Spin-resolved Density Of States Research Articles

Interface defect state induced spin injection in organic magnetic tunnel junctions

This article analytically explores defect assisted spin injection in organic magnetic tunnel junctions (MTJs) [x/rubrene/Co, x = La2O3, LaMnO3, La0.7Ca0.3MnO3 (LCMO), La0.7Sr0.3MnO3 (LSMO)] employing nonequilibrium Green’s function (NEGF). Spin precession at ferromagnet (FM)/organic semiconductor (OSC) interface defect states have been considered while modeling the MTJ devices. Variations in voltage dependent parallel (RP) and antiparallel (RAP) resistances have been attributed to modified spin dependent scattering at modified spin resolved density of states of magnetic electrodes. Moreover, change in distribution of defect state depths at a spin injection interface has also been observed to modify RP/RAP, and hence, tunnel magnetoresistance (TMR) across the devices. Localization of defect state distribution due to a high spin split band may have resulted in large TMR for La2O3 devices. Nonlinear spin transfer torque (STT) in devices other than LSMO indicates compensation of spin damping, resulting in a high TMR response across the devices. Hence, the localization of defect state distribution and the choice of magnetic electrodes with high spin split bands may be exercised to realize spintronic devices for low power spin memory applications.

Computational exploration of Cs2LiMoX6 (X=Cl, I) halide double perovskites: Unveiling energy storage potentials

Density functional theory (DFT) simulations were conducted to investigate the physical characteristics of materials Cs2LiMoCl6 and Cs2LiMoI6. The magnetic and electronic features were examined using the Perdew, Burke, and Ernzerhof generalized-gradient approximation (PBE-GGA). Confirmation of the semiconductor behavior was attained through the spin-resolved density of states (DOS) and band structure (BS) plots. In this investigation, the computed band gap (Eg) values for Cs2LiMoI6 are identified as 0.96 eV in the spin-down channel and 1.76 eV in the spin-up channel. Likewise, for Cs2LiMoCl6, the Eg is determined to be 3.35 eV in the spin-down channel and 1.63 eV in the spin-up channel. From magnetic characteristics, the magnetic moments (μB) of 3.02436 μB and 3.00332 μB are calculated for Cs2LiMoCl6 and Cs2LiMoI6, respectively. The ferromagnetic (FM) nature is observed from the integral values of the magnetic moment. The Mo-4d-t2g orbitals play a pivotal role in determining the magnetic properties observed in perovskite materials. The study also explored optical properties, and the values of ε1(ω) at zero energy are approximately 4.84 and 3.20 for Cs2LiMoI6 and Cs2LiMoCl6, respectively. The maximum values of σ(ω) are observed to be 4631 (Ω cm)−1 and 3618 (Ω cm)−1 at 6.24 eV and 8 eV for Cs2LiMoI6 and Cs2LiMoCl6, respectively, signifying their suitability to the UV light region. Overall, these findings suggest the suitability of both materials for photovoltaics and other related applications.

Bound states and controllable currents on topological insulator surfaces with extended magnetic defects

We show that a magnetic line defect on the surface of a topological insulator generically supports two distinct branches of spin-polarized and current-carrying one-dimensional bound states. We identify the components of magnetic scattering that lead to the bound states. The velocity, and hence spin texture, of each of those branches can be independently tuned by a magnetic field rotated in the plane of the surface. We compute the local net and spin-resolved density of states as well as spin accumulation and charge currents. The net spin polarization and current due to both bound and scattering states vary stepwise as a function of the electrostatic and magnetic components of the scattering potential, and can be tuned by an applied field. We discuss stability of the bound states with respect to impurity scattering.

Carbon-induced magnetic properties and anomalous Hall effect in Co2Mn2C thin films with L10 -like structures

${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$ thin films were synthesized via vacuum carburization of the host CoMn alloy films based on a conventional gas-solid reaction to demonstrate the effect of C, a common light element, on the magnetic and spintronic materials. The crystal structure transitioned from the disordered face-centered-cubic CoMn to the $L{1}_{0}$-like ${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$, for which the lattice constant increased from 0.356 to 0.378 nm. The C $1s$ x-ray photoemission spectra of the ${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$ film indicated hybridization in C-Co and C-Mn and a homogeneous concentration of C in the film. The enhancement of both the saturation magnetization and the anomalous Hall conductivity (${\ensuremath{\sigma}}_{xy}$) was induced by C, attributing to the magnetic transition to the ferrimagnetic spin order. The surface flatness and high ${\ensuremath{\sigma}}_{xy}$ are promising characteristics for spintronic applications such as the spin-anomalous Hall effect. The atom- and spin-resolved density of states (DOS) via first-principles calculations revealed that face-centered Mn(II) and Co could be significantly influenced by C because of p-d hybridization, resulting in enhanced spin polarization of the DOS at the Fermi level of \ensuremath{\sim}0.82. These results demonstrate that the use of C could be an essential way to boost material properties in the future.

Half-metallic behavior Co2YAl (Y= Mo,Tc) compounds

The present manuscript reports structural stability, half-metallic behavior, thermophysical and thermoelectric properties of Co2MoAl and Co2TcAl full Heusler compounds using first-principle calculations. The full-potential linearized augmented plane wave method within the framework of density functional theory is implemented and WIEN2k code is incorporated in the stable Fm- 3m phase to attain the desired results. The L21 phase is found as the most stable phase for both compounds. The optimized equilibrium lattice parameters in the stable phase are 5.89Å, 5.86Å for Co2MoAl and Co2TcAl respectively. The electronic band structure study proves that both compounds Co2MoAl and Co2TcAl have indirect band gaps of 0.74eV and 0.85eV respectively in majority spin alignment. The half-metallic performance of the present set of compounds is explained by the spin-resolved density of states. The Fermi level at the Brillouin zone point approves the metallic as well as semiconducting behavior. To elucidate the thermodynamical stability of these materials against pressure and temperature by implementing the quasi-harmonic approximation of various parameters like Debye temperature, Gruneisen parameters and specific heat are studied successfully. To know the thermoelectric response, Seebeck coefficient and electrical conductivity are computed using the BoltzTrap code. The thermodynamic profile delivers that the present set of compounds possesses no anomalies with respect to the phase transition or instabilities. The computational study insights that the compounds can be synthesized experimentally and find a route towards spintronic and thermoelectric applicability.

Half-metallic behavior Co2YAl (Y= Mo,Tc) compounds

The present manuscript reports structural stability, half-metallic behavior, thermophysical and thermoelectric properties of Co2MoAl and Co2TcAl full Heusler compounds using first-principle calculations. The full-potential linearized augmented plane wave method within the framework of density functional theory is implemented and WIEN2k code is incorporated in the stable Fm- 3m phase to attain the desired results. The L21 phase is found as the most stable phase for both compounds. The optimized equilibrium lattice parameters in the stable phase are 5.89Å, 5.86Å for Co2MoAl and Co2TcAl respectively. The electronic band structure study proves that both compounds Co2MoAl and Co2TcAl have indirect band gaps of 0.74eV and 0.85eV respectively in majority spin alignment. The half-metallic performance of the present set of compounds is explained by the spin-resolved density of states. The Fermi level at the Brillouin zone point approves the metallic as well as semiconducting behavior. To elucidate the thermodynamical stability of these materials against pressure and temperature by implementing the quasi-harmonic approximation of various parameters like Debye temperature, Gruneisen parameters and specific heat are studied successfully. To know the thermoelectric response, Seebeck coefficient and electrical conductivity are computed using the BoltzTrap code. The thermodynamic profile delivers that the present set of compounds possesses no anomalies with respect to the phase transition or instabilities. The computational study insights that the compounds can be synthesized experimentally and find a route towards spintronic and thermoelectric applicability.

First-principles calculations to investigate structural stability, half-metallic behavior, thermophysical and thermoelectric properties of Co2YAl (Y = Mo, Tc) full Heusler compounds

The present manuscript reports structural stability, half-metallic behavior, thermophysical and thermoelectric properties of Co2MoAl and Co2TcAl full Heusler compounds using first-principle calculations. The full-potential linearized augmented plane wave method within the framework of density functional theory is implemented and WIEN2k code is incorporated in the stable Fm-3 m phase to attain the desired results. The L21 phase is found as the most stable phase for both compounds. The optimized equilibrium lattice parameters in the stable phase are 5.89 Å, 5.86 Å for Co2MoAl and Co2TcAl respectively. The electronic band structure study proves that both compounds Co2MoAl and Co2TcAl have indirect band gaps of 0.74 eV and 0.85 eV respectively in majority spin alignment. The half-metallic performance of the present set of compounds is explained by the spin-resolved density of states. The Fermi level at the Brillouin zone point approves the metallic as well as semiconducting behavior. To elucidate the thermodynamical stability of these materials against pressure and temperature by implementing the quasi-harmonic approximation of various parameters like Debye temperature, Gruneisen parameters and specific heat are studied successfully. To know the thermoelectric response, Seebeck coefficient and electrical conductivity are computed using the BoltzTrap code. The thermodynamic profile delivers that the present set of compounds possesses no anomalies with respect to the phase transition or instabilities. The computational study insights that the compounds can be synthesized experimentally and find a route towards spintronic and thermoelectric applicability.

Investigation of Mn doped BaS for spintronic and thermoelectric applications

In this paper, the first principle investigations are performed to compute the electronic, optical, magnetic and thermoelectric (TE) features of Ba1−xMnxS (x = 6.25%, 12.5% and 25%) alloys by using density functional theory (DFT). The semiconductor behavior of pure BaS and half metallic ferromagnetic (HMF) nature of Ba1−xMnxS (x = 6.25%, 12.5% and 25%) is confirmed by investigating electronic band structure (EBS) with spin-resolved density of states (DOS). The MTot is mainly originated from Mn atom due to the presence of 3d-orbitals. In addition, the optical constants including refractive index, absorption and optical spectrum, reflectivity and dielectric function are analyzed in the span of 0–10 eV. It is found that the studied alloy operate within visible to ultraviolet (UV) energy range. Moreover, the TE properties such as figure of merit (ZT), power factor (PF), electrical and thermal conductivity are also calculated by using the BoltzTrap package. The high values of ZTof Ba1−xMnxS (x = 6.25%, 12.5% and 25%) qualify it for use in TE applications.The outcomes revealed the application of Ba1−xMnxS in spintronic and TE gadgets.

DensityTool: A post-processing tool for space- and spin-resolved density of states from VASP

The knowledge of the local electronic structure of heterogeneous solid materials is crucial for understanding their electronic, magnetic, transport, optical, and other properties. VASP, one of the mostly used packages for density-functional calculations, provides local electronic structure either by projecting the electronic wave functions on atomic spheres, or as a band-decomposed partial charge density. Here, we present a simple tool which takes the partial charge density and the energy eigenvalues calculated by VASP as input and constructs local charge and spin densities. The new data provides a much better spatial understanding than the projection on the atomic spheres. It can be visualized directly in the real space e.g. with Vesta, or averaged along planes spanned by two of the lattice vectors of the periodic unit cell. The plane-averaged local (spin) density of states can be easily plotted e.g. as color-coded data using almost any plotting program. DensityTool can be applied to visualize and understand the local electronic structure of any system calculated with VASP. We expect it to be useful especially for researchers concerned with inhomogeneous systems, such as interfaces, defects, surfaces, adsorbed molecules, or hybrid inorganic-organic composites. Program summaryProgram Title: DensityToolCPC Library link to program files:https://doi.org/10.17632/26mcg4jwvd.1Developer's repository link:https://github.com/llodeiro/DensityToolLicensing provisions: MITProgramming language: FORTRANSupplementary material: A complementary User Manual and examples can be found in the developer's repository link.Nature of problem: Total and local density of states (LDOS) are widely-used quantities for understanding the electronic structure of condensed matter. In VASP, one of the mostly used packages for numerically solving the Kohn-Sham equations of density-functional theory, one does not directly obtain the LDOS. Usually, one works with partial density of states (PDOS), where the wave function is projected onto atomic orbitals. Alternatively, it is possible to calculate the band- and wavevector-dependent charge densities. Together with the band structure, LDOS can be obtained using post-processing tools.Solution method: DensityTool combines the band structure with band- and wavevector-dependent charge densities calculated by VASP to construct LDOS. In addition, spin-resolved LDOS (LSDOS) can be calculated for magnetic systems. Thus obtained LDOS and LSDOS can be further processed with DensityTool. In particular, it can be averaged along chosen spatial directions, which is convenient for example to demonstrate the spatially-resolved electronic structure of inhomogeneous systems.DensityTool can handle all three types of approaches implemented in VASP (non-magnetic, collinear magnetic, non-collinear magnetic including spin-orbit coupling), as well as all types of self-consistent band calculations as DFT (e.g., LDA, GGA, mGGA, BJ, and hybrid exchange-correlation functionals) and HF.For convenience, the output of DensityTool follows the format of VASP (the CHGCAR file), which can be easily used in other programs for visualization. We provide a sample python script to plot averaged L(S)DOS from the calculated data.

Half-metallicity in smallest cage-like cluster of CdTe with doping of transition metal atoms

We report first principles theory based electronic structure studies of a semiconducting stoichiometric cage-like Cd9Te9 cluster. Substantial changes are observed in the electronic structure of the cluster on passivation with fictitious hydrogen atoms, in particular, widening of the energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital and enhancement in stability of cluster is seen. The cluster, when substitutionally mono-doped for a Cd by a set of 3d and 4d transition metal atoms (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh and Pd), is found to acquire polarization as seen from spin resolved density of states near Fermi level. Further, such mono-doping in passivated cluster shows half-metallic behavior. Mapping of partial density of states of each system on that of undoped cluster reveals additional levels caused by doping each TM atom separately. In the 3d elemental doping, Ti and Mn doping result into electron type doping whereas all other cases result into hole doped systems. For all the 4d elements studied, it is akin to the doping with holes for Cd substitution in the outer ring, whereas for Ru and Rh, there is electron type doping in case of substitution for Cd in central ring upon passivation. A comparison of partial density of states plots for bare and passivated clusters, on doping with transition metal atoms, suggests suitability of the cage-like cluster for spintronics applications.

Temperature dependent transition of conduction mechanism from carrier injection to multistep tunneling in Fe3O4 (111)/Alq3/Co organic spin valve

We have presented experimental results addressing the origin of spin valve (SV) magneto-resistance (MR), in both injection and tunnel conduction regimes, in our fabricated Fe 3 O 4 (111)/Alq 3 /Co SV device. Experimental evidences have shown that any alternative MR process, such as ‘tunneling anisotropic MR’ is not at the origin of this SV MR. Spin resolved density of states of electrodes indicate that both the conduction mechanisms induce different spin dependent scattering which inturn modify the MR signal of the device. This modification helped in maintaining a non-monotonous quenching of MR signal with increase in temperature. We have also proposed a phenomenological model for device operation where the concept of charge gap modification at Fermi level across Verwey transition is envisaged to offer this unique scenario of tuning the conduction mode and hence MR in this ferrite based organic SV. The model is also supported by an established theoretical study which considers high temperature phonon assisted tunneling through defect states at electrode–organic interface of the device. • Conduction mechanism transition from carrier injection to multistep tunneling. • Transition due to Verwey transition of Fe 3 O 4 . • Spin flip scattering at Alq 3 spacer above Verwey transition temperature. • Non-monotonous MR quenching with temperature. • Room temperature MR signal of hybrid spin valve.

Minigap Suppression in S(N/F)S Junctions

We consider a long diffusive Josephson junction where the weak link is a thin (normal metal (N)–ferromagnet (F)) bilayer (N and F form parallel links between superconductors (Ss)). We show that superconductivity in the weak link can be described by an effective one-dimensional Usadel equation containing a “diluted” exchange field as well as a weak depairing term that is caused by the inherent inhomogeneity of the bilayer. The depairing mechanism distinguishes the S(N/F)S system from an SFS junction and affects the density of states of the S(N/F)S junction. It results in the suppression of the minigap in the spin-resolved density of states. The depairing rate and the minigap are expressed in terms of geometrical parameters, the Thouless energy and the effective exchange field. The effective one-dimensional theory can be applied to various structures with thin inhomogeneous links and shows good agreement with numerical solutions of the original two-dimensional equations. We also discuss ways to reveal the predicted effect experimentally.

Low Magnetic Damping of Epitaxial NiFe (100) Thin Films Grown on Different Substrate

The magnetic properties and Gilbert damping constant α of NiFe films grown on different substrates at different sputtering temperatures were investigated. NiFe films with low Gilbert damping constant α of 0.0046 (TiN) and 0.0055 (MgO) at 500°C were obtained. It is found that the crystal structure and lattice mismatch strongly affected the Gilbert damping constant α. With increasing the sputtering temperature, the NiFe gradually changed from amorphous to crystalline, thus the chemical ordering increased, which would cause the decrease of the density of states at Fermi level (D(EF)) and the Gilbert damping constant α. Moreover, the damping constant exhibited a slight decrease with increasing the mismatch strain, which would be further proven by the spin resolved density of states for the NiFe films. This study may offer a fabrication method of the NiFe films with small damping constant α in the applications of the STT-MRAM device’s area.

Non-conventional ferromagnetism and high bias magnetoresistance in [formula omitted]: A simple phenomenological approach

A simple phenomenological approach is used to describe magnetization and magnetoresistance in thin films of oxygen-deficient rutile titanium dioxide (TiO2). Magnetization curves were successfully simulated by considering the ferromagnetic (FM) contribution of magnetically interacting oxygen vacancies (VO’s) forming a single-domain using the Stoner-Wohlfarth (SW) model combined with paramagnetic (PM) contribution of isolated VO’s described by a Langevin function. Whereas approximately half of the VO’s behave as ferromagnetically coupled, rotating coherently with the applied magnetic field, the remaining half of the VO’s tend to align individually with the local magnetic field overcoming the thermal fluctuation deviations. The conduction mechanism is described by variable range hopping (VRH) regime with electron hopping between VO’s centers in the TiO2-x matrix. The magnetoresistance (MR) curves are consistently simulated through the scaling with square of PM contribution of magnetization, indicating that resistance depends on the relative orientation of the magnetic moments associated with non-interacting VO’s dispersed in TiO2 matrix at low temperatures. Density functional theory (DFT) calculations were performed to validate the parametrization of the phenomenological approach used to described the ferromagnetic groundstate of the VO network and spin polarization in the VRH regime in the TiO2-x matrix. Spin-resolved density of states (DOS) calculations consistently reveal that magnetoresistance can be ascribed to electron hopping from defect-states located immediately below Fermi level to the bottom of conduction band states with an opposed spin-polarization.

Charge transfer and hybridization effect at the graphene-nickel interface: A tight binding model study

We have investigated here, the electronic and magnetic properties of graphene–nickel system by tight-binding mean-field approach. Strong hybridization between the 2pz orbital of graphene and 3dz2 orbital of nickel occurs when monolayer graphene is placed over a single layer of ferromagnetically ordered Ni (111) metal due to the excellent lattice matching between the two layers. This hybridization greatly affects the electronic and magnetic properties of the bilayer system, resulting in a significantly reduced local magnetic moment of the nickel layer and an enhanced induced spin polarization on the graphene layer. The calculated Hamiltonian revealed critical information regarding the first-, second-and third-nearest-neighbour hopping integrals of π− electrons of graphene besides the Coulomb correlation of electrons in nickel (111). The Hubbard type Coulomb interactions present in nickel lattices were treated within the mean-field approximation. Zubarev's technique was employed to calculate electronic Green's functions and subsequent investigation of the temperature dependent ferromagnetic magnetization of nickel (111)was carried out through self-consistent calculation. Further calculations regarding the induced magnetization in the graphene, total magnetization in bilayer layer system, electronic band dispersion, spin resolved density of states (DOS) and spin polarization efficiency have been carried out. The results were corroborated by experimental observations.

Nonequilibrium Kondo effect in a magnetic field: auxiliary master equation approach

We study the single-impurity Anderson model out of equilibrium under the influence of a bias voltage ϕ and a magnetic field B. We investigate the interplay between the shift () of the Kondo peak in the spin-resolved density of states (DOS) and the one () of the conductance anomaly. In agreement with experiments and previous theoretical calculations we find that, while the latter displays a rather linear behavior with an almost constant slope as a function of B down to the Kondo scale, the DOS shift first features a slower increase reaching the same behavior as only for . Our auxiliary master equation approach yields highly accurate nonequilibrium results for the DOS and for the conductance all the way from within the Kondo up to the charge fluctuation regime, showing excellent agreement with a recently introduced scheme based on a combination of numerical renormalization group with time-dependent density matrix renormalization group.

First-principal study of full Heusler alloys Co2VZ (Z = As, In)

We have used full-potential linearized augmented plane wave method in the stable Fm-3m phase to investigate the structural, elastic, magnetic and electronic properties of Co2VZ (Z=As, In). The optimized equilibrium lattice parameter in stable phase is 5.80Å for Co2VAs and 6.01Å for Co2VIn. Ferromagnetic behavior of both the alloys is explained by the spin resolved density of states. The exchange splitting due to Co and V atoms are responsible for the ferromagnetic behaviour. No energy gap is found in spin up state while an energy gap can be seen in spin down state, hence, showing half-metallic nature. Elastic stability is discussed through elastic constants. Thermodynamic properties of the alloys have been obtained by using the quasi-harmonic approximations. Boltzmann theory is employed to investigate the electronic transport properties of these alloys.

Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations

Density functional theory calculations were carried out for three entropic rocksalt oxides, (Mg0.1Co0.1Ni0.1Cu0.1Zn0.1)O0.5, termed J14, and J14 + Li and J14 + Sc, to understand the role of charge neutrality and electronic states on their properties, and to probe whether simple expressions may exist that predict stability. The calculations predict that the average lattice constants of the ternary structures provide good approximations to that of the random structures. For J14, Bader charges are transferable between the binary, ternary, and random structures. For J14 + Sc and J14 + Li, average Bader charges in the entropic structures can be estimated from the ternary compositions. Addition of Sc to J14 reduces the majority of Cu, which show large displacements from ideal lattice sites, along with reduction of a few Co and Ni cations. Addition of Li to J14 reduces the lattice constant, consistent with experiment, and oxidizes some of Co as well as some of Ni and Cu. The Bader charges and spin-resolved density of states (DOS) for Co+3 in J14 + Li are very different from Co+2, while for Cu and Ni the Bader charges form continuous distributions and the two DOS are similar for the two oxidation states. Experimental detection of different oxidation states may therefore be challenging for Cu and Ni compared to Co. Based on these results, empirical stability parameters for these entropic oxides may be more complicated than those for non-oxide entropic solids.

Magnetic phase transition of Ag2S:Eu diluted magnetic semiconductor nanoparticles

In this study, we synthesize europium doped Ag2S diluted magnetic semiconductor (DMS) nanoparticles using a gas–liquid phase chemical deposition process. It has been found that the Ag2S:Eu nanoparticles have room-temperature ferromagnetism (RTF) and display two remarkable magnetic phase transitions with decreasing temperature, i.e., the classic thermally driven transition from superparamagnetism to blocked superparamagnetism and the quantum phase transition from magnetic long-range order to quantum superparamagnetism state. When the blocking temperature (TB, 300 K) is reached, the first magnetic phase transition from superparamagnetism to blocked superparamagnetism is observed; after further temperature decrease to the critical phase transition temperature (TC, 11 K) the second magnetic phase transition which is from magnetic long-range order to quantum superparamagnetism is observed because of the quantum tunnelling effect. The spin-resolved density of states is calculated by the software VASP (Vienna Ab-initio Simulation Package) to investigate the origin of magnetism of the Ag2S:Eu nanoparticles. It is found that the magnetism originates from the doped Eu atoms and is caused by an f–f exchange interaction of Eu ions.

Electronic and magnetic properties of bulk Cr tips for scanning tunneling spectroscopy

The electronic and magnetic properties of bulk Cr tips for scanning tunneling microscopy have been investigated by means of density functional theory (DFT) calculations and scanning tunneling spectroscopy (STS) measurements. Spin-resolved densities of states (DOS) were calculated for model tips, i.e., Cr adatoms and clusters on ideal Cr surfaces. STS measurements on Au(111) and Si(111)-7x7 have been interpreted by modeling the tunneling process in a Wentzel-Kramers-Brillouin approximation in order to ascertain the role of tip DOS features. Calculated spin-resolved electronic properties of Cr tips have been used to revisit spin-polarized (SP) STS measurements from the literature. The agreement between experimental findings and DFT calculations confirms the relevance of the knowledge of tip electronic properties and of an appropriate model for the tunneling process in the interpretation of STS and SP-STS data.