gallium d and phosphorus p orbitals. The fact that GaP does not have partially filled localized orbitals, such as 3d orbitals in ZnO, the justification for the use of DFT+U is rather challenging. DFT+U method, as is applied here in an unconventional way to include attractive potentials, correct the shortcoming of DFT in a very economical way by improving both the band gap and mechanical properties. These results will facilitate large supercell calculations for doping or alloying in GaP or similar materials.

Thermal Decomposition Mechanisms of Nitroesters: Ab Initio Modeling of Pentaerythritol Tetranitrate

The lack of fundamental understanding of the intricate interplay between large amounts of chemical energy stored in energetic molecular materials and their sensitivity to detonation initiation represents a stubborn outstanding challenge. This study sheds much needed light on the atomic decomposition mechanisms of nitroesters with an example of pentaerythritol tetranitrate (C5H8N4O12, also known as PETN), used as an explosive and a medication. The performed study is based on density functional theory combined with variational transition-state theory and large-scale massively parallel periodic supercell calculations and presents a detailed analysis of thermal initiation of chemical reactions and their kinetics in the gas-phase PETN molecules, the ideal bulk crystals, and on two low energy surfaces, (101) and (110). The obtained activation barriers, reaction energies, and reaction rates of simulated bond dissociation mechanisms reveal that the overall decomposition of condensed nitroesters is defined by the ...

Piezoelectricity in PbZrxTi1-xO3 Studied by Density-Functional Perturbation Theory Supercell Calculations

First-principles calculations of the piezoresponses (e33) of PbZrxTi1-xO3 (PZT) with various crystalline phases and Zr/Ti ratios (composition: B-site cations) are performed at room temperature using density-functional perturbation theory (DFPT) to understand the experimental observation that large piezoresponses occur at the morphotropic phase boundary (MPB). The results of ab initio calculations indicate that PZT (Zr/Ti = 52/48) with a tetragonal (P4MM) phase shows the lowest formation energy (stable) and the highest piezoelectric coefficient, e33, in the MPB region. The Z*/Δε ratio (where Z* is the Born effective charge and Δε is the variation in the internal strain) is computed, and we find that laterally bonded oxygen atoms are the main contributors to e33 in the above structure owing to the low Δε3 caused by perturbation.

Modeling of crystal field and spin-Hamiltonian parameters for Ti3+:MgO

The aim of this paper is to model the crystal field parameters (CFPs) and spin-Hamiltonian parameters (g factors g||, g⊥ and hyperfine structure constants A||, A⊥) for the Ti3+:MgO system. The CFPs were modeled in the frame of superposition model of the crystal field theory, based on ab initio supercell calculations of Ti3+:MgO geometry and crystal field parameter 10Dq. The obtained values were used to simulate the energy levels scheme, by diagonalizing the full energy matrix of the Hamiltonian. The EPR parameters have been calculated from both the complete diagonalization method and the perturbation theory method. All the obtained results (optical and EPR) were compared with experimental data and a good agreement is observed.

Ab initio study on the size effect of symmetric and asymmetric ferroelectric tunnel junctions: A comprehensive picture with regard to the details of electrode/ferroelectric interfaces

Ferroelectric size effect of BaTiO3 (BTO) tunnel junctions with metal Pt and/or oxide SrRuO3 (SRO) electrodes has been comprehensively investigated by the first-principle calculations. A vacuum layer is included in the supercell calculations, so that full-relaxation is achieved without artificial constraint on the supercell strains. We have constructed all of ten possible types of tunnel junctions with either symmetric or asymmetric geometries to systematically explore the influence of electrode/ferroelectric interfaces. The characteristics of atomic structure, polarization, charge density, and electrostatic potential for different geometries and sizes are revealed. It is found that the ferroelectric stability of a tunnel junction depends significantly on the details of the two electrode/ferroelectric interfaces, which present specific short- and long-range properties, e.g., local bonding environment, electronic screening, built-in field, etc. Result shows that Pt/BTO interfaces have strong coupling with ferroelectric distortion and thus play more dominant roles than the SRO/BTO interfaces in affecting the ferroelectric stability of the tunnel junctions. Particularly, it is found that Pt2/TiO2 interface can induce collective ferroelectric distortion in the initially non-distorted barrier. With a full-relaxation of the strains, an abnormal enhancement of ferroelectricity by Pt2/BaO interface due to Pt-O bonding effect is demonstrated, where a strong interfacial-bonding-related polarizing field is verified. Also importantly, polarization stability of asymmetric tunnel junctions is found dependent on direction, manifested with the appearing of a new critical thickness, below which the tunnel junction loses polarization bistability. Furthermore, it shows that the local features of a specific electrode/ferroelectric interface (e.g., the interfacial atomic structure, local polarization, charge transfer, and potential step) are well kept in different types of tunnel junctions. By analyzing and summarizing the results, our results suggest that traditional phenomenological models need several modifications in order to quantitatively reproduce the size effect of ferroelectric tunnel junctions. Our study provides a comprehensive picture of the ferroelectric size effect in BTO tunnel junctions as a function of electrode/ferroelectric interfaces and should have valuable implications for future studies and applications.

The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment

We have carried out a theoretical and experimental investigation of the beryllium K-edge soft x-ray absorption fine structure of beryllium compounds in the oxygen group, considering BeO, BeS, BeSe, and BeTe. Theoretical spectra are obtained ab initio, through many-body perturbation theory, by solving the Bethe–Salpeter equation (BSE), and by supercell calculations using the core-hole approximation. All calculations are performed with the full-potential linearized augmented plane-wave method. It is found that the two different theoretical approaches produce a similar fine structure, in good agreement with the experimental data. Using the BSE results, we interpret the spectra, distinguishing between bound core-excitons and higher energy excitations.

Behavior of Transuranic Mixed-Oxide Fuel in a CANDU-900 Reactor

The production of transuranic actinide fuels for use in current thermal reactors provides a useful intermediary step in closing the nuclear fuel cycle. Extraction of actinides reduces the longevity, radiation, and heat loads of spent material. The burning of transuranic (TRU) fuels in current reactors for a limited amount of cycles reduces the infrastructure demand for fast reactors and provides an effective synergy that can result in a reduction of as much as 95% of spent fuel waste while significantly reducing the fast reactor infrastructure needed. This paper examines the features of actinide mixed-oxide (MOX) fuel, TRUMOX, in a CANDU® nuclear reactor. The actinide concentrations used were based on extraction from 30-year-cooled spent fuel and mixed with natural uranium in 3.1 wt% actinide MOX fuel. Full lattice cell modeling was performed using the WIMS-AECL code, supercell calculations were analyzed in DRAGON, and full-core analysis was executed in the RFSP two-group diffusion code. A time-average full-core model was produced and analyzed for reactor coefficients, reactivity device worth, and online fueling impacts. The standard CANDU operational limits were maintained throughout operations. The TRUMOX fuel design achieved a burnup of 29.91 MWd/kg heavy element and an actinide transmutation rate of 35% for a single pass. A fully TRUMOX-fueled CANDU was shown to operate within acceptable limits and provided a viable intermediary step for burning actinides. The recycling, reprocessing, and reuse of spent fuels produces a much more sustainable and efficient nuclear fuel cycle.

First-principles study of fcc-Ag/bcc-Fe interfaces

Ab initio calculations are employed to determine the lower and upper bounds of the interfacial energy and work of separation of a fcc-Ag/bcc-Fe interface. The strain-free interfacial energy of the coherent interface is taken as the lower bound and the interfacial energy of the commensurate incoherent interface as the upper bound of the interfacial energy of a realistic semicoherent interface. The latter is estimated by applying an averaging scheme based on the interfacial energies obtained for the coherent interfaces. Similar calculations are performed for determining the bounds of the work of separation. We justify the use of the averaging scheme by carrying out large supercell calculations for a semicoherent interface. For a Fe(110)/Ag(111) semicoherent interface, we show that taking either Fe or Ag as the underlying lattice, our averaging scheme can yield a reasonable estimation of the work of separation of the semicoherent interface. However, when taking Ag as the underlying lattice, the averaged interfacial energy of the semicoherent interface is significantly underestimated due to the magnetism. The structure and magnetism at the coherent and semicoherent interfaces are discussed.

Cu2+ in Layered Compounds: Origin of the Compressed Geometry in the Model System K2ZnF4:Cu2+

Many relevant properties (including superconductivity and colossal magnetoresistance) of layered materials containing Cu(2+), Ag(2+), or Mn(3+) ions are commonly related to the Jahn-Teller instability. Along this line, the properties of the CuF6(4-) complex in the K2ZnF4 layered perovskite have recently been analyzed using a parametrized Jahn-Teller model with an imposed strain [Reinen, D. Inorg. Chem.2012, 51, 4458]. Here, we present results of ab initio periodic supercell and cluster calculations on K2ZnF4:Cu(2+), showing unequivocally that the actual origin of the unusual compressed geometry of the CuF6(4-) complex along the crystal c axis in that tetragonal lattice is due to the presence of an electric field due to the crystal surrounding the impurity. Our calculations closely reproduce the experimental optical spectrum. The calculated values of the equilibrium equatorial and axial Cu(2+)-F(-) distances are, respectively, R(ax) = 193 pm and R(eq) = 204 pm, and so the calculated distortion R(ax) - R(eq) = 11 pm is three times smaller than the estimated through the parametrized Jahn-Teller model. As a salient feature, we find that if the CuF6(4-) complex would assume a perfect octahedral geometry (R(ax) = R(eq) = 203 pm) the antibonding a(1g)*(∼3z(2) - r(2)) orbital is placed above b(1g)*(∼x(2) - y(2)) with a transition energy E((2)A(1g) → (2)B(1g)) = 0.34 eV. This surprising fact stresses that about half the experimental value E((2)A(1g) → (2)B(1g)) = 0.70 eV is not due to the small shortening of the axial Cu(2+)-F(-) distance, but it comes from the electric field, E(R)(r), created by the rest of the lattice ions on the CuF6(4-) complex. This internal field, displaying tetragonal symmetry, is thus responsible for the compressed geometry in K2ZnF4:Cu(2+) and the lack of symmetry breaking behind the ligand relaxation. Moreover, we show that the electronic energy gain in this process comes from bonding orbitals and not from antibonding ones. The present results underline the key role played by ab initio calculations for unveiling all the complexity behind the properties of the model system K2ZnF4:Cu(2+), opening at the same time a window for improving our knowledge on d(9), d(7), or d(4) ions in other layered compounds.

Paramagnetic Defects in Polycrystalline Zirconia: An EPR and DFT Study

The paramagnetic defects present in pristine zirconium dioxide (ZrO2) and those formed upon reductive treatments (either annealing or UV irradiation in H2) are described and rationalized by the joint use of electron paramagnetic resonance (EPR) and DFT supercell calculations. Three types of Zr3+ reduced sites have been examined both in the bulk of the solid (one center) and at the surface (two centers). Trapping electron centers different from reduced Zr ions are also present, whose concentration increases upon annealing. A fraction of these sites are paramagnetic showing a symmetric signal at g = 2.0023, but the majority of them are EPR silent and are revealed by analysis of electron transfer from the reduced solid to oxygen. The presence of classic F-type centers (electrons in bulk oxygen vacancies) is disregarded on the basis of the g-tensor symmetry. This is expected, on the basis of theoretical calculations, to be anisotropic and thus incompatible with the observed signal. In general terms, ZrO2 has ...

The substitution effects on electronic structure of iron selenide superconductors

The influence of a partial substitution with S, Te, Co, Ni and Cu atoms on the electronic structure of the FeSe superconductor has been investigated within the density functional theory. The results of the supercell calculations reveal distinct changes of electronic structures of the substituted FeSe systems, which can be responsible for their superconducting properties. The replacement of Se atoms by Te or S ones yields imperfect nesting between the holelike and electronlike Fermi surface (FS) sheets, which enhances magnetic fluctuations responsible for superconducting pairing, thus leading to higher values of the superconducting critical temperatures. Meanwhile, the substitutions with transition-metal atoms for iron sites make more substantial changes of the FSs topology, since the holelike cylinders shrink at the cost of an enlargement of the electronlike ones. Thus, the superconducting pairing, driven by the nesting between these sheets, weakens and superconductivity disappears for a small percentage of dopants. The results support the idea of spin-fluctuation mediated superconductivity in iron chalcogenides.

Colour due to Cr3+ ions in oxides: a study of the model system MgO:Cr3+

Seeking to understand why the cubic centre in MgO:Cr3+ has the same 10Dq value as emerald, ab initio cluster and periodic supercell calculations have been performed. It is found that the equilibrium Cr3+–O2− distance, R, in MgO:Cr3+ is equal to 2.03 Å and thus 0.06 Å higher than that measured for the emerald. Calculations carried out on the isolated complex at R = 2.03 Å give 10Dq = 14 510 cm−1, which is 10% smaller than the experimental figure for MgO:Cr3+. Nevertheless, when the internal electric field, ER(r), due to the rest of the lattice ions is also taken into account, the calculated 10Dq = 16 210 cm−1 coincides with the experimental value. Accordingly, the colour shift for different oxides doped with Cr3+ can be well understood on the basis of this extrinsic contribution to 10Dq usually ignored in a ligand field description. The calculated electrostatic potential, VR(r), related to ER(r), is found to be attractive when the electronic density is lying along 〈110〉 directions and |r| > 1 Å driven by the first shell of twelve Mg2+ ions. The action of VR(r) upon the complex slightly decreases the energy of t2g(xy,xz,yz) orbitals with respect to that for eg(3z2 − r2,x2 − y2) orbitals, thus enhancing the 10Dq value by 0.2 eV. However, the addition of VR(r) induces very small changes in the electronic density, a relevant fact that is related to the emission energy being nearly independent of the host lattice along the series of Cr3+-doped oxides.

Ab initio energetics of charge compensating point defects: A case study on MgO

Density functional theory (DFT) calculations using supercells have proven quite successful in predicting defect properties. Although forming defect groups, for example, the Schottky pair VO••+VMg″ in MgO, are usually energetically favorable in many ionic systems, it is useful to obtain the defect energies of such systems without any defect-defect interactions as reference energies. However, determining non-interacting energies through multi-defect supercell calculations is challenging due to interactions between the defects that are difficult to quantify and can only be avoided by using very large supercells. One solution to this problem is to build an effective multi-defect cell through separate isolated defect calculations, with each defect in their own supercell. However, this isolated defect approach requires that the charge compensation be introduced through charged supercells, and a careful treatment of the cell energetics and electron reference energy is required. In this paper we assess the use of an isolated defect approach for modeling charge-compensating defect groups using the test case of MgO. The appropriate asymptotic condition for the electron reference energy shift is formulated and a method to meet the condition is given. We also demonstrate the strong coupling effect between residual strain energy and electrostatic energy in charged cells, demonstrating that these two effects cannot generally be separated and treated in isolation. The key steps in an approach that yields accurate defect group energies from the isolated defect calculations are presented. The non-interacting Schottky defect formation energy in MgO is determined to be 6.1eV through calculation of separated isolated charged cells containing VO•• and VMg″, respectively, while the binding energy between the charged defects VO•• and VMg″ is determined to be 1.5eV. This approach may also be of value for accurate modeling of general isolated defects. The formation energy of an isolated neutral Mg vacancy is found to be lower than that of a Schottky pair, suggesting that it is possible to have significant thermal cation defect formation in MgO without forming charge compensating Schottky pairs.

Fermi surface reconstruction of superoxygenated La2CuO4superconductors with ordered oxygen interstitials

Novel imaging methods show that the mobile dopants in optimum doped La$_2$CuO$_{4+y}$ (LCO) get self-organized, instead of randomly distributed. Rigid-band models fail because of ordering of dopants and supercell calculations are required to obtain the Fermi surface reconstruction. We have performed advanced band calculations for a large supercell La$_{16}$Cu$_8$O$_{32+N}$ where $N$=1 or 2 oxygen interstitials form rows in the spacer La$_{16}$O$_{16+N}$ layers intercalated between the CuO$_2$ layers as determined by scanning nano x-ray diffraction. The additional oc cupied states made by interstitial oxygen orbitals sit well below the Fermi level ($E_F$) and lead to hole doping as expect ed. The unexpected results show that in the heavily doped puddles the altered Cu(3d)-O(2p) band hybridization at $E_F$ indu ces a multiband electronic structure with the formation of multiple Fermi surface spots: a) small gaps appear in the folde d Fermi surface, b) three mini-bands cross $E_F$ with reduced Fermi energies of 60, 150, and 240 meV respectively, c) the d ensity-of-states and band mass at $E_F$ show substantial increases, and d) spin-polarized calculations show a moderate incr ease of antiferromagnetic spin fluctuations. All calculated features are favorable to enhance superconductivity however the comparison with experimental methods probing the average electronic structure of cuprates will require the description of the electronics of a network of multigap superconducting puddles.